Poly (lactic acid) blends: Processing, properties and applications

International Journal of Biological Macromolecules 125 (2019) 307–360

Contents lists available at ScienceDirect

International Journal of Biological Macromolecules journal homepage: http://www.elsevier.com/locate/ijbiomac

Review

Poly (lactic acid) blends: Processing, properties and applications Mohammadreza Nofar a,b,⁎, Dilara Sacligil b, Pierre J. Carreau c, Musa R. Kamal d, Marie-Claude Heuzey c a

Metallurgical & Materials Engineering Department, Faculty of Chemical and Metallurgical Engineering, Istanbul Technical University, Maslak, Istanbul 34469, Turkey Polymer Science and Technology Program, Istanbul Technical University, Maslak, Istanbul 34469, Turkey c Center for High Performance Polymer and Composite Systems (CREPEC), Chemical Engineering Department, Polytechnique Montreal, Montreal, Quebec H3T 1J4, Canada d CREPEC, Chemical Engineering Department, McGill University, Montreal, Quebec H3A 2B2, Canada b

a r t i c l e

i n f o

Article history: Received 21 September 2018 Received in revised form 29 November 2018 Accepted 1 December 2018 Available online 07 December 2018 Keywords: Poly(lactic acid) Polylactide PLA Stereocomplex Multiphase Blend Binary Ternary Composite Nanocomposite Foam Review

a b s t r a c t Poly (lactic acid) or polylactide (PLA) is a commercial biobased, biodegradable, biocompatible, compostable and non-toxic polymer that has competitive material and processing costs and desirable mechanical properties. Thereby, it can be considered favorably for biomedical applications and as the most promising substitute for petroleum-based polymers in a wide range of commodity and engineering applications. However, PLA has some significant shortcomings such as low melt strength, slow crystallization rate, poor processability, high brittleness, low toughness, and low service temperature, which limit its applications. To overcome these limitations, blending PLA with other polymers is an inexpensive approach that could also tailor the final properties of PLAbased products. During the last two decades, researchers investigated the synthesis, processing, properties, and development of various PLA-based blend systems including miscible blends of poly L-lactide (PLLA) and poly Dlactide (PDLA), which generate stereocomplex crystals, binary immiscible/miscible blends of PLA with other thermoplastics, multifunctional ternary blends using a third polymer or fillers such as nanoparticles, as well as PLA-based blend foam systems. This article reviews all these investigations and compares the syntheses/ processing-morphology-properties interrelationships in PLA-based blends developed so far for various applications. © 2018 Elsevier B.V. All rights reserved.

Contents 1. 2.

3.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . Miscible PLA/PLA blends-effect of stereocomplex crystals . . . . 2.1. Crystallization behavior. . . . . . . . . . . . . . . . 2.2. Mechanical properties . . . . . . . . . . . . . . . . 2.3. Rheological properties . . . . . . . . . . . . . . . . 2.4. Degradation and permeability . . . . . . . . . . . . . PLA binary blends with other biopolymers (bioblends) . . . . . 3.1. Blends of PLA with biobased and biodegradable polymers 3.1.1. PLA-Starch . . . . . . . . . . . . . . . . . 3.1.2. PLA-lignin. . . . . . . . . . . . . . . . . . 3.1.3. PLA-PHAs . . . . . . . . . . . . . . . . . . 3.2. Blends of PLA with biodegradable polymers . . . . . . 3.2.1. PLA-PCL. . . . . . . . . . . . . . . . . . . 3.2.2. PLA-PBAT . . . . . . . . . . . . . . . . . . 3.2.3. PLA-PBSA . . . . . . . . . . . . . . . . . . 3.2.4. PLA-PBS . . . . . . . . . . . . . . . . . . 3.2.5. PLA-PVAc . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

309 312 313 315 315 315 315 315 315 317 317 318 318 319 320 320 320

⁎ Corresponding author at: Metallurgical & Materials Engineering Department, Faculty of Chemical and Metallurgical Engineering, Istanbul Technical University, Maslak, Istanbul 34469, Turkey. E-mail address: [email protected] (M. Nofar).

https://doi.org/10.1016/j.ijbiomac.2018.12.002 0141-8130/© 2018 Elsevier B.V. All rights reserved.

308

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

3.2.6. PLA-PVA or PVOH . . . . . . . . . . . . . . 3.2.7. PLA-EVOH . . . . . . . . . . . . . . . . . . 3.2.8. PLA-PPC . . . . . . . . . . . . . . . . . . . 3.2.9. PLA-PES . . . . . . . . . . . . . . . . . . . 3.2.10. PLA-PGA . . . . . . . . . . . . . . . . . . 3.3. Blends of PLA with biobased polymers . . . . . . . . . 4. PLA binary blends with synthetic/nondegradable thermoplastics . 4.1. PLA-PE . . . . . . . . . . . . . . . . . . . . . . . 4.2. PLA-PP . . . . . . . . . . . . . . . . . . . . . . . 4.3. PLA-PS . . . . . . . . . . . . . . . . . . . . . . . 4.4. PLA-ABS . . . . . . . . . . . . . . . . . . . . . . . 4.5. PLA-PMMA . . . . . . . . . . . . . . . . . . . . . 4.6. PLA-PET . . . . . . . . . . . . . . . . . . . . . . . 4.7. PLA-PBT . . . . . . . . . . . . . . . . . . . . . . . 4.8. PLA-PTT . . . . . . . . . . . . . . . . . . . . . . . 4.9. PLA-PC . . . . . . . . . . . . . . . . . . . . . . . 4.10. PLA-PA . . . . . . . . . . . . . . . . . . . . . . . 4.11. PLA-PEG, PEO, or POE . . . . . . . . . . . . . . . . 4.12. PLA-POM . . . . . . . . . . . . . . . . . . . . . . 4.13. PLA-PVPh. . . . . . . . . . . . . . . . . . . . . . 5. PLA binary blends with elastomeric polymers . . . . . . . . . 5.1. PLA-rubber . . . . . . . . . . . . . . . . . . . . . 5.1.1. PLA-NR (natural rubber) . . . . . . . . . . . 5.1.2. PLA-SBS . . . . . . . . . . . . . . . . . . . 5.1.3. PLA-SEBS . . . . . . . . . . . . . . . . . . 5.1.4. PLA-other rubber elastomers . . . . . . . . . 5.2. PLA-PU . . . . . . . . . . . . . . . . . . . . . . . 5.2.1. PLA-thermoset PU . . . . . . . . . . . . . . 5.2.2. PLA-thermoplastic PU. . . . . . . . . . . . . 5.3. PLA-EVA and EVM . . . . . . . . . . . . . . . . . . 6. PLA binary blends with other polymers . . . . . . . . . . . . 7. PLA ternary or hybrid blends . . . . . . . . . . . . . . . . . 7.1. Blends of ternary polymers . . . . . . . . . . . . . . 7.2. PLA blend nanocomposites . . . . . . . . . . . . . . 7.2.1. PLA blends with nanoclay . . . . . . . . . . . 7.2.2. PLA blends with carbon nanotubes . . . . . . . 7.2.3. PLA blends with cellulose nanocrystals . . . . . 7.2.4. PLA blends with graphene-based nanoparticles . 7.2.5. PLA blends with nanosilica . . . . . . . . . . 7.2.6. PLA blends with other nanoparticles . . . . . . 7.2.7. PLA blends with chitosan . . . . . . . . . . . 8. PLA blend foams . . . . . . . . . . . . . . . . . . . . . . 8.1. Miscible PLA-PLA blend foams . . . . . . . . . . . . . 8.2. PLA bioblend foams . . . . . . . . . . . . . . . . . . 8.3. PLA blend foams with synthetic/nondegradable polymers 8.4. PLA blend foams with elastomeric polymers. . . . . . . 9. Conclusion, challenges and future perspectives . . . . . . . . . References. . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Introduction Petroleum-based polymers are widely used in the production of various polymeric products for different commodity, engineering, and advanced applications. However, the depletion of oil resources as well as the volatility of oil prices are of global concern in relation to the production of synthetic polymers. Moreover, the use of petroleum-based polymers has been a serious concern of the environmentalists as the majority of these polymers persist as non-degradable waste materials in the environment. Therefore, to remediate these issues efforts have been directed to the production of biodegradable polymers from renewable agricultural resources [1]. Poly (lactic acid) or polylactide (PLA), an aliphatic thermoplastic polyester, is one of the most extensively developed commercial biobased, biodegradable, and biocompatible polymers. It is derived from resources such as cornstarch, sugarcane, and other renewable biomass products and wastes. As shown in Fig. 1, PLA can be synthesized

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

321 321 321 321 321 321 322 322 323 323 323 324 324 324 324 325 325 325 326 326 326 326 326 328 328 328 329 329 329 330 331 332 333 335 335 337 338 338 339 339 339 340 340 341 344 344 345 346

through either direct condensation polymerization of lactic acid monomer or ring-opening polymerization of cyclic lactide dimer. In general, the ring-opening approach is used commercially to produce solventfree high molecular weight PLA, since in the other approach water is also produced as an undesirable coproduct during polymerization [2–4]. In addition to its competitive material and processing costs, PLA exhibits attractive mechanical and physical properties (e.g., high modulus, high strength, good clarity and barrier properties). These properties make PLA a suitable candidate, in commodity and engineering applications, to replace some important petroleum-based polymers such as polystyrene (PS), polyethylene terephthalate (PET), high-density polyethylene (HDPE), and polypropylene (PP). Some of these applications include film and packaging, textile and fiber, construction and automotive products [1,2,4–8]. Moreover, due to its biocompatibility, non-toxic features, and biodegradability, PLA is commonly considered for biomedical applications such as drug delivery, blood vessels, tissue engineering and scaffolding [9–11].

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

T1:1

Nomenclature

T1:2 T1:3 T1:4 T1:5 T1:6 T1:7 T1:8 T1:9 T1:10 T1:11 T1:12 T1:13 T1:14 T1:15 T1:16 T1:17 T1:18 T1:19 T1:20 T1:21 T1:22 T1:23 T1:24 T1:25 T1:26 T1:27 T1:28 T1:29 T1:30 T1:31 T1:32 T1:33 T1:34 T1:35 T1:36 T1:37 T1:38 T1:39 T1:40 T1:41 T1:42 T1:43 T1:44 T1:45 T1:46 T1:47 T1:48 T1:49 T1:50 T1:51 T1:52 T1:53 T1:54 T1:55 T1:56 T1:57 T1:58 T1:59 T1:60 T1:61 T1:62 T1:63

ABS acrylonitrile-butadiene-styrene APMS aminopropyl trimethoxy silane APP ammonium polyphosphate APTES aminopropyl triethoxysilane ATBC acetyl tributyl citrate ATC acetyl triethyl citrate BAI Boehmit CE chain extender CNC cellulose nanocrystals CNT carbon nanotubes CPMS chloropropyl trimethoxysilane DCP dicumyl peroxide DFA dimer fatty acid DFAPA dimer fatty acid polyamide DIH diisocyanatohexane DMA dynamic mechanical analysis DOM dioctyl maleate DSC differential scanning calorimetryf EBA-GMA ethylene-butyl acrylate-glycidyl methacrylate EGMA ethylene-co-glycidyl methacrylate E-GMA ethylene-glycidyl methacrylate EGVA ethylene-glycidyl methacrylate-vinyl acetate EMAA-Zn zinc ionomer of ethylene-methyacrylic acid copolymer EMA-GMA ethylene-methyl acrylate-glycidyl methacrylate ENR epoxidized natural rubber EOR poly(ethylene-co-octene) EPO epoxidized palm oil EPR ethylene propylene rubbe ESBS epoxidized-poly(styrene-butadiene-styrene) ESO epoxidized soybean EVA ethylene-vinyl acetate EVM ethylene-vinyl acetate rubber EVOH ethylene vinyl alcohol FTIR Fourier transfer infrared g-A grafted amylose g-AC grafted acrylic acid g-GMA grafted glycidyl methacrylate GMA glycidyl methacrylate g-MA grafted maleic anhydride GPMS glycidoxypropyl trimethoxysilane HBP hyper-branched poly(ester-amide) HDI hexamethylene diisocyanate HDPE high-density polyethylene HDT heat deflection temperature HNT halloysite nanotube IPD isoporone diisocyanate ITPB isocyanate-terminated prepolymer of polybutadiene LAOS large amplitude oscillatory shear LDI lysine diisocyanate LDPE low density polyethylene LLDPE linear low density polyethylene LNR liquid natural rubber LOI limiting oxygen index LPB liquid polybutadiene rubber LTI lysine triisocyanate MA maleic anhydride MDI methylene diphenyl diisocyanate MFI melt flow index MMA methyl methacrylate MMT montmorillonite Mw molecular weight MWCNTs multiwalled carbon nanotubes

NBR NR OMMT PA PAE PAni PB PBA PBAT PBS PBSA PBSL PBT PC PCL PDI PDLA PDLLA PDMS PE PEBA PEG PEO PEOc PEPG PES PET PEVA PGA PGMA PHAs PHB PHBHHx PHBV PHEE PHV PIF PLA PLLA PMMA POE POM POSS PP PPC PPD PPDI PPO PS PTT PU PVAc PVB PVDF PVOH PVP PVPh SAN SAXS SBS SC SEBS SEBS SiO2

309

acrylonitrile–butadiene rubber natural rubber organo-modified montmorillonite polyamide polyamide elastomer polyaniline polybutadiene poly(butyl acrylate) poly(butylene adipate-co-terephthalate) poly(butylene succinate) poly(butylene succinate-co-adipate) poly(butylene succinate-co-l-lactate) poly(butylene terephthalate) polycarbonate polycaprolactone phenylene diisocyanate poly (D-lactic acid) or poly D-lactide poly (D, L-lactic acid) poly(dimethyl siloxane) polyethylene polyether-b-amide poly (ethylene glycol) polyethylene oxide poly(ethylene-co-octene) poly(ethylene glycol-co-propylene glycol) poly(ethylene succinate) polyethylene terephthalate poly(ethylene-co-vinyl acetate) poly(glycolic acid) polyolefin grafted maleic anhydride polyhydroxyalkanoates poly(3-hydroxybutyrate) poly(3-hydroxybutyrate butyrate-co-3-hydroxyhexanoate) polyhydroxybutyrate-co-valerate polyhydroxy ester ether polyhydroxyvalerate pressure-induced flow poly (lactic acid) or polylactide poly (L-lactic acid) or poly L-lactide poly(methyl methacrylate) polyoxyethylene poly(oxymethylene) polyhedral oligomeric silsesquioxane polypropylene poly(propylene carbonate) poly-p-dioxanone paraphenylene diisocyanate polypropylene oxide polystyrene poly(trimethylene terephthalate) polyurethane polyvinyl acetate poly(viny1 butyral) polyvinylidene fluoride poly(vinyl alcohol) Poly(vinylpyrrolidone) poly(vinylphenol) styrene-acrylonitrile small angle X-ray diffraction poly(styrene-butadiene-styrene) stereocomplex poly(styrene-ethylene-butylene-styrene) styrene-ethylene-butylene-styrene silica

310

TC TDI Tg TGA Tm TNBT TOA TOC TPO TPP TPS TPU VA WAXD Xc γpx γx γdx γxy ΔH λ

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

triethyl citrate toluene diisocyanate glass transition temperature thermal gravimetric analysis melting temperature tetrabutyl titanate tung oil anhydride tocopherol thermoplastic polyolefin elastomer triphenyl phosphite thermoplastic starch thermoplastic polyurethane vinyl acetate wide angle X-ray diffraction degree of crystallinity polar contribution to the surface tension of material x surface tension of material x dispersive contribution to the surface tension of material x interfacial tension between components x and y heat enthalpy spreading coefficient

Besides the above noted advantages, PLA also suffers from serious drawbacks, which restrict its production and usage in different applications. These limitations are mainly due to PLA's inherently low melt strength and slow crystallization rate, which hamper its processability, formability, and foamability [6,7,12–14]. Moreover, despite its superior modulus and strength, PLA is brittle and has very low toughness. As a result of its low glass transition temperature (Tg), which is in the range 55–60 °C, and slow crystallization rate, PLA possesses low service temperature (i.e. low heat deflection temperature, or HDT), which limits its usage at relatively low service temperatures [13–16]. One of the methods, although expensive, that has been initiated since more than two decades ago is to develop copolymers of PLA with other tough, ductile, and/or elastomeric monomers [3,14,17]. In very early studies, copolymers of L-lactide and ε-caprolactone as biodegradable elastomeric implant materials were developed with high toughness and ductility [18]. Supertough PLA products were also introduced by developing poly(lactide-co-glycolide) copolymers modified with ε-caprolactone [19]. Furthermore, ductility and toughness were

Fig. 1. Synthesis of PLA through direct condensation and ring-opening polymerizations [4].

highly improved when trimethylene carbonate and caprolactone were copolymerized with lactide and then blended with PLA [20]. Due to the biocompatibility and hydrophilicity of ethylene glycol, it is considered as another common copolymer with PLA [14]. Very recently Fan et al. [21–22] revealed how the use of flexible copolymers of PLA could effectively be incorporated in drug delivery and oxygen carriers in biomedical treatments. Although in some biomedical applications the quality of the final product is the most critical criteria, in most commodity and engineering applications and even sometimes in biomedical applications, the cost of the final products plays an important role. In this context, a practically very common and more cost-effective approach to overcome the above mentioned limitations of PLA is to blend PLA with other polymers. Thus, the blend should exhibit a superior behavior in areas where PLA shows weaknesses, in order to compensate for them [23–24]. Moreover, development of PLA blend systems also opens new avenues to extend PLA applications in commodity and engineering areas such as plastic utensils, packaging (i.e., filma and bottle manufacturing), cushioning, thermal and sounds insulation, construction and automotive as well as in biomedical applications such as tissue engineering, scaffolding, drug deleivery, blood vessels, and biosensors [9,25]. This will be possible through controlling/tailoring the ratio of PLA to the secondary blending polymer, the use of a third blending polymer or introducing functional nanoparticles, and controlling the morphology and localization of blending components, as well as benefiting from the generated synergies of interfacial interactions among the blending elements [23–24,26–27]. According to equilibrium thermodynamics, two polymers would be miscible when the Gibb's free energy of a mixing is negative, and the outcome would be a uniform single phase product with averaged properties. In this rarely occurring case, both polymers are to be fully miscible, obviously compatible, and the interfacial tension between them should be close to zero. On the other hand, most polymers are practically immiscible and the existence of an interphase and interfacial interactions between the polymeric components plays a major role on the blend structure-properties. Due to the existence of independent phases, the transition temperatures of each component would also appear separately [28]. Hence, if the two polymers are not compatible, their interfacial tension would be, relatively, very high; each polymer would show its own Tg and the final properties of the blend could be weak. However, when the two immiscible polymers are more compatible, the interfacial tension will be, relatively, reduced and thereby the interfacial adhesion between the two phases is enhanced. In such cases, the Tg values are closer to each other and the blend final properties could synergistically be greater than those of the constituent materials [23–24,28–29]. The improvement of the final properties is not only determined by the intrinsic properties of the blend components, but it also significantly depends on the morphology of the blend. Typical morphologies include droplet-type and double emulsion, laminar, fibrillar, co-continuous or ordered structures. The corresponding resulting properties of morphological changes could be: improved toughness, enhanced barrier properties, enhanced strength and thermal expansion, and increased electrical conductivity through the use of conductive additives [23–24]. The achievement of these morphologies is dependent on the ratio of the blended polymers and their respective viscoelastic properties, as well as on the selected processing method [29–32]. For each morphology, the distribution and homogeneity of the polymeric components are dependent on their viscosity ratio, interfacial tension [24,29,33], the use of compatibilizers, addition of a third phase [26–27,34–35], process type and processing parameters [24,29,31–32]. For instance, in applications where droplet-like morphology is favorable, a finer dispersed phase may be obtained when the viscosity ratio of the blend components is closer to one [30]. Also, applying severe shear forces during melt mixing can produce finer droplets, although long residence time and/or re-processing of a blend with droplet-like morphology could result in coarsening and drop coalescence

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

[23,36,37]. The surface energy of each polymer component and hence the interfacial tension is also of great importance in determining the final blend morphology and its stability [38]. In blends with dropletlike morphologies, lower interfacial tension between the two components would lead to a reduction of droplet size of the dispersed phase [24]. In this context, the use of compatibilizer could decrease the interfacial tension and hence finer droplets may be obtained. The geometricmean equation [38] is a useful relationship to estimate the interfacial tension between two components of a blend system:  12  12  γ xy ¼ γx þ γy −2 γ dx γdy þ γ px γpy

ð1Þ

where γxy is the interfacial tension between components x and y, γx is the surface tension of material x and γdx and γpx are the dispersive and polar contributions, respectively, to the surface tension of material x. In a ternary system where the third component is a filler such as nanoparticles, the overall properties of the blend nanocomposite could be affected and other functional properties could be introduced due to the presence of the nanoparticles. In ternary blend nanocomposites, not only the final morphology of the blend but also the interfacial properties between the three components determine the final features of the product [27,35,39]. As a result of the interfacial interactions, the localization of the nanoparticles could occur either in polymer A, polymer B, or at the interface of both polymers. Thus, the final properties are influenced by the localization of the nanoparticles, theoretically determined by the value of the wetting coefficient defined by [40]: ωa ¼ ½ðγ nano−B −γ nano−A Þ=γ A−B 

ð2Þ

where γnano-A and γnano-B are the values of the interfacial tension between nanoparticles and polymers A and B, respectively, and γA-B is the interfacial tension between polymers A and B. If the wetting coefficient is higher than 1 (ωa N 1), nanoparticles will be located in polymer A, while nanoparticles will be located in polymer B if the wetting coefficient is lower than −1 (ωa b −1). For −1 b ωa b 1, nanoparticles will preferentially be located at the interface between the two polymer phases [35,40–41]. In ternary blend systems where the third component is another polymer component, the overall properties of the blends could further be improved by tuning the morphology and intra-component interactions, and thereby some other functional properties could additionally be introduced. The following different morphologies may be obtained in ternary blend systems. In an A-B-C system, complete wetting occurs when phases A and B and phases B and C completely wet each other. In the case of partial wetting, the most stable thermodynamic state is when there is three-phase contact. For instance, droplets of B will locate at the A–C interface such that all three phases are in contact with each other. Both complete and partial wetting can be described by the spreading coefficient as defined by the Harkins equation [42–43]: λAB ¼ γBC −γAC −γ AB

In other words, droplets of one of the polymers locate at the interface and create a three-phase contact [42–44]. Practically, however, morphologies like complete-partial wetting could also be formed where polymer B would not only be encapsulated in polymer C, but would also be located at the interface of polymers A and C [45]. This morphology is considered as a transient morphology from partial wetting towards complete wetting. Thereby, the change in the sign of spreading coefficients could result in the change of morphology and hence, this morphology transition occurs when the spreading coefficient becomes zero. Fig. 2 shows the schematic of possible morphologies of ternary polymer blends containing one major phase (polymer A) and two minor phases (polymers B and C) [45–47]. More complex blend systems with more than three components might also be of interest to scientists to further tailor the final properties of a product, although the characterization of these systems would become quite complicated and tedious. The achievement of lightweight cost-effective products is one of the main objectives in the manufacturing of cellular products. Foaming technologies to manufacture cellular structures from blend systems have become of great interest industrially due to the improvements that could be obtained by foaming, specifically microcellular foaming. In this context, different blend morphologies as well as the solubility/ diffusivity degree of the physical blowing agent in each polymer would play important roles in obtaining cellular blend structures with desired properties [6]. This report reviews the investigations related to PLA-based blends and compares the composition/processing-morphology-properties relationships developed so far for various applications. This includes the overview of the investigations that have been conducted on (i) miscible blends of poly L-lactide (PLLA) and poly D-lactide (PDLA), which generate stereo-complex crystals; (ii) binary immiscible/miscible blends of PLA with other thermoplastics; (iii) multifunctional ternary PLA blends using a third polymer or hybrid systems with fillers such as nanoparticles; and (iv) PLA-based blend foam systems. Fig. 3 provides detailed

ð3Þ

where γ represents the interfacial tensions for the different polymer pairs and indices refer to components of the mixture; λ is defined as the spreading coefficient describing the tendency of component A to encapsulate or spread around component B in a matrix of component C. In blends of one major component (polymer A) and two minor dispersed phases (polymers B and C), several morphologies could be obtained. Each morphology has a distinct set of spreading coefficients. A positive value for λAB determines that polymer A can completely spread over polymer B. In other words, polymer A separates polymers B and C. This generates complete wetting morphology where two-phases are in contact. Three negative spreading coefficients indicate a partial wetting behavior in which none of the three spreads at the interface of other phases and all three meet along a common line of three-phase contact.

311

Fig. 2. Schematic of possible morphologies of ternary polymer blends [45–47].

312

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

Fig. 3. Number of studies reported on various PLA-based blend systems over the last two decades.

information regarding the number of research reports on various PLAbased blend systems over the last two decades, including binary PLA blends with biobased polymers, biodegradable polymers, biobasedbiodegradable polymers, and synthetic-nondegradable polymers (non-biopolymers), ternary polymer blends of PLA with two other polymers, ternary blend nanocomposites of PLA with a polymer and a nanofiller, and PLA-based blend foams. It is clear that research on PLAbased blend systems grown dramatically in different areas during these decades. Fig. 4 also shows the distribution and total number of PLA-based blend publications relating to the various blend systems noted above, as well as the incorporated type of nanofiller in PLAbased ternary blend nanocomposites. 2. Miscible PLA/PLA blends-effect of stereocomplex crystals Lactic acid and lactide molecules can exhibit different stereochemistry configurations. As Fig. 5 shows, lactic acid monomers exist in two forms, i.e. L-lactic acid or D-lactic acid. Moreover, cyclic lactide dimers can exist in three forms: DD-lactide, LL-lactide, or DL-lactide, (also called as meso-lactide). When the backbone of the produced PLA molecules is only L- or D-lactic acid, poly (L-lactic acid) (PLLA) or poly (D-lactic acid) (PDLA) are obtained as homopolymers of PLA, respectively. Besides the production by condensation polymerization of L-lactic acid monomers, PLLA can also be produced by ring-opening polymerization of LL-lactide dimers, which is currently the most common commercial

production route. Similarly, PDLA may be produced from D-lactic acid monomers or DD-lactide dimers. However, the manufacturing cost of pure PLLA and PDLA homopolymers is very high, much higher than the cost of commercial PLAs (that are not made from pure L- or Dlactic acid monomers). Another type of PLA product, poly (D, L-lactic acid), PDLLA, can be obtained when DL-lactide cyclic dimers form the PLA backbone. Currently, low-cost commercial PLAs are copolymers of PLLA and PDLLA based on L-lactide and DL-lactide dimers, respectively, in which the molecules are rich in L-monomers, whereas D-monomers are involved as co-monomers [4,48]. Thus, the control of D-lactide content in commercial PLAs is used to control the PLA final properties. As in the case of other copolymers, higher co-monomer contents (i.e., D-content) lower the crystallization ability of PLA. It should be noted that PLA intrinsically exhibits slow crystallization rates, even in the case of PLLA with 0% D-lactide content [13]. It has been suggested that when Dmonomer content is above 10 mol%, PLA becomes fully amorphous [13]. Thereby, some of the important physical (e.g., optical transparency) and mechanical properties (e.g., strength and modulus) are significantly affected. The crystalline melting temperature (Tm) of PLA also varies as a function of D-lactide content. The lowering of Dlactide content does not only raise the PLA crystallinity, but it also raises its melting temperature, Tm, due to the increased molecular symmetry, which enhances the formation of crystals with more closedpacked structures. The maximum reported Tm of PLLA is in the range 175–180 °C, and as the D-lactide content increases Tm would decrease

Fig. 4. (a) Distribution and total number of studies reported on various PLA-based blends, and (b) distribution and numbers of articles on PLA-based ternary blend nanocomposites for various nanofillers.

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

313

Fig. 5. Stereochemistry configurations of lactic acid and lactide molecules [4,48].

by around 5 °C per 1% of D-content [13]. For instance, when the Dcontent is around 5%, Tm is about 150–155 °C, and when it further increases to 10%, the PLA is amorphous. Ding et al. [49] recently demonstrated that, under specific conditions, PLA with even 12 mol% Dlactide content could crystallize up to around 20% after gas-saturation and foaming due to the gas-/strain-induced crystallization. They reported crystals with Tm between 115 and 120 °C. In 1987, Ikada et al. [50] discovered that when PLLA is blended with PDLA another type of crystal structure is formed as PLLA and PDLA molecules co-crystallize together to form stereocomplex (SC) crystallites. These SC crystallites contain one PLLA and one PDLA molecule and the formed crystallites possess an extremely high Tm (~220–230 °C), which is around 50 °C above the melting temperature of PLA homocrystals. Existence of these crystals could strongly contribute to the final properties of PLA products [51–52]. There have been various reviews regarding PLA SC crystals by Tsuji [52–53], Fukushima and Kimura [54], and Jing et al. [55]. Therefore, in

this review we mainly provide an overview of the characteristics of PLLA/PDLA blends and the effects of SC crystals on the final physical and mechanical properties of the final blend products. 2.1. Crystallization behavior In order to differentiate the PLA SC crystals from its homo-crystals, wide-angle X-ray diffractometry (WAXD) and differential scanning calorimetry (DSC) are commonly used. In WAXD analysis, with a CuKα source, the PLA SC crystalline diffraction peaks appear at 2θ = 12, 21, and 24°, whereas for PLA α- and α′-homo-crystals they appear at 2θ = 15, 17, 19, and 22.5° (Fig. 6a) [52,56]. Fig. 6b also depicts the melting peaks of homo- and SC-crystals of PLLA/PDLA blends at different ratios. As noted, neat PLLA has a Tm around 180 °C, characteristics of homo-crystals, and SC-crystals exhibit a Tm around 230 °C [48]. The DSC heating or cooling thermograms can be used to estimate the amounts of homo- and SC-crystals by measuring the heat of fusion of

Fig. 6. (a) WAXD results of melt-quenched PLLA/PDLA blend films after annealing at different temperatures [52,57], and (b) DSC heating thermograms of PLLA/PDLA blends at different ratios [50].

314

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

the areas under the melting peaks. The degree of crystallinity of regular copolymer PLA samples may be calculated as: X c ð%Þ ¼

ΔHm −ΔHc 100 ΔH om ðPLAÞ

ð4Þ

where ΔHm and ΔHc are the melting and cold crystallization enthalpies, respectively, and ΔHmo(PLA) is 93.6 J/g, which is the melting enthalpy of 100% α-homo crystals of PLA copolymer [57]. The degree of crystallinity of PLLA/PDLA blend systems, however, can be measured as: Xc ð%Þ ¼

ΔH m1 þ ΔHm2 −ΔHc 100 ΔH om ðblendÞ

ð5Þ

where ΔHm1 and ΔHm2 are the melting enthalpies of α-homo crystals and SC-crystals, respectively; and ΔHmo(Blend) is the theoretical value for the melting enthalpy of 100% perfect crystals, including perfect αhomo crystals of PLLA (or PDLA) (ΔHm1o = 106 J/g) and SC crystals (ΔHm2o = 142 J/g) [58–62]. ΔHmo(Blend) varies with the relative amount of both α-homo-crystals and SC-crystals and can be determined as: ΔH om ðblendÞ ¼ ΔH om1 Xh þ ΔHom2 Xs

ð6Þ

where Xh and Xs are, respectively, the relative amounts of both types of homo- and SC-crystals. Each of these parameters can be measured from the enthalpy values as: Xh ¼

ΔH m1 ΔH m1 þ ΔH m2

Xs ¼

ΔHm2 ΔHm1 þ ΔH m2

ð7bÞ

Isothermal melt crystallization of α-homo crystals within spherulites has also been investigated via analysis of PLLA, PDLA, and PLLA/PDLA blends [63–65]. Spherulite growth in the blend occurs over a wider temperature range (≤180 °C) compared to the homopolymers (≤150 °C). In the blend case, the spherulite density is also higher than that for neat PLAs. This is because the SC-crystals present during isothermal melt crystallization play the role of nucleating agents and hence larger number of spherulite nucleation can be observed. However, in neat homopolymers, crystallization occurs via regular homogeneous crystal nucleation from the melt [63]. Schmidt et al. [64] and Yamane et al. [65] demonstrated how increased amounts of PDLA and thereby existence of larger contents of SCcrystals in the PLLA/PDLA blends could enhance heterogeneous αhomocrystal nucleation, with SC-crystals acting as nucleation sites. Yamane et al. also investigated how PDLAs with various molecular weights could influence the SC-crystal formation and, subsequently, the efficiency of α-homocrystal nucleation. They confirmed that low molecular weight PDLA isolated in the matrix of PLLA cannot form a stereocomplex crystallite with a surface area large enough to act as a nucleation site, whereas a high molecular weight PDLA chain can form a large stereocomplex crystallite with higher nucleation effectiveness. Impressive experimental observations by Maillard et al. [66] revealed that the SC-crystal structures in PLLA/PDLA 50/50 blend films are different from structures of blends that are rich in either PLLA or PDLA (Fig. 7). At a thickness of 50 nm (Fig. 7a and c), a triangular single crystal is observed and the global triangular shape does not depend on which polymer is the matrix. In the 50/50 blend, at the same film thickness (Fig. 7b), the structure remains hexagonal. At the film thickness of 20 nm, the crystals are necessarily dendritic, but their overall shape remains similar to the shape of the crystals formed in thicker films: hexagonal for the 50/50 ratio blend case and triangular for the blends rich in either PLLA or PDLA.

Fig. 7. Optical microscopy micrographs of various PLLA/PDLA blend films at different compositions isothermally crystalized at 200 °C. The film thicknesses are 50 and 20 nm for the top and bottom images, respectively [66].

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

2.2. Mechanical properties Mechanical properties of PLLA/PDLA miscible blends in the presence of SC-crystals have been investigated by Tsuji et al. [67–68], Sarasua et al. [60], and Srithep et al. [69]. In all these studies, the 50/50 PLLA/ PDLA blends were prepared and tested and the results were compared with those of the neat PLLA. Tsuji et al. showed that the tensile strength of the blends increased from ~22 MPa (for the neat PLLA) to ~45 MPa due to the presence of SC-crystals in the blends. Similarly, the modulus was reported to increase from ~1.1 to 1.5 GPa. The elongation at break was also increased from 2.2 to ~4.0% upon blending and formation of SC-crystals. The tensile strength, modulus, and elongation at break values of PLLA and PLLA/PDLA blends obtainedd by Sarasua et al. [60] were in the similar ranges of 70 MPa, 3.5 GPa, 2–3%, respectively. Accordingly, not only Sarasua et al. did not see any difference between the tensile properties of the neat PLLA and PLLA/PDLA blends, but their values were also quite different from those of Tsuji et al. [67–68]. Srithep et al. [69] showed that, upon blending, the tensile strength and modulus respectively decreased from ~44 to 19 MPa and 750 to 270 MPa, respectively, and the strain at break was significantly increased from ~6 to 235%. They explained that, when using a very low molecular weight PDLA as the blending polymer, the strength and modulus decreased and the ductility and toughness significantly increased. They also claimed that these results could be due to differences in the crystalline morphology (i.e., size and density of spherulites). 2.3. Rheological properties Rheological properties of PLLA/PDLA miscible blends in the presence of SC-crystals have been reported by Saeidlou et al. [70–71] and Wei et al. [72]. In the works of Saeidlou et al., blends with up to 10 wt% PDLA were melt processed and rheological properties were analyzed using rotational rheometry. For the first time, they monitored in rheometry the PLA SC formation kinetics at high temperatures. Frequency sweep tests performed on crystallized specimens showed remarkable increases in viscosity and elasticity of the blends as PDLA content increased above 3 wt%. They also confirmed that rheological percolation could be achieved at 4.5 wt% PDLA content based on the yield stress plot as a function of PDLA content. According to the increases in complex viscosity and storage modulus in the low frequency region, they also found that in the presence of a small concentration of PDLA, the chain microstructure was transformed from linear to branched architecture (i.e., network formation in the presence of SCcrystals). They also showed that for the blends with higher PDLA concentrations, the Newtonian plateau disappeared. For samples with a PDLA content of 3 wt% and larger, sharp increases of the viscosity

315

could be observed due to the formed network. The formed network would be generated by the rigid SC-crystal particles and the interparticle polymer chains, which are significantly restrained by the crosslinking effect of SC crystallites. Similar results were reported by Wei et al. [72]. 2.4. Degradation and permeability Tsuji et al. [57,73] investigated the effect of SC-crystals on the degradation behavior of PLA blends and water vapor permeability. Blends of PLLA/PDLA with 50/50 ratio were prepared and the results were compared with the neat PLLA and PDLA homopolymers. Based on thermal gravimetric analysis (TGA) at 250 °C, the remaining weights of the PLLA and PDLA films started to decrease immediately and monotonically to zero after 120 min and ~200 min, respectively. The lower weight losses in PDLA were due to PDLA possessing a higher initial molecular weight than that of PLLA. In the case of the PLLA/PDLA blend, the remaining weight started to decrease after 40 min and subsequently the decrease continued gradually to reach 23% after 200 min. The enhancement of thermal stability of the blend below 260 °C was attributed to the existence of SC-crystals. However, beyond 260 °C, where SC-crystals are melted, the thermal stability of the blend appeared to be similar to those of PLLA and PDLA. The formation of SC-crystals could decrease the water vapor permeability of PLA based films, whereas for the neat PLLA and PDLA films, the water vapor permeability is quite similar and larger than that of PLLA/PDLA. As shown, with the increase in crystallinity content in all three samples, the permeability further decreases continuously as the molecular crystalline structure becomes denser. 3. PLA binary blends with other biopolymers (bioblends) PLA is a biobased/biodegradable biopolymer. Other biopolymers could be biobased but not biodegradable (normally called biobased) and others could be non-biobased but biodegradable (normally called biodegradable). Research activities on blends involving the above three categories of biopolymers have been growing at a significant rate. Fig. 8 shows the frequency of studies conducted on binary PLA blends with other biopolymers as categorized above. These bioblends will be discussed in the following sections. 3.1. Blends of PLA with biobased and biodegradable polymers 3.1.1. PLA-Starch Starch is a polysaccharide derived from renewable resources and is biodegradable and biocompatible. It can be used as a filler or as a thermoplastic polymer in blends. Blends of PLA with starch have been

Fig. 8. Number of studies conducted on binary PLA blends with other biopolymers.

316

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

investigated in two main categories of PLA/natural starch and PLA/thermoplastic starch (TPS) [74]. The development of PLA/starch blends is of great interest for food packaging applications and could also be considered in biomedical applications. 3.1.1.1. PLA/natural starch. Jacobsen et al. [74] prepared PLA/natural starch blends. They also used poly (ethylene glycol) (PEG) to improve the toughness and ductility of PLA with the addition of natural starch particles. The addition of PEG enhances the crystallization of PLA and lowers its Tg, thus improving the processability of PLA with starch particles. Biresaw et al. [75] used contact angle measurements to determine the surface energies and interfacial tension of starch and several other polyesters including PLA. In 2003, Ke et al. [76] also studied blends with various starches and different amylose contents. It was shown that while water absorption increased with starch content [77], blends with high-amylose starch exhibited lower water absorption. They also showed that starch increased the crystallization rate and degree of crystallinity of PLA, while lowering its melting temperature [78]. Later on, Zhang et al. [79] also reported that starch behaved as a nucleating agent and increased crystallization rate of PLA, while it also improved elongation at break, but it had no effect on tensile properties. Park et al. [80] and Kozlowski et al. [81] incorporated polycaprolactone (PCL) and polyethylene glycol (PEG) as plasticizers to enhance the toughness and impact properties of PLA/natural starch blends that also suffered from low elongation at break and tensile strength. It was also shown that the starch particles acted as crystal nucleating agents in PLA and enhanced its crystallization rates [80]. Yu et al. [82] indicated that low molecular weight PEG had a larger plasticizing effect and increased the crystallization rate of PLA, although excessive plasticization reduced the water resistance, impact strength, tensile strength, modulus and the ductility of the final blend. On the other hand, high molecular weight PEGs yielded poor plasticization and the final blend properties could be deteriorated. They showed that a moderate molecular weight PEG could best enhance the properties of the PLA/starch blends. Jariyasakoolroj et al. [83] compared 3-glycidoxypropyl trimethoxysilane (GPMS), 3-aminopropyl trimethoxy silane (APMS), and 3-chloropropyl trimethoxysilane (CPMS) reactive compatibilizers and found that CPMS contributed more to enhance the compatibility of PLA and starch and thereby the tensile strength, modulus and ductility of the blends. Jun et al. [84] used toluene diisocyanate (TDI), isoporone diisocyanate (IPD), diethylene triamine, 1,6-diisocyanatohexane (DIH), and 4,4′-methylene diphenyl diisocyanate (MDI) as various reactive compatibilizers. They reported that DIH was more effective in improving the compatibility of PLA/starch blends and thereby their final properties. Xiong et al. [85] introduced epoxidized soybean (ESO) as a new biobased reactive compatibilizer for PLA/starch blends. They showed that in presence of ESO, the impact strength and elongation at break of the highly compatible PLA/starch blends improved up to 42 kJ/m2 and 140%, respectively. MDI [86–91], PLA grafted maleic anhydride (PLA-g-MA) [92–94], PLA grafted acrylic acid (PLA-g-AC) [95], PLA-grafted amylose (PLA-g-A) [96], PLA grafted glycidyl methacrylate (PLA-g-GMA) [97], tung oil anhydride (TOA) [98], hexamethylene diisocyanate grafted starch (HDI-g-starch) [99], dimer fatty acid (DFA) and dimer fatty acid polyamide (DFAPA) [100], dioctyl maleate (DOM) [101], triethyl citrate (TC) [89], and acetyl triethyl citrate (ATC) [93] have also been effectively used in several other studies as compatibilizers to improve the compatibility and hence the related properties in PLA/ starch blends. The degradation behavior of PLA/starch was also explored in a few studies. Gattin et al. [102] elucidated the biodegradation of PLA/starch blend in liquid, inert solid and composting media. The highest degradation rate was observed in a liquid medium, then composting medium and finally inert solid medium. Water absorption and enzymatic degradation of PLA/starch blends was also explored and it was shown that water sorption caused hydrolysis of PLA and leaching of starch particles from the PLA/starch interface. Enzyme (α-amylase) exposure resulted

in surface erosion and, thus, mechanical properties dramatically deteriorated [103]. Starch was also esterified by maleic anhydride and it was found that the decomposition rate of the blend with esterified starch was lower compared to the blend with native starch [104]. Thermal degradation of PLA/starch blends with lysine diisocyanate (LDI) and MDI was also investigated [105–106]. It has been reported that blends with diisocyanates enhanced the thermal resistance of the blends. Increased crystallinity did not have a significant effect on total degradation rate [107]. The flame retardancy of PLA/starch blends was also explored by Reti et al. and Wang et al. [108–109]. They used ammonium polyphosphate (APP) as a flame retardant agent and concluded that blends with starch showed a low limiting oxygen index (LOI). Several other research projects on PLA/starch blends based on novel approaches have been reported. Shen et al. [110] compared PLA/starch blends and ethanol supported systems for biological nitrate removal and microbial diversity. It was found that microbial diversity was better in PLA/starch blend system since the denitrification process was better in ethanol supported systems as ethanol was directly utilized by denitrifiers. In another study, Hwang et al. [111] elucidated the antioxidant release profile of neat PLA and PLA/starch films into ethanol solution in presence of α-tocopherol (α-TOC) and resveratrol as antioxidants. PLA/sugar palm starch bilayer films without any compatibilizer or additive for food packaging applications were also developed by Sanyang et al. [112]. Zhang et al. [113] used a pressure-induced flow (PIF) as a method to develop a layer-like PLA/starch blend microstructure and they found that impact strength was improved by 200%. Bolay et al. [114] also prepared PLA/starch blends without compatibilizer via cogrinding of both pellets in a tumbling ball-mill where the interactions between phases were significantly improved. 3.1.1.2. PLA/TPS. TPS or so called gelatinized starch is obtained by severe mixing at high temperature of starch with water and/or glycerol to destroy hydrogen bonds between starch granules and to restrict the reformation of crystals. Therefore, TPS possesses lower degrees of crystallinity than natural starch. Park et al. [115] prepared PLA/gelatinized starch blends and achieved improvements in toughness and elongation at break compared to PLA/natural starch. For starch gelatinization, they used various ratios of water/glycerol mixtures, and investigated their effect on starch gelatinization. They observed that the blend crystallization temperature decreased and starch acted as a crystal nucleating agent for PLA. The rheological properties of PLA/TPS blends were extensively investigated by Shin et al. [116] and they explained the relationship between the rheological properties of the blends and their morphology. Since 2007, several studies explored the effect of compatibilizers on the morphology and mechanical properties of PLA/TPS blends. PLA-gMA [117–121], MDI [122], formamide [123–124], peroxide [121], epoxidized cardanol [125], MA grafted PEG (MA-g-PEG) [126], and MA-gstarch [125,127], and PLA-g-starch copolymer [128] were extensively studied as compatibilizers, and it was shown that a more homogeneous morphology improved the mechanical properties and thermal stability of compatibilized PLA/TPS blends. Several other additives were incorporated in PLA/TPS systems as plasticizers. Citric acid, for instance, lowered the viscosity of PLA/TPS blends and a finer dispersion and lower interfacial adhesion were obtained [129]. Maleinized linseed oil was also used in different ratios to gelatinize starch [130]. Tween-60, linoleic acid and zein were used as starch plasticizers, and zein showed to be the more effective plasticizer; however, it lowered stiffness and strength while increasing ductility, crystallinity and processability of the PLA/zein plasticized TPS blends [131]. Diisodecyl adipate, diethyl adipate, ATC, acetyl tributyl citrate (ATBC) and tributyl citrate were also compared as plasticizers in PLA. It was reported that adipate esters, especially diethyl adipate, improved elongation, water vapor permeability, and processability of the blends more effectively [132]. Li et al. [133] compared glycerol, sorbitol and

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

glycerol/sorbitol mixtures as starch plasticizers. They observed that better mechanical properties and morphology were obtained in sorbitol plasticized starch/PLA blends with finer and more uniform TPS morphology within PLA. They also investigated the effect of a multifunctional epoxy-acrylic-styrene chain extender (CE) on the properties of PLA/TPS blends [134]. CE significantly increased the blend viscosity and its melt strength and hence the processability. It also improved ductility of the blend systems (up to ~340%). Wootthikanokkhan et al. [135] investigated the effect of processing conditions, via an internal mixer, on the properties of PLA/TPS blends. They showed that increases in temperature and time caused hydrolysis, which resulted in transesterification reactions in the blends and, consequently, increased the tensile strength and toughness. Phetwarotai et al. [136] studied the degradation of PLA/TPS blends in soil and they demonstrated that MDI as a compatibilizer increased the degradation rate and water absorptivity of the blends. 3.1.2. PLA-lignin Lignin is a highly aromatic coproduct of pulp and paper industries, and is after cellulose the most abundant biopolymer on Earth. Lignin resembles a highly cross-linked polyphenolic polymer without ordered repeating units [108]. It has an amorphous structure with varying Tg values [137–140] from 55 °C [137] to ~158 °C [139]. The lignin Tg varies depending on various modifications from ~127 to 158 °C and from ~ 105 to 125 °C, as reported in [139] and [140], respectively. Gordobil et al. [139] and Anwer et al. [141] showed that the addition of lignin to PLA could significantly increase the thermal stability of PLA, but suppresses its crystallization. They also showed that the mechanical properties of PLA/lignin decrease dramatically. The loss of mechanical properties of PLA with the addition of lignin is shown in almost all investigations [142–143]. Kim et al. [144] studied the effect of alkyl-chain modified lignin on PLA/lignin blend properties. They showed that part of the loss in mechanical properties could be recovered after modification of lignin chains. Later, Gordobil et al. [140] compared blends of PLA with Kraft lignin (KL) and acetylated Kraft lignin (AKL). They also showed that the esterification of the lignin (AKL) could compensate for some loss in mechanical properties in PLA/lignin blends, by increasing the lignin molecular weight and thermal stability. Lignin was also chemically modified through butyration to form ester functional groups in place of polar hydroxyl groups, which improved the miscibility of lignin with PLA [137]. 3.1.3. PLA-PHAs Polyhydroxyalkanoates (PHAs) are derived from renewable resources. They are also biodegradable. In comparison to other biopolymers, they offer great potential for packaging applications, especially food packaging, due to their good thermomechanical and barrier properties. Also, due to their bacterial origins, this class of polyesters shows good degradability characteristics. Therefore, PHAs have also been used in a number of biomedical applications, including tissue engineering, scaffolding, drug delivery systems, and resorbable surgical sutures [145–146]. Poly(3-hydroxybutyrate) (PHB) is a homopolymer of 3hydroxybutyrate and is the most common type of the PHA family. It has T g and T m of ~5 and 180 °C, respectively, with capability of cold crystallization during heating [147]. Another PHA copolymer is polyhydroxyvalerate (PHV). Since PHB exhibits high stiffness and crystallinity, it is often copolymerized with PHV to form polyhydroxybutyrate-co-valerate (PHBV) with improved flexibility and processability. Increasing the PHV content in PHB increases the ductility, reduces the stiffness, melting temperature, and crystallinity of PHB. Poly(3-hydroxybutyrate butyrate-co-3hydroxyhexanoate) (PHBHHx) is another copolymer of PHB with reduced crystallinity, broader processing window, higher flexibility, and lower tensile strength and modulus compared with PHB [145–146,148–149]. In order to develop a product with superior

317

mechanical and physical properties and good biodegradability for commodity (specifically food packaging) and biomedical applications, blends of PLA with PHAs have been investigated during more than two decades. These studies on blends of PLA with PHB, PHBV, and PHBHHx biopolymers are separately discussed in the sections below. 3.1.3.1. PLA-PHB. Several studies showed that PLA/PHB blends are miscible when low molecular weight (MW) PLA is used, but they are immiscible when the PLA MW is high [150–152]. The counterpart was also demonstrated later [153], showing that blending PLA with low and high MW PHBs resulted in miscible and immiscible blends, respectively. Zhang et al. [154] reported that solution-cast blends of PLA/PHB were immiscible, but melt blended cases turned out to be highly miscible. On the other hand, Kikkawa et al. [155] observed that melt prepared PLA/PHB blends were immiscible. The same group later claimed that the blends exhibited different phase structures, such as miscible, partially miscible, and immiscible, depending on the blending ratio and MW of the PHB [156]. According to their enzymatic degradation investigations, the degradation in the miscible blends proceeded faster than in immiscible and partially miscible blends. It was also shown that the hydrolytic degradation kinetics could be controlled by the molecular weight of the blending polymers [157]. On the other hand, Zhang et al. [158] concluded that PLA/PHB blends were immiscible, but highly compatible. Partial miscibility was also reported by Bartczak et al. [159]. The PLA crystallization was enhanced in presence of PHB with fast crystallization kinetics, and biodegradability improved with increasing PHB content. The role of PHB in accelerating the degradation kinetics was also shown by Musiol et al. [160]. Bartczak et al. [159] demonstrated how the ductility and impact strength of PLA could be improved up to 4 and 2 times, respectively, when blending with 20 wt% PHB. Few studies explored how different compatibilizers could influence the mechanical properties of PLA/PHB blends. To improve the impact strength and flexibility of PLA-PHB blends Dong et al. [161] used dicumyl peroxide (DCP) as a crosslinking agent, whereas Abdelwahab et al. [147] used Lapol 108 as a polyester plasticizer and Armentano et al. [162–163] incorporated an oligomer of lactic acid (OLA) as a plasticizer. Arrieta et al. in different studies [164–167] investigated the behavior of PLA/PHB blends with various plasticizers for food packaging applications. They showed that natural terpene D-limonene (LIM) as plasticizer raised the crystallinity of PLA and resulted in flexible films. They also showed that PHB played a reinforcing role in the PLA matrix and hence improved the oxygen barrier properties and surface water resistance. While PHB delayed the degradation of PLA, the addition of PEG and ATBC as plasticizers accelerated it. They also showed that catechin incorporation, as an antioxidant, enhanced the thermal stability of PLA and its release was improved by the addition of ATBC. Similar results were reported on the effect of ATBC on the mechanical and disintegration behavior of electrospun fibers of PLA/ PHB blends. Electrospun nanofibers of PLA/PHB blends were successfully developed by Nicosia et al. [168] for air filtration and antibacterial applications. PLA blends with a copolymer of PHB named poly(3-hydroxybutyrateco-4-hydroxybutyrate) (P(3HB-co-4HB)) were studied in [169–171] for packaging applications. The blends were found to be immiscible, but of high compatibility. The crystallization rate of PLA, the strain at break and biodegradability were improved in the presence of P(3HB-co-4HB). 3.1.3.2. PLA-PHBV. Iannace et al. [172–173] explored the properties of PLA/PHBV blends. They showed that PLA and PHBV were partially miscible, which caused a reduction of the crystallinity of PLA and of its degradation rate. It was also shown that the crystallinity of PLA could be improved due to the role of PHBV dispersed phase as crystal nucleating sites [174–175]. The partial miscibility or immiscibility with high compatibility were also confirmed by others [148,176–178]. It was also shown that PLA could hinder the crystallization of PHBV [176].

318

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

The rheological behavior of PLA/PHBV blends indicated that PHBV has extremely low thermal stability and suggested significant degradation during melt viscosity measurement [177]. The ductility and gas barrier properties of PLA/PHBV co-extruded multilayer films, for food packaging applications, were improved due to the generated layered structure [179]. Ma et al. [180] also showed that incorporation of 20 wt% PHBV with a high hydroxyvalerate content resulted in strain at break and impact strength of ~230% and 150 kJ/m2, respectively. Water and oxygen barrier properties were also shown to be improved significantly by the presence of PHBV [181]. Zinc acetate, a transesterification catalyst, was melt blended with PLA/PHBV blends to improve their miscibility and mechanical properties [182]; the transesterification reaction of PLA/PHBV suppressed the thermal decomposition of PHBV. The effect of compatibilization was further studied in presence of three types of different diisocyanates [183]. Compatibilization improved the overall mechanical performance, but it did not affect the thermal stability of the blend. Recently, Gonzalez et al. [184] revealed that the use of sepiolite in blends of PLA/PHBV increased the compatibility between the biopolymers, reduced the oxygen permeability, and increased the elongation at break. In another study, they also showed that the incorporation of diisocyanates enhanced the polymer blend compatibility, which led to an overall improvement in mechanical properties and more importantly resulted in a notable increase in the complex viscosity at low frequencies when compared with the same system without diisocyanates [185]. Cellulose fibers were also melt blended within PLA/PHBV blends which eventually could improve the stiffness, ductility and toughness simultaneously [186]. For biomedical purposes, it was shown that fibers of PLA/PHBV and PLA/PHBHHx blends have high biocompatibility and biodegradability [187]. Electrospun membranes coated with a conductive film were also explored by Chang et al. [188]. Porous PLA/PHBV electrospun fibers having potential applications in areas such as filtration, biomedical, and energy storage, were produced by Wagner et al. [189]. Li et al. [190] studied the production of PLA/PHBV fibers for textile applications. 3.1.3.3. PLA-PHBHHx. Few studies explored the behavior of PLA/PHBHHx blends [146,187,191]. The blends were reported to be immiscible with partial compatibility [146]. It was shown that the toughness of the blend films increased with 10 wt% of PHBHHx, although the blends underwent rapid physical aging, which caused significant toughness losses [191]. 3.2. Blends of PLA with biodegradable polymers 3.2.1. PLA-PCL PCL is a synthetic thermoplastic semi-crystalline aliphatic polyester, which is biodegradable and biocompatible with Tg and Tm of ~−60 and 60 °C, respectively. Contrary to PLA, PCL has a high elongation at break and toughness, although it has low tensile strength. Therefore, the development of PLA/PCL blends could improve the ductility and toughness of PLA, while raising the tensile strength of PCL. Due to their biodegradability and non-toxic properties, PLA/PCL blends have been proposed mainly for biomedical applications such as controlled drug release systems, tissue engineering, scaffolds, and transplants [192–193]. Also, due to the slow degradation rate of PCL (slower than that of PLA), PLA/PCL blends could control the life-time of a specific product. Within the last two decades, various studies have been conducted in the development and characterization of PLA/PCL blends. Tsuji et al. [194] studied blends of PLLA and PCL and their mechanical properties. In a later study [195], they extensively explored the hydrolysis and biodegradation behavior of films of PLLA/PCL blends in a phosphate-buffered solution. They showed that although both PLLA and PCL hydrolyzed and degraded very slowly (PCL was much slower), the addition of 25 wt% PCL significantly accelerated the hydrolysis of the blends and raised the degradation rate because of the increased

concentration of the terminal carboxyl groups. However, the hydrolysis was significantly retarded when 75 wt% PCL was employed. This was due to the water diffusion in the dispersed PLLA phase within the continuous hydrophobic PCL. Fukushima et al. [196] also studied the abiotic and biotic degradation of PDLLA/PCL blends. They found that the presence of the PDLLA phase catalyzed the degradation of PCL because of easier water diffusion into PCL domains through the PDLLA amorphous matrix. The crystallinity and miscibility of polymer phases, chemical structure, glass transition temperature of the polymers, temperature of the degradation medium, and the presence or absence of enzymes also affected the biotic and abiotic degradation. Liu et al. [197] investigated the enzymatic degradation of PLA/PCL blends in presence of proteinase K and Pseudomonas lipase. They showed that the resistance to enzymatic attacks in blends depended on the enzyme type and the use of amorphous or semi-crystalline PLA. The drug release behavior of PLA/PCL blends was investigated by Cai et al. [198]. It was demonstrated that a linear drug release behavior with time existed in PLA, whereas in PLA/PCL phase separation led to the generation of rough surfaces with high surface area and thereby high water sorption and, consequently, much faster drug release. Li et al. [199] showed that the lipase-catalyzed-enzymatic degradation rate decreased dramatically by increasing the PLLA concentration. Sivalingham et al. [200–201] showed that PCL had a better thermal stability than PLA and the addition of PLA did not affect either the thermal or enzymatic degradation of PCL. The degradation of PLLA/PCL membranes was also studied in phosphate buffer solution (PBS) by Gaona et al. [202]. The degraded PLA molecules exhibited faster crystallization rates due to the reduced molecular weight and enhanced molecular mobility, and the formed crystals made PLLA more resistant to hydrolysis. Despite Tsuji et al.'s and Fukushima et al.'s findings [194–196], membranes containing 20 wt% PCL underwent a slower degradation rate than the neat PLLA and PCL. Vieira et al. [203] measured the mechanical properties of PLA/PCL fibers during degradation. The decrease of tensile strength of PLA/PCL fibers followed the decrease of the molecular weight. Few studies explored the crystallization behavior of PLA/PCL blends. Kim et al. [204] showed that the increase of P(LA-co-CL) copolymer content reduced the crystallization rate of each PCL and PLA. On the other hand, Todo et al. [205], Simoes et al. [206], Noroozi et al. [207], Sakai et al. [208], Cock et al. [209] and Botlhoko et al. [210] found that the addition of PCL enhanced the crystallization rate and crystallinity of PLA, as dispersed PCL drops could behave as heterogeneous crystal nucleating sites for PLA. In this context, when the PCL droplets were evenly dispersed within PLA, the crystallization rate would even further improve with a more uniform spherulite morphology [210]. Newman et al. [211] found that the existence of chain interactions and partial miscibility lowered the melting and crystallization temperatures of PCL. Several studies explored the mechanical properties as well as the effects of using compatibilizers in PLA/PCL blends. Chen et al. [212], Rodriguez et al. [213], Todo et al. [205], Simoes et al. [206], and Urquijo et al. [214] confirmed that blending of PCL with PLA increased the elongation at break and toughness of PLA and deteriorated its tensile strength and stiffness. The effect of PCL-b-PEG block copolymer on the mechanical behavior of PLLA/PCL and PDLLA/PCL blends was showed by Na et al. [215]. They observed that a given content of copolymer could be a suitable compatibilizer in immiscible PLA/PCL blends and could lead to finer PCL droplet morphologies with improved ductility. Vilay et al. [216] also showed that the use of polyethylene oxidepolypropylene oxide-polyethylene oxide (PEO–PPO–PEO) as a triblock copolymer did not only increase the ductility and impact strength, but could also improve the stiffness and tensile strength of PLA. On the other hand, Gardella et al. [217] illustrated that PLA-g-MA as a compatibilizer in PLA/PCL blends could improve the elongation at break at an optimized content of PLA-g-MA while it also increased the stiffness of blends. In a few studies, the effects of the following reactive compatibilizers on the properties of PLA/PCL blends were investigated: lysine triisocyanate (LTI) [218–220], triphenyl phosphite (TPP) [221],

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

DCP [222], N,N′,N″-tricyclohexyl-1,3,5-benzene-tricarboxylamide (TMC-358) [223], GMA [224], functionalized polyhedral oligomeric silsesquioxane (POSS) [225], and epoxidized palm oil (EPO) [226]. The authors mostly indicated that the compatibility between PLA and PCL was improved, PCL droplet size was reduced and, consequently, the ductility and impact strength of the blends were improved. Rheological properties of PLA/PCL blends were also studied extensively by Wu et al. [227] and Noroozi et al. [207]. Using the Palierne model [228], they also determined the interfacial tension between PLA and PCL. Zhang et al. [229] further investigated the effects of applied shear rate on the morphological evolution of PLA droplets within PCL/ PLA blends (with PLA content of 30 wt%) while using the Palierne model to evaluate the droplet size and interfacial tension interrelationship. They confirmed that PLA droplet coalescence and breakup, occurred at low and high shear rates, respectively. Porous structures of PLA/PCL blends were explored in few studies [230–234]. Aslan et al. [230] and Calandrelli et al. [231] improved the homogeneity of porous membranes and scaffolds of PDLLA/PCL blends, while incorporating the random copolymer poly(D,L-lactide-co-εcaprolactone). Recently, Hunag et al. [234] used supercritical CO2 to generate porous scaffold based on the phase morphology control of co-continuous PLA/PCL blends. Prior to extracting PCL continuous phase, they annealed the samples in supercritical CO2. Being reported for the first time, their work allowed for the control of the pore sizes of the PLA from 50 to 150 μm, which means that the incorporation of CO2 could further control the scaffold structure. The barrier properties of PLA/PCL blends were studied by Jain et al. [235]. It was shown that the addition of talc decreased the PLA droplet size within the PCL matrix, and consequently improved the oxygen and water vapor barrier properties. Peponi et al. [236] also showed that the addition of nanosized hydroxyapatite increased the phase separation between PLA and PCL and more importantly induced an excellent thermally-activated shape memory response in blend of PLA/PCL with 30 wt% PCL content. 3.2.2. PLA-PBAT Poly(butylene adipate-co-terephthalate) (PBAT) is an aliphaticaromatic random copolymer that has high flexibility and toughness and, hence, it is an appropriate blending candidate for PLA to overcome its brittleness and low toughness. The Tg and Tm of PBAT are, respectively, ~−35 and 120 °C [237]. Jiang et al. [237], prepared immiscible blends of PLA/PBAT using a twin screw extruder. They demonstrated that the blend toughness and elongation at break increased with PBAT, although the tensile strength and modulus decreased. PBAT also accelerated the crystallization rate of PLA. Recently, Nofar et al. [238] revealed that, without the use of any compatibilizer, incorporation of 25 wt% PBAT in a high molecular weight amorphous PLA and with the use of a twin-screw extruder (TSE) PBAT droplet sizes below 1 μm within the PLA matrix could be achieved, and inceased the blend ductility up to around 265%. Deng et al. [239] also showed that when the PBAT content increasesd from 10 to around 20 wt%, the ductility of PLA/PBAT blend system dramatically increased from around 10 to 300%. Lee et al. [240] showed that the interfacial adhesion between PLA and PBAT was profoundly increased by applying ultrasound sonication. The effects of various additives as plasticizers or compatibilizers on the properties of PLA/PBAT have been investigated in several investigations. Coltelli et al. [241] illustrated that the addition of ATBC (up to 30 wt%) as a plasticizer could increase the strain at break of PLA/PBAT blend up to 300%. Al-Itry et al. [242–244] showed that the epoxybased Joncryl CE could increase the modulus, strain at break (up to 135%), and melt strength (i.e., strain-hardening) of the PLA/PBAT blends. Arruda et al. [245] showed that Joncryl increased the viscosity and reduced the PLA dispersed phase size within the PBAT matrix. Dong et al. [246] reported the effects of two CEs (Joncryl and 1,6hexanediol diglycidyl ether). The compatibility of PLA and PBAT were significantly increased by adding different CEs, and the strain at break

319

was enhanced up to ~500%, while not sacrificing too much the strength. This was due to the in-situ formation of PLA-co-PBAT copolymers in presence of CE. In another interesting study, Dong et al. [247] examined the influence of phthalic anhydride (PA) and bioxazoline (BOZ) as compatibilizers on mechanical and morphological properties of PLA/ PBAT blends. Small amounts of anhydride (PA) or bioxazoline (BOZ) increased elongation at break up to ~515% due to reduced domain sizes without affecting the tensile strength. Zhang et al. [248] showed that the use of GMA increased the surface adhesion between PLA and PBAT phases, enhanced the compatibility of the phases and, hence, the rheological properties. The strain at break was also increased up to 180% while not influencing the tensile strength. They also reported a 3times improvement of the impact strength. Nishida et al. [249] reported that the use of 2,5-dimethyl 2,5-di(tert-butylperoxy) hexane as a reactive compatibilizer reduced the domain size and, subsequently, increased the elongation at break up to 30%, but more importantly, the impact strength up to 30-times. Using the same compatibilizer, Coltelli et al. [250] showed that the blend viscosity increased with better surface adhesion of the phases and the elongation at break was enhanced up to 60%. Zhang et al. [251] reported that the incorporation of epoxyfunctional styrene acrylic as a reactive compatibilizer increased the impact toughness of the blends up to 3-times and elongation at break up to 150%. The use of DCP as reactive compatibilizer reduced the PBAT domain sizes, improved its interfacial adhesion with PLA, the melt strength and the elongation at break increased to ~300% while the tensile strength remained unaffected [252–253]. Lins et al. [254] showed that phosphonium ionic liquids as new compatibilizers decreased the PLA domain sizes and enhanced its uniformity in a PBAT matrix, and hence increased the modulus of the PBAT. It has also been shown that when using ethylene-methyl acrylate-glycidyl methacrylate (EMA-GMA) copolymer as a compatibilizer, a super-tough PLA/PBAT/EMA-GMA multicomponent blend (75 wt%:10 wt%:15 wt%) could be obtained with improved notched impact strength of around 62 kJ/m2, which is about 13 times larger than that of a PLA/PBAT binary blend containing10 wt % PBAT [255]. The melt rheological properties of PLA/PBAT blends were studied by Gu et al. [256]. They showed that the storage modulus of the blend increased with PBAT content at lower frequencies, due to the appearance of the PLA/PBAT interface contribution [256–257]. Nofar et al. [258] investigated the rheological and interfacial properties of PLA/PBAT with fixed weight ratio of 75/25, while also using different processing techniques and two different Mw PLAs for the blend preparation [259]. Using the Palierne model [228] they calculated the interfacial tension between PLA and PBAT to be ~1.2 mN/m. They also confirmed that under shear flow, PBAT droplet coalescence could occur and be monitored by rheometry and that the effect of coalescence could be predicted using the Palierne model. Also using the Palierne model, Jalali Dil et al. [260] found that the interfacial tension between PLA and PBAT could be as low as 0.6 mN/m when a low Mw PBAT was dispersed in PLA. The crystallization behavior of PLA/PBAT blends was studied for systems with different compositions [261–265]. The crystallization rate of PLA was enhanced in the presence of PBAT droplets, which also led to an increase in the degree of crystallinity. The Tm of PLA decreased with increasing PBAT ratio, which might be due to the reduced degree of PLA crystal perfection or partial miscibility between PLA and PBAT (confirmed by the Tg reduction of PLA in the blends) [261–262]. Quero et al. [263] showed that ATBC behaved as a plasticizer and increased the overall crystallization rate of PLA/PBAT blends. In contrast, Wang et al. [264] showed that the use of tetrabutyl titanate (TNBT) as a compatibilizer reduced the PLA crystallization rate due to transesterification. Chiu et al. [265] showed that heat treatment increased the crystallinity of PLA and, thereby, the tensile modulus and strength. Signori et al. [266] investigated the thermal degradation of PLA/PBAT blends upon melt processing. In immiscible blends of PLA/PBAT, the degradation occurred through transesterification. Although the degradation could affect properties such as melt viscosity, the generation of

320

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

PLA/PBAT copolymer via transesterification could reduce the interfacial tension between PLA and PBAT and, thereby, the PBAT domain size could be reduced due to the increased compatibility resulting from the transesterification reaction. Weng et al. [267] explored the biodegradation of PLA/PBAT blends and those of the neat PLA and PBAT under soil conditions. In a recent study Liewchirakorn et al. [268] explored PLA blends with PBAT to fabricate peelable lidding films. They showed that PLA/PBAT (80/20) blend revealed desired optical and peel–seal properties with a haze b10% and low peel strength in an easy-peel characteristic. 3.2.3. PLA-PBSA Poly(butylene succinate-co-adipate) (PBSA) is an aliphatic and random co-polyester that, similar to PBAT, has a high ductility and impact strength, good thermal and chemical resistance, and high processability. The Tg and Tm of PBSA are, respectively, ~−45 and 90 °C. The first study on immiscible PLA/PBSA blends was probably conducted by Lee et al. [269]. They showed that the addition of PBSA improved the impact strength of PLA while decreasing the tensile strength and modulus, and interestingly having no effect on the elongation at break. Similar results were also obtained by Pivsa-Art et al. [270]. Ojijo et al. [271] showed that 30 wt% PBSA could raise the elongation at break by only 6%. Nofar et al. [238], however, showed that the elongation at break of the blends with 25 wt% PBSA could be improved by 150% when prepared in an internal mixer with a given mixing time. The use of compatibilizers in PLA/PBSA blends has been explored by few researchers. Using octavinyl POSS (vPOSS) and epoxy cyclo hexyl POSS (ePOSS) as compatibilizers for PLA/PBSA, Wang et al. [272] showed that both POSSs increased the crystallization rate of PLA while only ePOSS improved the rheological properties of the blends. Eslami et al. [273] also reported enhancements in melt strength and strain hardening by using Joncryl epoxy-based CE in a single composition (70/30) of PLA/PBSA blends. Ojijo et al. [274] claimed that super toughened PLA/PBSA blends were manufactured via in-situ reactive compatibilization using Joncryl epoxy-based CE. The elongation at break of the PLA/PBSA blends with chain extender increased up to 200% while the impact strength increased 8 times. In another study, Ojijo et al. [275] revealed that TPP as a compatibilizer significantly reduced the PBSA domain sizes and, consequently, improved the impact strength (~3 times) and elongation at break (up to 200%). Gui et al. [276] investigated the rheological properties of PLA/PBSA blends. While the blend showed shear-thinning behavior, the storage modulus increased at low frequencies in the blend samples due to the interfacial contribution. Further, the blends exhibited longer relaxation time accordingly due to the shape relaxation of the droplets. The calculated interfacial tension between PLA and PBSA was high, in the range of 5.3–6.1 and 3.8–5.2 mN/m using weighted relaxation spectra and the Palierne model [228], respectively. In contrast, Nofar et al. [258] obtained using the Palierne model an interfacial tension between PLA and PBSA as low as ~1.5 mN/m. Eslami et al. [277] reported that the addition of PBSA induced a strain-hardening behavior, more pronounced as the PBSA content increased. 3.2.4. PLA-PBS Poly (butylene succinate) (PBS) is a biodegradable aliphatic polyester whose properties are comparable to PP. PBS possesses high flexibility, excellent impact strength, thermal and chemical resistance and good processability; hence, it can be a good candidate for blending with PLA. It is a biopolymer with Tg of ~−35 °C and Tm of ~114 °C [278]. The miscibility between PLA and PBS has not yet been entirely elucidated. Park et al. [279–280] investigated the morphology and miscibility of PLA/PBS blends with different compositions prepared using melt mixing. Using differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), and small angle X-ray diffraction (SAXS) techniques, they found that the blends were only miscible in their amorphous states and two distinct melting peaks of PLA and PBS existed

without any co-crystallization between the two polymers. On the other hand, the negative value of the Flory–Huggins interaction parameter indicated full miscibility. Bhatia et al. [281] used modulated DSC to measure the Tg and reported that the blends were immiscible, although their rheological results revealed partial miscibility between PLA and PBS when the PBS content was below 20 wt%. Yakohara et al. [282] also revealed that the PLA/PBS blends were immiscible and the interfacial tension between PLA and PBS was determined to be ~3.5 mN/m using the Palierne model. Under similar condition, a value of 3.7 mN/m was also reported by Xu et al. [283]. Wu et al. [284] also claimed that PBS and PLA were thermodynamically incompatible and immiscible, and determined via the Palierne model an interfacial tension at 190 °C of ~1.1 mN/m. Deng et al. [278] also demonstrated that PBS was not miscible with PLA even at 20 wt% of PBS. Yakohara [282], Wang [285], and Deng [278] found that the PLA crystallization improved in presence of PBS due to either a lubrication effect of PBS molten phase during melt crystallization, or nucleating ability of PBS during cold crystallization of PLA. Researchers attempted to improve the ductility, toughness, and impact properties of PLA by blending with PBS. Bhatia et al. [281] found no improvement in the strain at break in PLA/PBS blends. On the other hand, Deng et al. [278] obtained an over 250% improvement in ductility with only 10 wt% PBS, which was due to a generated PBS fibril phase morphology. Other authors investigated the incorporation of compatibilizers to improve the toughness of PLA/PBS blends. Shibata et al. [286] blended PLA with poly(butylene succinate-co-l-lactate) (PBSL) and it was found that the structural differences between PBS and PBSL had surprisingly slight effects on the compatibility with PLA. Wang et al. [285] reported that when DCP was added in blends with 20 wt% PBS, the impact strength and strain at break of the blends were significantly improved with values of ~30 kJ/m2 and 250%, respectively. Ji et al. [287] also used DCP, which enhanced the compatibility between PLA and PBS due to the formation of a PLA–PBS copolymer. In blends with 20 wt% PBS, the addition of DCP increased the strain at break from 50% to ~200%, while also increasing the tensile strength from 55 to ~80 MPa. Harada et al. [288] also demonstrated that the use of 0.5 wt% LTI as a compatibilizer improved the impact strength of PLA/PBS blends with 10 wt% PBS from ~18 kJ/m2 up to ~70 kJ/m2. The melt flow index (MFI) also decreased from 25 to ~3 g/10 min at 200 °C. Persenaire et al. [289] showed that the use of PLLA-g-MA as a reactive compatibilizer increased the strain at break of blends with 20 wt% PBS, from 240% to ~390%, while also improving the tensile strength. Li et al. [290] reported that cross-linking with MDI significantly improved the elongation at break of blends up to 290%. Poly(butyl succinate-colactic acid), p(BS-co-LA), random and block copolymers were synthetized and were then utilized as compatibilizers in PLA/PBS blends. Although the addition of the noted copolymers reduced the final crystallinity of the blends, only the use of the P(BS-co-LA) block copolymer could compatibilize the PLA and PBS and somewhat increased the elongation at break and the impact strength of the blends [291]. Biocompatibility of PLA/PBS blends was also explored by Kun et al. [292] and Kimble et al. [293]. They reported that PBS/PLA blends have comparatively satisfactory in vitro and in vivo biocompatibilities. Moreover, blends of PLA/PBS exhibited a ductile behavior with gradual losses of strength and modulus as they biodegraded.

3.2.5. PLA-PVAc Polyvinyl acetate (PVAc) is a synthetic and hydrophilic polymer. PVAc can be used to commercially produce polyvinyl alcohol (PVOH) by hydrolysis [294]. Gajria et al. [295] reported that PLA/PVAc form a miscible blend, as confirmed from the Tg values. Elongation at break of PLA could be improved with PVAc. Addition of PVAc also dramatically decreased enzymatic degradation rate of PLA. Mahalik et al. [296] used Novozyme 435 and Lipolase enzymes with different solvents for investigating enzymatic degradation of PLA/PVAc blends. The most suitable

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

solvent was shown to be toluene and reduction in degradation rate occurred for both Novozyme 435 and Lipolase. 3.2.6. PLA-PVA or PVOH Poly(vinyl alcohol) (PVOH) is a biodegradable, biocompatible, inexpensive, hydrophilic and highly flexible polymer [297]. Shuai et al. [297] prepared PLA/PVOH blends and indicated that PLA/PVOH blends were immiscible, but for low PLLA contents some degree of compatibility was observed due to inter-polymer hydrogen bonding. Tsuji et al. [298] reported that PLLA/PVOH blends had higher water absorption capacity compared to neat PLLA and neat PVOH due to increased interfacial area between PLLA-rich phase and PVOH-rich phase. Yeh et al. [299] depicted that PVOH behaved as a nucleating agent in blends for PLA crystallization. Li et al. [300] synthesized a new plasticizer, lactiglyceride, by esterification of L-lactid acid and glycerol. They used it to plasticize the PVOH, and, then, prepared PLA/PVOH blends in the presence of stannous octoate (Sn(Oct)2) as a catalyst. It was found that lacti-glyceride behaved not only as a plasticizer, but also as a compatibilizer for PLA/PVOH blends as it improved toughness and tensile strength. Tran et al. [301] successfully prepared PLA/PVOH blend filaments by melt spinning for several textile techniques like knitting, weaving, braiding, or stitching. 3.2.7. PLA-EVOH Ethylene vinyl alcohol (EVOH) is a semi-crystalline and biocompatible thermoplastic copolymer. Both hydrophilic alcohol groups and hydrophobic vinyl units are found in the EVOH chain. It has good barrier properties and high resistance to oil. Due to these characteristics, it is widely used as packaging materials [302]. Lee et al. [303] prepared PLA/EVOH blends and PLA-g-EVOH graft copolymer by reactive blending with TNBT as a catalyst. They found that copolymerization improved mechanical properties and resistance to microbial attacks far better than for PLA/EVOH blends. Zhang et al. [304] used an epoxybased Joncryl CE alone or with zinc stearate (ZnSt2) as a reactive compatibilizer to enhance transparency of PLA/EVOH blends. Blends with Joncryl/ZnSt2 showed a more uniform size distribution of EVOH drops and enhanced transparency due to a significant reduction in light scattering and improved water vapor barrier properties. Gui et al. [305] also reported that upon increasing EVOH, water vapor and oxygen barrier properties of PLA were enhanced. Wu et al. [306] reported that the use of poly[(ethylene)-co-(methyl acrylate)-co-(glycidyl methacrylate)] (PEMG) as a CE increased the thermal resistance of PLA/EVOH blends and retarded their degradation. 3.2.8. PLA-PPC Poly(propylene carbonate) (PPC) is an amorphous biodegradable aliphatic polycarbonate with a similar chemical structure to that of PLA and has a Tg between 25 and 45 °C. Ma et al. [307] suggested that PLA and PPC were partially miscible and compatible to some extent because of the similarities in their chemical structures. They showed that at a PLA/PPC blending ratio of 60/40 phase inversion occurred and a cocontinuous morphology was formed. This was also confirmed by Gao et al. [308]. At this blending ratio, the influence of carbon black (CB) on electrical conductivity improvements was also investigated. The percolation threshold for the electrical conductivity was lowered in the blend systems when CB was mainly dispersed within PPC due to its lower processing viscosity [309]. Interestingly, Yao et al. [310] showed that the addition of 0.9 wt% MA into the PLA/PPC (70/30) blends improved the toughness by 1355% while maintaining the strength. This was due to the reduced PPC domain sizes and increased interfacial interaction between PLA and PPC. However, higher MA contents decreased the strength and increased the toughness, indicating an obvious plasticizing effect. Gao et al. [311] also proved that the addition of a homopolymer PVAc significantly improved the compatibilization of partially compatible/miscible PPC/PLA blends and refined the PLA/PPC blend morphology by selectively being localized at the interface of the two

321

phases. The interface-localized PVAc also acted as a bridge to enhance the interfacial bonding, which was mainly responsible for the significant increase in the mechanical properties. The addition of 1,2-propanediol isobutyl POSS (P-POSS) also showed a profound enhancement of the compatibilization between PLA and PPC and thereby improved tensile and impact strengths [312]. Zhou et al. [313] explored the effect of catalytic transesterification using TNBT as a catalyst in PLA/PPC blends. TNBT promoted the transesterification between PLA and PPC, which significantly increased the elongation at break when the PPC was the matrix. 3.2.9. PLA-PES Poly(ethylene succinate) (PES) is a biodegradable semicrystalline polyester, which has high strain at break and flexibility. Therefore, it can be a candidate for blending with PLA to remedy its brittleness and low toughness issues [314]. Lu et al. [315] and Fan et al. [316] found that the addition of PES increased the crystallinity and elongation at break of PLA. It was also shown that the crystallization rate of PLLA was accelerated by the addition of PES, while no change was observed in the crystallization mechanism. 3.2.10. PLA-PGA Poly(glycolic acid) (PGA) is a linear aliphatic polyester widely used in the biomedical field due its biodegradability, biocompatibility and good mechanical properties [317]. You et al. [318] prepared nonporous ultrafine PLA/PGA fibers by electrospinning. They observed that the degradation rates of non-porous ultra-fine PGA/PLA fibers decreased with increasing content of PLA due to the slower degradation rate of PLA than PGA. In another study, they prepared porous PLA/PGA fibers with co-continuous morphology also by electrospinning. Subsequently, they removed PLA phase by dissolution with chloroform and interconnected pores were obtained after PLA extraction [319]. Pandey et al. used microwave irradiation technique to increase the compatibility and miscibility of the PLA/PGA blends. They found that a microwave treatment induced crosslinking or esterification, but no significant effect on physical properties of the blends was observed [320]. 3.3. Blends of PLA with biobased polymers In recent years, there has been a great interest in producing biobased polymers (even if non-biodegradable) due to public and environmental concerns. For this purpose, plants, wood, and other biomass resources are commonly used [321]. Bio-based polyamide (PA), polyethylene (PE), and PET are among the most known bio-based non-biodegradable polymers, which have been investigated. So far a few research activities on PLA blends with these polymers have been reported. For instance, there are some studies about bio-based PET derived from bio-based ethylene glycol mainly for packaging purposes, but these do not include properties of its blends with PLA [322]. Bio-based polyamides (PAs) are coded as PA610, PA1010, PA1012, PA11 and PA12 [323]. Zhang et al. [324] investigated the shape memory effect of PLA/PA12 (elastomer PAE) blends. Upon blending 10 wt% PA12 with PLA, the elongation at break increased to ~195% and thermal recovery process showed the blends had a shape memory behavior. Stocklet et al. [325] elucidated the morphology, thermal and mechanical behavior of PLA/PA11 compatible blends. They showed that changes in PA11 content did not affect the mechanical properties significantly. However, toughening effect of PA11 on PLA was observed due to the strong interfacial adhesion between PLA and PA11. Few studies explored the effects of compatibilizers such as titanium isopropoxide [326], p-toluene sulfonic acid [327], polyether-b-amide (PEBA) [328], and PEO [329–330] on properties of PLA/PA11 blends. Some of these investigations [326–328] suggested that compatibilizers played an important role on enhancing the compatibility and impact strength of the blends due to the ester-amide interchange reaction. Heshmati et al. [329–330] also illustrated that the addition of 5 wt% of PEO as a plasticizer of PLA/PA11

322

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

blends significantly reduced the interfacial tension values between the immiscible PLA and PA11 components. The mechanical properties of the ternary PLA/PA11/PEO blends were found to be strongly dependent on the added PEO concentration and in a co-continous blend of PLA and PA11, the addition of maximum 15 wt% PEO significantly increased the impact strength and ductility of the blends [329–330]. Pai et al. [331] prepared PLA/PA610 blends from biomass. They used epoxy resin as a reactive compatibilizer, which could enhance the interfacial adhesion and impact strength of the blends. The epoxy resin reacted with both polymers, and formed PLA-co-epoxy-co-PA 610 copolymer at the interface of the two phases. Up to an optimum level, the use of compatibilizer reduced the interfacial tension, hence the dispersed phase domain sizes, and increased the tensile, flexural, and impact strengths. Pai et al. [331] claimed that when the amount of epoxy resin was beyond a critical level, cross-linking could occur and the dispersion of the PA phase could be hindered by the increased viscosity, thus causing deterioration of the impact strength. Kakroodi et al. [332] compared blends and microfibrillated composites (MFCs) of PLA with PA610 as well as PA1010 for packaging applications. They showed that the fibrillation significantly improved the crystallization kinetics and gas barrier properties of PLA. Bio-based PE (BioPE), derived from sugar cane [333], was also blended with PLA by Brito et al. [334]. They used ethylene-glycidyl methacrylate (E-GMA) and EMA-GMA copolymers as compatibilizers and showed that the droplet sizes and distribution of PE were not significantly affected by either E-GMA or EMA-GMA, but the impact strength was larger in blends containing EMA-GMA. However, the increase in elongation at break was much more pronounced in blends with E-GMA.

4. PLA binary blends with synthetic/nondegradable thermoplastics Manufacturing of PLA-based binary blend systems with synthetic/ noncompostable thermoplastics and elastomers has also been explored because the development of such partial bioblends could also be beneficial from environmental and energy considerations. The majority of the investigations on these topics have been carried out since a decade ago, whereas the oldest studies belong to less than two decades ago. Fig. 9 presents the number of these studies as a functions of the blending polymer. As seen, a large number of these investigations relates to PLA/ rubber and PLA/polyurethane (PU) blends, as rubber and PU may provide high ductility and toughness to PLA. This section reviews the studies conducted on blends with synthetic/noncompostable thermoplastics, and Section 5 will discuss the blends with elastomers.

4.1. PLA-PE The main investigations on PLA/PE blends have been initiated in 2001. The use of PE for blending with PLA is mainly due to its low cost and high commercial value. Among PE types, low density PE (LDPE) and linear LDPE (LLDPE) have been mainly utilized due to their higher toughness and better impact performance [335]. Binary blends of PE and PLA are immiscible due to their high interfacial tension originating from the differences in their molecular chemistry. Therefore, the PLA/PE blends inherently possess poor mechanical properties; hence, the use of compatibilizers is inevitable to reduce the interfacial tension and thereby the domain sizes, and, consequently, to increase the morphological stability and interfacial adhesion. Wang et al. [336] synthesized PE-PLA diblock copolymer (PE-b-PLLA) as a compatibilizer. They showed that the addition of PE-b-PLLA to PLA/PE (80/20) blends, through solution blending, reduced the PE domain size from ~35 to 1.7 μm with a more homogenous distribution. As a result, the ductility and toughness were improved by a factor N3 and impact strength by over 10 folds in magnitude. Anderson et al. [337–338] used melt blending in conjunction with two different PE-b-PLLA copolymers with short or long PLA blocks. They found that the use of copolymer with longer PLA block segments was necessary to reduce the LLDPE domain size from ~4.3 to 0.9 μm within an amorphous PLA. This allowed them to raise the impact strength from ~36 to 460 J/m. Within a semicrystalline PLA as the matrix, significant toughening (~510 J/m) was observed even in the absence of a compatibilizer whereas the use of copolymers slightly reduced the drop size from 1.9 to 0.9 μm and, hence, improved the impact strength to ~660 J/m. They also explored the interfacial adhesion of PE with a semicrystalline PLA using various PE types. When using a more rubbery PE (LLDPE), a strong interfacial adhesion improved the toughness, whereas when using a stiff PE (HDPE), weakest adhesion was beneficiary for impact strength. Kim et al. [339] showed that the use of PE-GMA as a reactive compatibilizer could react with PLA and reduce the domain size of LDPE to ~0.5 μm, and consequently improved the mechanical properties of the immiscible blends. When polyoxyethylene (POE) was also added into PLA/LLDPE blends, according to the spreading coefficient, POE would spread on LLDPE extensively to completely encapsulate LLDPE and would chemically react with PLA. Thus, the interfacial adhesion significantly improved and thereby the toughness of the ternary blend with PE drop sizes of b0.5 μm was enhanced [340]. The use of LDPE-g-MA as a compatibilizer also improved the interfacial interactions and caused improvements in mechanical and thermal properties of PLA/LLDPE [341–342]. Djellali et al. [343] used copolymer ethylene-co-GMA (EGMA) as a compatibilizer and they showed that the epoxy groups of

Fig. 9. Number of studies on PLA blends with synthetic/nonbiodegradable thermoplastics/elastomers.

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

EGMA and carboxylic or hydroxyl groups of PLA reacted. The interfacial adhesion, as a consequence, improved with reduced domain sizes of either PLA or PE, which significantly enhanced the ductility and impact strength of the final blends. The properties of metallocene filled PE (mPE)/PLA blends containing an ethylene–GMA–vinyl acetate (EGMA–VA) compatibilizer, were investigated Lai et al. [344]. The addition of compatibilizer enhanced the interactions between the mPE matrix and dispersed PLA and the cold crystallization of PLA was completely slowed down. Synergistic effects by compatibilization and annealing also improved the tensile strength and modulus due to the increased PLA crystallinity. Recently, Zolali et al. [345] revealed that the addition of EMA-GMA to the cocontinuous blend of PLA/LLDPE significantly reduced the cocontinuous phase thickness from around 25 to 5 μm, which generated a supertough blend with impact property of 515 J/m, 13 times and 32 times greater than the cocontinuous PLA/ LLDPE blend and PLA, respectively. Thurber et al. [346] accelerated the reactive compatibilization of PLA/PE blends by localizing stannous octoate catalyst at the interface of two phases, which resulted in a much finer droplet morphology (b1 μm) with enhanced interfacial interactions. Blends of PLA with HDPE were also studied by Lu et al. [347] and the phase compatibility was significantly improved with the addition of ethylene-butyl acrylate-GMA (EBA-GMA). Hamad et al. [348–349] studied the melt rheology of PLA/LDPE blends and showed that they exhibited shear-thinning behavior. Jiang et al. [350] showed that morphology variation, by using various screw configurations of a twin-screw extruder, could influence the rheological properties of PLA/LDPE blends. The blends processed through shear/ chaotic mixing showed finer PE domain morphology with increased viscoelastic properties. The presence of PE domains accelerates the crystallization rate and degree of crystallinity of PLA, as PE acts as a nucleating agent [351]. Bee et al. [352] showed that irradiation-induced cross-linking in PLA/ LDPE improved the mechanical properties and crystallinity by promoting a highly ordered rearrangement of the matrix molecules. Thermal degradation investigation of PLA/LLDPE blends showed that LLDPE had no effect on the feedstock recycling of PLLA [353]. The reinforcing effects of adding PLA into LDPE were also confirmed by Rezgui et al. and Hamad et al. [349,354–355]. As expected, they showed reductions in ductility and toughness, whereas the strength and stiffness were improved. 4.2. PLA-PP Reddy et al. [356] illustrated that the hydrolysis resistance, biodegradability, and dyeability of PLA fibers improved when PLA was blended with PP. They also showed that PLA and PP had partial compatibility due to the better alignment of molecules during fiber drawing. Generally, blending PLA and PP generates immiscible morphologies and the mechanical properties would be determined by the high tensile and flexural strength and modulus of PLA and the high ductility and toughness of PP [357–358]. The majority of studies dealt with the use of compatibilizers to improve blend properties [358–365]. With PP as the matrix, Chen et al. [359] showed that the decrease in PLA domain size in the presence of PP-g-MA improved the rheological properties of the blend. In another study [361], two different compatibilizers were used in PP/PLA (80/20) blends, and the properties were explored before and after hydrolysis. Incorporation of 3phr PP-g-MA copolymer as a compatibilizer, the tensile strength of the blends before hydrolysis was maximized, whereas after hydrolysis the tensile strength did not change with PP-g-MA content. For blends with styrene-ethylenebutylene-styrene-g-MA (SEBS-g-MA), the tensile strength before or after hydrolysis decreased continuously. Using the Palierne and ChoiSchowalter models, the interfacial tension of the PP/PLA (80/20) blend was shown to be minimum at a PP-g-MA content of 3 phr. The impact strength, however, markedly increased with SEBS-g-MA. This increase was more significant after hydrolysis due to the possible reduction of

323

the PLA brittleness after hydrolysis. The same group of investigators [362] compared the effects of PP-g-MA with two other compatibilizers, namely, PE-g-MA, and PP-g-MA/PE-g-MA hybrid mixture. The tensile, flexural, and impact strengths, before and after hydrolysis, were more effectively increased with the hybrid compatibilizer than with the single compatibilizers. The morphology was also much finer in the hybridcompatibilized blend. PLA, as the matrix, was also melt blended with PP using PP-g-MA and GMA as reactive compatibilizers [363]. Contrary to GMA, that had a negative effect, the use of PP-g-MA enhanced the compatibility of the polymers, reduced the PP domain size, and even improved the thermal stability of PLA. The use of EGMA−methyl acrylate terpolymer (PEGMMA) as a compatibilizer also enhanced the interfacial adhesion between PLA and PP, lowered the interfacial tension, reduced the domain sizes, and significantly improved the ductility, toughness, and rheological properties of the PLA/PP compatibilized blends [364]. 4.3. PLA-PS Due to its importance in blend manufacturing, the interfacial tension between PLA and PS was studied by Biresaw et al. [366] using the imbedded fiber retraction (IFR) method. In the 170–200 °C temperature range, the interfacial tension had a value of around 5.4 mN/m and the values were independent of temperature. Luciani and Antonoff's equations predicted similar values (4.4 and 3.0 mN/m, respectively), whereas geometric and harmonic mean equations predicted lower values of 1.1 and 1.7 mN/m, respectively. Sarazin et al. [367] showed how the extraction of PS from a co-continuous blend of PLA/PS could generate a porous structure of PLA for biomedical applications. They showed that the use of PS-b-PLLA diblock copolymer compatibilizer further narrowed the co-continuous channels and hence decreased the pore size of the final porous materials. The same group also showed that annealing time and temperature could coarsen the co-continuous channels and the final morphology. The use of diblock copolymer, however, not only refined the co-continuous morphology but also hindered the coarsening of the structure [368]. The morphology coarsening of PLA/PS co-continuous blends that occurred through phase segregation during annealing was also extensively analyzed by Leung et al. [369–370]. Recently, PLA/PS blends were reactively compatibilized using the oxazoline-carboxylic acid reaction and then were blended with PE. The oxazoline functionalized PS was then extracted and porous PLA with a bimodal pore size distribution was obtained [371]. Biresaw et al. [372] studied the tensile behavior of PLA/PS blends at different ratios. The properties were averaged at various PLA/PS blending ratios. Mohamed et al. [373] studied the thermal behavior of PLA/PS blends at different ratios and confirmed the immiscibility of the blends and the thermal stabilization of PLA when blended with PS. On the other hand, Zuza et al. [374] claimed complete miscibility of PLA/PS blends by incorporating hydroxyl (–OH) groups on PS through copolymerization with hydroxyl-styrene. It was confirmed that the PLA/PS blends showed a shear-thinning behavior [375–377]. 4.4. PLA-ABS Acrylonitrile-butadiene-styrene (ABS) copolymer has a structure similar to that of high-impact PS (HIPS). It consists of a rubbery polybutadiene (PB) dispersed in a rigid styrene-acrylonitrile (SAN) matrix. ABS is used as impact modifier and toughening agent for many engineering plastics for applications such as in the automotive field. Li et al. [378] studied the blends of PLA/ABS. PLA and ABS proved to be thermodynamically immiscible, which caused the deterioration of the blend mechanical properties. They demonstrated that the use of SAN-GMA as a reactive compatibilizer copolymer, together with ethyltriphenyl phosphonium bromide (ETPB) as the catalyst, significantly reduced the interfacial tension between phases. Thus, ABS domain size, and consequently the impact strength and elongation at break were profoundly enhanced with minimum detrimental effects on tensile

324

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

strength and modulus. These enhancements were due to the reaction of the epoxide groups of SAN-GMA with PLA. Jo et al. [379] explored the effects of different types of compatibilizers on property enhancements of PLA/ABS blends for automotive applications. The tensile and impact strengths of blends were improved more effectively by the addition of GMA-g-SAN than either low Mw PC, PE-epoxy, MA-g-EPR, or MA-gSAN. Also, the incorporation of DCP further improved the mechanical properties of the blends, because of the in-situ produced ABS-g-PLA from the reaction between ABS and PLA [380]. A super tough PLLA/ ABS blend was also successfully prepared by adding reactive comb (RC) polymers as compatibilizers [381]. In other studies, two additives, one acrylic compatibilizer copolymer and one Joncryl ADR-4368C CE were used separately and together to increase the mechanical properties of PLA/ABS blends. The synergistic toughening effect of using both additives increased the impact strength by almost 600% [382–383]. It was also shown that the presence of ABS particles could enhance the crystallization of PLA through nucleation around ABS domains [384]. 4.5. PLA-PMMA Zhang et al. [385] explored the miscibility of PLA and poly(methyl methacrylate) PMMA through solution-precipitation and solutioncasting methods. From the first method, they achieved full miscibility, whereas the second method resulted in two separate phases. The miscibility of PLA and PMMA was also confirmed in another study [386]. The PLA ability to crystallize could also be restricted in the presence of PMMA molecules and almost no crystallinity could be observed in PLA blends with PMMA contents over 30 wt% [387]. Samuel et al. [388], using solvent-casting, found that PLLA/PMMA blends were immiscible with either a drop/matrix or co-continuous morphology, depending on the blend composition. However, after melt blending via a twinscrew extruder, miscible blends were obtained at any blend composition. Based on the miscibility feature, shape memory properties of PLLA/PMMA blends were also investigated, and the blends with same polymer contents appeared as the most efficient formulations for multiple-shape memory applications [389]. The same group also showed that the stereocomplex crystallization of PLLA/PDLA blends was also improved when PMMA was involved, due to the miscibility of PMMA with the PLLA and PDLA [390]. Similar results were reported by Bao et al. [391]. The rheological, thermomechanical, and mechanical properties of miscible blends of PLA/PMMA with different compositions were also extensively examined [392–393]. Anakabe et al. [394] studied the reactive extrusion of PLA/PMMA (80/20) blends by adding poly(styrene-co-GMA) copolymer. The copolymer improved the miscibility of the PMMA in PLA. The impact strength, elongation at break and thermal stability were improved, while the tensile strength and elastic modulus remained unchanged. Imre et al. [395] compared the properties of PLA/PS, PLA/PMMA, and PLA/PC blends. In all blends, the size of the dispersed particles differed significantly, indicating dissimilar interactions for the corresponding pairs. The blends containing the smallest dispersed particles exhibited the largest tensile strength, while PLA/PS blends with the coarsest structure had the lowest strength. It was shown that interfacial interaction was the strongest for the PLA/PMMA pair and weakest for PLA/PS. Imre et al. claimed that PLA/PMMA blends possess the superior combination of properties, an advantage for use in the automotive and electronic industries. 4.6. PLA-PET PET is an important commercial engineering thermoplastic with good thermal and mechanical properties, low permeability and chemical resistance. The thermal and mechanical characteristics of blends of PLA and PET were studied by Girija et al. [396]. The thermal stability of PLA was enhanced by the incorporation of PET, but if the addition of PLA to PET increased its stiffness it decreased the impact and tensile

strengths and the elongation at break of PET. The crystallization behavior of PLA/PET blends prepared through solution casting has also been extensively explored by Chen et al. [397]. The PLA/PET blends were found to be miscible through the whole composition range. The PET crystallinity decreased with increasing content of either amorphous or crystalline PLAs. However, the PLA crystallinity decreased only when PET was crystalline. The miscibility of PLA/PET blends was also confirmed over the entire blend composition range by Fu et al. and Huerta et al. [398–399]. Despite all these studies, Li et al. [400] illustrated that cold crystallized electrospun PLA/PET (70/30 and 50/50) blends were immiscible with two distinct glass transition temperatures. They confirmed that PET/PLA underwent phase separation in 70/30 and 50/50 blends during the electrospinning process, and during cold crystallization. In these immiscible blends, both PLA and PET crystallization were hindered. The immiscibility of PLA/PET blends containing a maximum of 20 wt% PLA was also shown by McLauchlin et al. [401] in injection molding experiments. The impact and tensile strengths of the blends were significantly reduced with the addition of PLA. Using singlescrew extrusion, partial miscibility of PLA/PET blends was reported for a maximum content of 7.5 wt% PLA [402]. Blends of 80 wt% PLA and 20 wt% of PET glycol-modified (PETG) with PLA-g-MA as a compatibilizer were analyzed by Jiang et al. [403]. They also reported immiscible, droplet-type morphology of the blends. Using rheological data and emulsion models such as the Palierne model, they showed that the use of 3 wt% PLA-g-MA significantly reduced the interfacial tension between PLA and PET. The droplet size was reduced and the size distribution was improved, causing significant enhancements of ductility without sacrificing the tensile strength and modulus. The rheological properties of PET from recycled bottles were negatively affected by the presence of PLA (up to 5 wt%) [404]. 4.7. PLA-PBT Poly(butylene terephthalate) (PBT) is a widely used polyester with high crystallization rate and high crystal melting temperature (higher than the PLA melting temperature). The PBT spherulites could, hence, behave as crystal nucleating agents for PLA. Blends of PLA and PBT are reported to be immiscible, although they have high compatibility due to interactions between their functional groups. This results in good dispersion and adhesion of phases [405]. Kim et al. [406] investigated the crystallization behavior of PLA/PBT prepared using paraphenylene diisocyanate (PPDI) as a chain extender via reactive extrusion. While PBT accelerated the PLA crystallization, PLA had a reverse effect on that of PBT. The crystallinity of both PLA and PBT phases was separately decreased by PPDI; however, when PLA, PBT and PPDI were all blended together, the crystallization rate of PLA was improved. The strong interfacial adhesion between PLA and PBT generated by PPDI lowered the degradation rate of PLA. Samthong et al. [407–408] also studied the effects of PBT droplet size and shape on the morphology and porous structure of the biaxially stretched PLA blend films. The stretched films composed of PBT droplets revealed ellipsoidal microvoids due to the interfacial debonding, and the void size corresponded to the PBT droplet size. They claimed that the PBT droplet size did not affect the void content of the stretched films. 4.8. PLA-PTT Poly(trimethylene terephthalate) (PTT) is an aromatic polyester, which is similar to PET and PBT, and when compared to PLA, it exhibits higher impact strength and better thermal stability. Lin et al. [409] reported that PLA/PTT, melt blended via a twin-screw extruder, were immiscible and as the PTT content increased, the thermal stability and elongation at break of PLA/PTT blends increased. This could expand the applications of PLA to films and molded objects. PTT crystallization rate was also accelerated in presence of PLA [409]. Analyzing their thermal and crystallization behavior, Zhou et al. [410–411] demonstrated

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

that PLA/PTT blends were miscible after melt blending using a singlescrew extruder. Melt spun fibers were processed using twin-screw extrusion and the resulting blends were determined as immiscible systems, with enhanced and hindered crystallization of PLA and PTT, respectively, in the presence of the other polymer [412]. The tensile strength of PLA was improved by the presence of PTT [412]. The immiscible blends of PLA/PTT were further studied in the presence of a random terpolymer as a reactive compatibilizer (i.e., EMA-GMA) [413] prepared via a twin-screw extruder. The tensile and impact strength were measured and predicted through modeling, and the tensile strength was shown to more sensitive to the terpolymer content, whereas the impact strength was significantly dependent on both terpolymer content and screw rotation speed. Droplet coalescence was minimized in the presence of the terpolymer, and the domain size was reduced while the interfacial adhesion was improved.

4.9. PLA-PC Polycarbonate (PC) has been widely used as an engineering thermoplastic with high thermal stability, impact resistance, and compatibility with aliphatic or aromatic polyesters. Therefore, when blending PLA with PC, the thermal stability and impact strength of PLA could be improved [414]. Immiscible blends of PC and PLA at a fixed ratio of 70/30 were prepared and the effects of three different compatibilizers, SANg-MA, poly(ethylene-co-octene) (EOR)-MA, and EGMA, were investigated [415]. The PLA domain sizes decreased significantly, decreased slightly, and increased, respectively, with these compatibilizers. Consequently, the incorporation of SAN-g-MA significantly improved the tensile, flexural, and impact strengths of the blends. From weighted relaxation spectra using the Palierne emulsion model, the interfacial tension between PLA and PC was seen to decrease from ~3.34 mN/m in the neat blend to ~0.08 mN/m in the blend with 5 phr SAN-g-MA. Wang et al. [416–417] showed that, in immiscible blends of PLA/PC (50/50), the use of an epoxy as a reactive compatibilizer during twinscrew extrusion significantly increased the HDT. The impact strength, however, was mainly improved using another compatibilizer, namely: PBSL. Reactive compatibilization of immiscible PLA/PC blends during extrusion was also investigated using tetrabutyleammonium tetraphenylborate (TBATPB) and triacetin. A new Tg indicated the formation of a PLA-PC copolymer after compatibilization, although the PC domain sizes unfavorably increased [418]. Reactive extrusion was also explored using epoxy-functional styrene acrylic copolymer, and the molecular weights of components was shown to increased and the compatibility between PLA and PC was improved with finer PC domain sizes and increased interfacial interactions. The blend HDT was also raised from 62 °C in (50/50) blends to ~106 °C after adding compatibilizer [419]. Lin et al. [420] used a random copolymer of styrene and GMA and N,N,N′,N′-tetraglycidyl-4,4′diaminodiphenyl methane (TGDDM) to improve the compatibility of PLA with PC, and thereby the thermal stability and impact strength of the blend by reducing the drop size and increasing the interfacial strength. Recently, Yuryev et al. [421] found that when blending branched PC with PLA rather than a linear PC, the impact strength and elongation at break could be further improved. The durability of PLA/PC blends, subjected to elevated temperatures and humidity conditions, was also shown to be enhanced [422]. On the other hand, Liu et al. [423] demonstrated that transesterification could occur between PLA and PC molecules, and the use of a catalyst could accelerate this reaction. Shear flow also promoted transesterification. The transesterification caused the reduction of PC domain sizes within PLA matrix. Yuriyev et al. [424] also investigated the mechanical properties in relation with hydrolytic degradation. The use of an acrylic impact modifier (EBA-GMA) significantly decreased the rate of moisture absorbance and, hence, the deterioration of properties.

325

4.10. PLA-PA PA has widely been used as an engineering thermoplastic due to its excellent combination of strength, stiffness, and toughness. Therefore, blending PLA with PA could improve the tensile and impact strengths as well as the elongation at break with respect to the neat PLA [425]. The first study on structure and properties of PLA/PA (PA6/PA66/ PA610 terpolymer) blends was probably conducted in 2010 by Feng et al. [426]. PLA and PA molecules can exhibit strong hydrogen bonding, which makes them partially miscible, as also confirmed by the Tg variation with blend composition. PA increased the crystal nucleation rate of PLA andwith the strong interfacial adhesion between PLA and PA the toughness and ductility of the blend are improved compared to the neat PLA. Wang et al. [427] also blended polyethylene-octene elastomer grafted maleic anhydride (POE-g-MA) with PLA/PA6 to improve the impact strength and elongation at break of the blend. POE-g-MA was an effective compatibilizer as it reduced the PLA domain sizes and improved its uniformity and compatibility with the PA6 matrix. Blends of PLA with PA6 were further studied by Sedlarik et al., Kucharczyk et al., and Khankrua et al. [425,428–430]. The use of compatibilizers, alkenylsuccinide-anhydride-amide (ASAA) and alkenyl-succinic anhydrideimide (ASAI), reduced the domain size of the dispersed phase and significantly enhanced the impact and tensile strengths [429]. Khanukra et al. [430] demonstrated that the use of 5.0 phr of two different chain extenders (multifunctional epoxide, ECE and polycarbodiimide, PCD) in PLA/PA6 (70/30) blends increased the tensile modulus and strength, impact strength and elongation at break of the blend although the droplet morphology did not vary with the addition of chain extenders. 4.11. PLA-PEG, PEO, or POE PEG is a hydrophilic polyether compound being used in areas from industrial manufacturing to medicine. Other chemically synonymous molecules of PEG are also known as PEO and POE. The Tg and Tm are reported as ~−54 and 74 °C, respectively [431]. Generally, PEG, as an oligomer or a polymer with a molecular weight (Mw) below 20,000 g/mol, is preferred in the biomedical field. PEO also refers to polymers with a Mw beyond 20,000 g/mol and is mostly used as chemical additives. POE also refers to polymers of any Mw [432]. Younes et al. [433] studied the morphology of PEG/PLA blends comprising PEG chains of different Mw values (1500, 3400, 6000 and 35,000) although no conclusive evidence was given for their miscibility. Nijenhuis et al. [431] extensively explored degradation characteristics, mechanical properties and thermal behavior of PLA/PEO blends. They found that high Mw PEO and PLLA were miscible in the molten state as a single Tg was observed. As the PEO concentration increased, the crystallization rate of PLA and the blend elongation at break increased, whereas the tensile strength decreased. The hydrolytic degradation rate of PLA in blends was also faster than for the neat PLA. Similar results were reported by other authors [434–435]. Sheth et al. [436] also studied the properties of PLA/PEG blends. They claimed, however, that PLA/PEG blends ranged from being miscible to partially miscible, depending on the concentration. Below 50 wt% PEG, higher elongation at break and lower modulus were obtained, whereas beyond 50% the increased crystallinity caused an increase in modulus and a decrease in elongation at break. In all scenarios, the tensile strength decreased linearly with PEG content. Enzymatic degradation was also faster in blends than in the neat PLA. Hu et al. [437–438] investigated the properties of PLA/PEG blends and confirmed that for blends up to 30 wt% and 20 wt% PEG were miscible in amorphous and semicrystalline PLAs, respectively. The addition of 30 wt% PEG to amorphous and semicrystalline PLAs increased the elongation at break to 500 and 300%, respectively, and decreased the modulus to 5 and 20 MPa, respectively, when no aging occurred. The PLA/PEG 70/30 blends, however, became increasingly rigid over time at ambient conditions for high D-content PLA, due to gradual crystallization of PEG. The formed PEG crystallites raised the Tg and hence the modulus and

326

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

strength but reduced the elongation at break. In low D-content PLA, blends with 30 wt% PEG could be quenched from the melt to a uniform miscible amorphous phase. However, after leaving at ambient temperature, the phase-separation occurred at this composition due to the crystallization (aging) which increased the rigidity and reduced the elongation at break from 300 to 150%. Lai et al. [439] also reported that PLA and PEG were miscible in the melt. The crystallization of PLA was accelerated due to the plasticization role of PEG; however, PEG crystallization was retarded due to the increased rigidity of the system originating from the PLA crystallization. The use of compatibilizers or chain extenders in PLA/PEG blends has also been explored. PLA/PEG blends containing PLA-g-MA to increase the miscibility of PLA with PEG were prepared via reactive extrusion, but the thermomechanical properties were not much affected [440]. Gui et al. [441] showed that when blending PLA with PEG-co-citric acid (PEGCA) not only the elongation at break but also the toughness and impact strength increased significantly. Via reactive mixing, PLA was also blended with acrylated-PEG. While the blends were miscible, the elongation at break was increased by only 18% compared to the neat PLA while the modulus was reduced to 0.4 GPa [442]. Park et al. [443] showed that blend elongation at break increased up to 390% with respect to the neat PLA when blending 20 wt% PEG with PLA, whereas the tensile strength and modulus were reduced to 16 and 420 MPa, respectively. The elongation at break, tensile strength and modulus changed to 540%, 38 and 880 MPa, respectively, when blending 20 wt% of a branched PEG with PLA. The dynamic moduli and complex viscosity of PLA/PEG blends were also shown to drastically decrease with PEG content [435,444]. Using gas antisolvent techniques, Elvassore et al. [445] produced insulin and insulin/PEG-loaded PLA nanoparticles. For drug delivery purposes, studies were carried out on core-shell structures of PLA-PEG nanoparticles [446]. Three-dimensional PLA/PEG hydrogel structures were also produced for the first time with a narrow pore size distributions and excellent pore interconnectivity. These structures exhibited good cell seeding characteristics and proliferation [447]. Attempts were made to produce nanofibers of PLA/PEO through solution blow spinning for making drug-loaded fiber-mats [448]. Three-D (3D)printed scaffolds were also recently produced by Serra et al. [449] using PLA/PEG blends. They showed that the use of PEG not only eased PLA processing, but also enhanced the degradation rate of scaffolds.

4.12. PLA-POM Poly(oxymethylene) (POM) has a similar molecular chain structure as PEO, but POM consists of methylene groups rather than ethylene groups in PEO. The miscibility and phase diagram of PLA/POM blends was investigated by Qui et al. [450]. They showed the synergistic effect of PLA and POM on toughness improvements. PLLA/POM blends exhibited much higher elongation at break than PLLA or POM alone, with excellent tensile strength and modulus. This may be due to the double T g depression and improved mobility of PLA and POM. Qui et al. also showed that PLA crystallization was enhanced significantly with POM content, while the blend possessed excellent optical transmittance [451]. PLA/POM blends were also prepared using injection molding [452]. With increased injection speed, the POM dispersed phase became more uniformly distributed and, hence, the mechanical properties were improved. Guo et al. [453] obtained immiscible blends of PLA/POM with a unique stacked layered structure. This structure caused increases of HDT, modulus, and elongation at break with POM content. Consequently, it was considered that POM was a new efficient eco-friendly polymer for enhancing the thermo-mechanical properties and processability of PLA, which might expand the applications of PLA [451].

4.13. PLA-PVPh Poly(vinylphenol) or PVPh is a thermoplastic structurally similar to polystyrene and is mostly used in electronic applications. Zhang et al. [454–455] studied the miscibility of PLA and PVPh and, via DSC, demonstrated that PLA/PVPh blends were partially miscible. Using Fourier transfer infrared (FTIR) analysis, weak hydrogen-bonding interactions were observed between the carbonyl groups of PLA and the hydroxyl groups of PVPh. They also showed that when the PVPh content increased beyond 40 wt%, crystallization of PLA was hindered significantly. Meaurio et al. [456–457] illustrated that the PLA/PVPh blends were miscible for the blends obtained by solution casting, except for PVPh-rich blends. They confirmed that the negative value of the interaction parameter confirmed a thermodynamically miscible state of this blend. Using molecular dynamics simulations, the miscibility of PLA and PVPh was also analyzed and compared with that between PLA and PS [458] via calculations of the Flory-Huggins interaction parameter. The miscibility was confirmed for PLA and PVPh, while complete immiscibility of PLA and PS was also demonstrated. 5. PLA binary blends with elastomeric polymers 5.1. PLA-rubber Attempts have been made to modify the impact properties and ductility of PLA by blending it with biodegradable rubbers. The first attempts started in 1991 when the group of Pennings [18–20] claimed the achievement of super-tough biodegradable PLA products for biomedical applications with a critical poly(L-lactide-co-caprolactone) rubber content of 20 wt%. Semi-crystalline PLAs could have improved impact properties to a greater extent (i.e., 420 J/m) than amorphous non-crystallizable matrices (i.e., 405 J/m). However, the strain at break improvement was more significant for blends based on amorphous PLAs (~130%) than those based on semi-crystalline PLAs (~11%). Besides this effort, Pennings et al. also investigated how the PLA toughness and ductility could be improved by block copolymerization with PCL as a biodegradable rubber. The first serious attempts to toughen PLA using different types of synthetic rubbers started when Ishida et al. [459] investigated the toughening of PLA by melt blending it with four different types of rubber. The major issue about the blends of PLA with synthetic and natural rubbers is known to be the incompatibility and full immiscibility between the two polymers, which could result in poor final properties. Ishida et al. reported that when using different types of rubber, the differences in surface energy values influenced the interfacial adhesion between rubber droplets and the PLA matrix, and thereby the rubber domain size/distribution within PLA. Therefore, the toughening efficiency might significantly vary for each PLA-rubber blend, and even in some cases the properties could be worse than of the neat PLA. Among ethylene–propylene rubber (EPM), ethylene–acrylic rubber (AEM), acrylonitrile–butadiene rubber (NBR), and isoprene rubber (IR), NBR exhibited the lowest interfacial tension with PLA, the most homogeneous and finest dispersion, and consequently the highest impact strength (even if only 2 times higher than PLA). In the sections below, the studies on PLA blends with different types of rubber are examined and compared. The majority of these studies focused on the use of natural rubber (NR), while a few studies have also been conducted on blends with poly(styrene-butadiene-styrene) (SBS), poly(styrene-ethylene-butylene-styrene) (SEBS), and some other different elastomers. 5.1.1. PLA-NR (natural rubber) Intensive studies on the development of immiscible PLA/NR blends started only a few years ago. The effects of melt processing parameters and NR content on the morphology, mechanical and rheological properties, and crystallization behavior of PLA/NR blends were thoroughly studied by Bitinis et al. [460]. At NR loading of 10 wt%, where the NR

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

droplets size was around 1 μm, the PLA ductility increased up to 200% and significant improvements of the melt strength and crystallization of PLA were reported. PLA/NR (90/10) blends with and without 1 wt% crystal nucleating agent were also prepared using an internal mixer [461]. Regardless of their effects on the PLA crystallinity, the nucleating agents showed only small improvements of mechanical properties of the PLA/NR blends, indicating the dominant role of NR on controlling the blend mechanical properties. Juntuek et al. [462] observed that with increasing NR content up to 10 wt%, the impact strength and elongation at break of PLA/NR blends increased up to 40 kJ/m2 and 75%, respectively. They also showed that using 1 wt% GMA-g-NR as a compatibilizer significantly improved the impact strength and elongation at break of PLA/NR (90/10) blends to ~52 kJ/m2 and 160%, respectively, while maintaining the tensile strength and modulus. Two poly (1,4-cis-isoprene)s, derived from natural and synthetic rubbers, were also blended with PLA and the fracture mechanism was compared Kowalczyk et al. [463]. Incorporation of 5 wt% rubber showed the highest toughening efficiency (from 58 kJ/m2 in the neat PLA up to ~105 kJ/m2 in the blend). The toughening mechanism was considered to be associated with crazing initiated by the rubber particles followed by cavitation inside rubber particles, which further promoted shear yielding of the PLA. Kowalczyk et al. showed that the strain at break remained unaffected. The effect of NR-g-PVAc as a compatibilizer on PLA/NR blends was also explored by Chumeka et al. [464]. NR-g-PVAc increased the miscibility of PLA and NR and reduced the NR droplet sizes down to submicron level. The strain at break increased by up to 30% while the impact properties were not affected significantly. To enhance the compatibility of NR with PLA, Huang et al. [465] showed that the addition of DCP as a compatibilizer increased the impact strength of PLA/NR blends from ~4.5 to 7.5 kJ/m2; however, it did not influence considerably the strain at break of the blends. Moreover, due to its cross-linking effect, the addition of DCP improved the processing (rheological) properties of the blends. The use of a triblock copolymer of PLA-NR-PLA synthesized as a compatibilizer further improved the impact strength (up to ~12 kJ/m2) and elongation at break (up to ~10%) of the PLA/NR blends [466]. The structure and properties of PLA/NR with and without two different compatibilizers (PLA-g-MA or NR-g-MA) also showed that the Tg of PLA decreased due to the increased compatibility between PLA and NR; however, elongation at break and impact strength were not improved considerably [467]. Using 0.5 wt% sorbitan ester (SE) as a compatibilizer, it was found that the impact strength of PLA/NR blends increased up to 380 J/m [468]. Bijarimi et al. [469] studied the properties of immiscible blends of PLA/ epoxidized-NR (ENR) with and without liquid natural rubber (LNR) as a compatibilizer. The addition of 5 wt% LNR simultaneously improved

327

the blend tensile strength and elongation at break (to ~300%). LNR reduced the interfacial tension between the two phases and, hence, improved the NR domain size uniformity. Bijarimi et al. also showed that the use of liquid-ENR (LENR) as a compatibilizer could improve the compatibility between NR and PLA and hence improve the final blend properties [470]. The addition of LNR as a compatibilizer was also shown to increase the impact and tensile strengths due to enhanced interfacial adhesion and reduced droplet sizes [471]. The behavior of rubber toughened PLA with either NR, ENR, or NR-gPMMA was also compared by Jaratrotkamjorn et al. [472]. Among all, NR revealed to be the best toughening agent. The addition of 3 phr of ENR to PLA/NR (85/15) blends was also shown to compatibilize the two phases [473]. Zhang et al. [474] confirmed that ENR and PLA were compatible, and the impact strength and strain at break increased compared to the neat PLA by 4 and 3 times, respectively. Desa et al. [475] prepared PLA/NR blends in presence of 5 wt% carbon nanotubes, which were localized in the NR phase. Slight improvements in the impact strength and elongation at break of PLA/NR/CNT were observed at 20 wt% NR content. Recently, the toughening behavior of PLA was further explored by adding NBR via melt mixing while the authors investigated the influence of the acrylonitrile content on the compatibility, microstructure, tensile properties and impact resistance of the PLA/NBR blends [476]. The rubber particle size and the interfacial tension increased with increasing acrylonitrile and NBR contents. Accordingly, the incorporation of only 10 wt% NBR with a minimum 20 wt% of acrylonitrile content increased the elongation at break and impact strength to around 110% and 150 J/m, respectively [476]. The group of Chen [477–478] produced a super-toughened PLA/NR blend prepared via a dynamic vulcanizing technique, where NR had a continuous network-like dispersion. Their blend exhibited superior properties compared to those of conventional PLA/NR blends with drop-type structures. Chen et al. showed that the impact strength increased up to 500 J/m in PLA/NR (65/35) blends [479]. They further examined the PLA/ENR blend behavior when processed via peroxideinduced dynamic vulcanization. Similar continuous network-like structures embedded in the PLA phase with superior properties were successfully generated [480]. It was confirmed that a remarkable brittle −ductile transition (with strain at break up to ~250%) occurred at ENR content of 40 wt% and the blend impact strength was 47 kJ/m2, nearly 15 times than that of the neat PLA [481]. The same group [482] further examined the properties of PLA/NR blends prepared through phenolic resin-induced dynamic vulcanization. Similar cross-linked continuous NR phase structure in PLA was generated. The viscoelasticity of the PLA melt was also largely improved by the cross-linked NR phase; however, the crystallization of PLA was retarded. Fig. 10, shows the

Fig. 10. SEM images of the NR network-like dispersion in a dynamically vulcanized PLA/NR (65/35) blend (etched surface) (a) and its fracture surface (b). Images are taken from [475].

328

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

Fig. 11. (a) Elongation at break, (b) tensile strength, and (c) impact strength of various PLA/NR blends. Data adapted from different studies.

microstructure of this novel generated continuous rubber network in the dynamically vulcanized PLA/NR (65/35) blends. Fig. 11 also summarizes the best achievements in impact strength, strain at break and the corresponding tensile strength in various studies on PLA/NR blend systems.

5.1.2. PLA-SBS The incorporation of SBS copolymer as a blending component with PLA has been studied by a few researchers. Zhang et al. [483,486] showed that PLA and SBS were immiscible although the reduced Tg of PLA indicated compatibility of the phases. The elongation at break and tensile strength of PLA were, respectively, increased and reduced, which later on was also confirmed by Wu et al. [484] and Wang et al. [485], although the latest study was conducted on blends of PLA and epoxidized-SBS (ESBS). Zhang et al. and Wu et al. showed that the elongation at break in PLA/SBS (70/30) blends did not exceed 20%. Wang et al. also reported that the elongation at break of PLA/ESBS (70/30) blends was dramatically larger (~254%) than that of PLA/SBS (70/30) blends (23%). Moreover, the impact strength was also drastically larger, with a value of 890 J/m (~30 times).

5.1.3. PLA-SEBS Research on immiscible blends of PLA and SEBS copolymer also started very recently [486–487]. It has been shown that with 30 wt% SEBS, the elongation at break of PLA/SEBS blends did not exceed 10% [486]. Sangeetha et al. [487] used MA-g-SEBS to make the blend phases more compatible and showed improvements of the impact strength, whereas the tensile and flexural strengths were reduced and the elongation at break slightly lowered.

5.1.4. PLA-other rubber elastomers Jiang et al. [488] investigated the blends of PLA with various elastomers, i.e., EGMA, MA-g-SEBS, and EOR. EGMA was found to be highly compatible with PLA, whereas MA-g-SEBS was less compatible, and EOR was completely incompatible. Therefore, PLA/EGMA blends showed a finer morphology that led to a significant improvement of the impact strength to ~88 kJ/m2 in blends containing 40 wt% elastomer, which was 20 times larger than that of the neat PLA. These values were around 45 and 15 kJ/m2 in PLA blends with MA-g-SEBS and EOR, respectively. Zhao et al. [489] utilized ultrafine fully-vulcanized powdered ethyl acrylate rubber (EA-UFPR) as a PLA toughening modifier. They showed that the addition of 1 wt% EA-UFPR was sufficient to supertoughen the PLA with elongation at break of 225%, while maintaining the tensile strength. The high compatibility between PLA and EA-UFPR particles generated strong interfacial interactions. Liquid polybutadiene rubber (LPB) was blended with PLA, through reactive blending using DCP [490]. Due to the significant increase in the PLA-LPB compatibility, the LPB domains were reduced, which enhanced the toughness and melt strength of PLA. The strain at break improved from ~10% in the non-reacted PLA/LPB to ~40% in reactively modified PLA/LPB without tensile strength sacrifice. PLA was also toughened by adding 12 wt% of various thermoplastic elastomers including poly(ether-b-ester) (PEEs), poly(ether-bamide) (PEBA) and poly(ether-b-urethane) (PEU) [491]. It was shown that the strain at break and impact strength improved with the addition of the noted elastomers; however, PEBA appeared to be the most efficient. Reactive compatibilisation with 2 wt% of 4,4-methylene diphenyl diisocyanate was also conducted and all compatibilised blends revealed high toughness, but similar ductility values while preserving sufficient stiffness and strength [491]. Similarly, compatibilized PLA/PEBA blends were found to behave as a supertough PLA system [491]. In another recent investigation of in Macosko's group

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

329

[492] PLA was toughend by blending with b10 wt% of PEO-PPO-PEO (EPE) triblock copolymers and it was showed that EPE copolymers with long PPO block and low PEO fraction were more efficient in toughening PLA although they were less miscible with PLA. The authors claimed that the toughening mechanism was similar to the rubber toughening of brittle plastics [492].

[498]. The PUEP reacted with PLA during melt-blending, and resulted in an improved interfacial compatibilization. The effective in-situ reactive interfacial compatibilization and dynamic vulcanization significantly increased the impact strength up to around 55 kJ/m2 (~20 times more than that of the neat PLA) and strain at break up to 500%, with moderate strength and stiffness.

5.2. PLA-PU

5.2.2. PLA-thermoplastic PU Thermoplastic PU (TPU) elastomers have a unique combination of toughness, durability, flexibility, biocompatibility, and biostability. TPUs are linear segmented block copolymers of alternating soft and hard segments. At operating temperatures, thermodynamic immiscibility of soft and hard segments results in phase separation and, consequently, in the formation of a micro-domain structure of hard segments. Soft segments are either polyester or polyether, which are expected to have good compatibility with PLA, as PLA has been shown to be miscible in some polyesters and polyethers. Li et al. [499] showed that PLA and TPU were partially miscible, but exhibiting a two-phase morphology. The ductility and impact strength of the blends were significantly increased with increasing TPU content, due to the strong interfacial adhesion, which led to a shear yielding toughening mechanism. On the other hand, the tensile strength and modulus decreased with TPU content. Very similar results were also reported by other authors [500–504]. Hong et al. [503] later showed that PLA/TPU blends exhibited a shear-thinning behavior. Li et al. [499] found that TPU accelerated PLA crystallization, although it reduced the final crystallinity content. Fig. 12 summarizes the mechanical properties of PLA/TPU blends with data adapted from different studies. As depicted, the property variation trends are quite similar in most of studies where no compatibilizers have been utilized. Reactive compatibilization of PLA/TPU blends with 1,4 phenylene diisocyanate (PDI) was also conducted due to the potential interactions of diisocyanates with -OH/-COOH groups during reactive processing of PLA/TPU blends in melt processing [505]. The PDI increased the phase

5.2.1. PLA-thermoset PU Yuan et al. [493] studied the toughening effect of a small amount of interpenetrating polyurethane (PU) thermoset resin on PLA with various degrees of cross-linking. Maximum toughness of 18 MJ/m3, which was an order of magnitude larger than that of the neat PLA, was achieved by introducing 5 wt% of an adequately cross-linked PU network. The toughness was smaller when the PU was either linear or overly cross-linked. Zeng et al. [494] and Feng et al. [495], respectively, investigated the blending behavior of PLA with poly(ester-urethane), which contained PBS as a flexible segment, and poly(ether urethane) based on PEG blocks via a chain-extension reaction by diisocyanate. In both studies, the elongation at break was improved to ~320 and 300%, respectively, whereas the tensile strength and modulus were reduced. Zeng et al. also showed that the increase in poly(ester-urethane) content enhanced the crystallization rate. PLA/PU blends were also prepared by reactive processing by Imre et al. [496] who successfully obtained a coupling of the phases and enhancement of interfacial interactions with reduced dispersed phase sizes to b0.5 μm. The coupling was achieved through the isocyanate groups reacting with the hydroxyl and carboxyl end-groups of PLA, which resulted in the formation of PLAb-PU copolymer acting as a compatibilizer. Liu et al. [497] successfully toughened PLA with PU in-situ cross-linked during reactive blending, which significantly improved the PLA-PU interfacial compatibility and hence the strain at break and impact strength up to 250% and 550 J/m, respectively. Super-toughened PLA/PU-elastomer-prepolymer (PUEP) blends were successfully prepared by a dynamic vulcanizing technique

Fig. 12. (a) Elongation at break, (b) impact strength, (c) tensile strength and (d) tensile modulus of the PLA/TPU blends, (data adapted from different studies).

330

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

compatibility, reduced the TPU domain sizes and improved the melt strength and elongation at break up to 400%. In another study, 3aminopropyl triethoxysilane (APTES) was used as a reactive compatibilizer [506]. This study also showed that the addition of the compatibilizer improved the compatibility between TPU and PLA, which led to the decrease of TPU domain sizes and a better dispersion within the PLA matrix. Low contents of APTES improved the impact strength further, from 29.2 to 40.7 J/m, but with a limited improvement in the tensile properties. Due to the increased interaction between PLA and TPU, the blend viscosity also increased with small content of APTES. However, with further increases in APTES content the viscosity was reduced due to the dominant role of the plasticization effect. To increase the phase miscibility, Zhao et al. [507] used MDI as compatibilizer through reactive melt blending. They showed that the MDI addition did not improve the phase compatibility much, but it rather reacted with TPU phase and extended the TPU chains, which formed a branched and cross-linked structure. The impact strength and elongation at break improved up to ~100 kJ/m2 and 390%, respectively, until an optimum MDI content (i.e., 0.8 wt%), whereas the tensile strength continuously increased with the MDI content. Oliaei et al. [508] illustrated that without the use of a compatibilizer and only by utilizing ester-based TPU, a successful compatibilization between PLA and TPU occurred, which could lead to enhancements in morphology, thermal, mechanical and rheological properties of the blend systems. TPU was also melt-blended with PLA to improve the shape memory effect of PLA and the shape recovery of the blends under various conditions and blending ratios was investigated [509–510]. The biodegradation of PLA/TPU blends was also studied [511] and it was shown that co-continuous blends revealed larger initial degradation rates than blends with droplet-like morphologies. 5.3. PLA-EVA and EVM There are three different types of ethylene-vinyl acetate (EVA) also known as poly(ethylene-co-vinyl acetate) (PEVA), which differ in the

vinyl acetate (VA) content and their applications. The EVA copolymer with low VA content (~ up to 4%) may be referred to as vinyl acetate modified PE that is processed as a thermoplastic similar to LDPE. When the VA content is moderate (~4 to 30%), the copolymer is referred to as thermoplastic ethylene-vinyl acetate copolymer (EVA) and behaves as a thermoplastic elastomer. The copolymer with VA contents higher than 40% is referred to as ethylene-vinyl acetate rubber (EVM) [512]. Blends of PLA and EVM, as microspheres, were first prepared by Burt et al. [513] in 1995 for controlled drug delivery systems. Electrospun PLA/EVM blends were also explored [514] for their usage in drug delivery applications. Gajria et al. [295] suggested that blends of PLA and polyvinyl acetate (PVA) are miscible, and, subsequently, Yoon et al. [515] demonstrated that EVM containing 85 wt% of VA was miscible with PLA. However, with the decrease in VA content to 70 wt %, the blend became immiscible. In other words, the increase in ethylene content of EVA increased the immiscibility of PLA and EVM. The tensile strength and modulus of t PLA-EVA blends with VA content of 85% (EVA85) blends were reduced, accompanied by an increase in strain at break. Research on PLA/EVA blends was limited until 2010; however, since 2011 several investigators started to focus on the development of these blends. Liu et al. [516] studied the drug delivery behavior of PLA/EVA blends. The properties of PLA/EVA and PLA/EVM were extensively explored by Ma et al. [517] using EVA with varying VA concentrations. As also noted earlier, the miscibility, compatibility and phase morphology of the PLA/EVA blends were controlled by the VA content in EVA. Fig. 13 presents TEM images of PLA/EVA (80/20) blends with VA contents of 0, 40, 50, 70, and 90 wt%. The EVA droplets became more homogenous and finer with increasing VA content. However, the impact strength and elongation at break were maximized in blends with EVA of VA content of 50 wt%. The impact strength and elongation at break were increased from 3 kJ/m2 and 9%, respectively, for the neat PLA, to around 64 kJ/m2 and 340%, respectively, for PLA/EVA (80/20) blends with EVA containing 50 wt% VA. Morphological and mechanical properties of the PLA/EVA50 blends (50 wt% VA) were also explored as a function

Fig. 13. TEM images of PLA/EVA (80/20) blends with various VA contents in EVA: (a) 0 wt%, (b) 40 wt%, (c) 50 wt%, (d) 70 wt%, and (e) 90 wt% (adapted from [517]).

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

331

Fig. 14. TEM images of the PLA/EVA blends (EVA of VA content of 50 wt%) with various EVA contents of (a) 5 wt%, (b) 10 wt%, (c) 15 wt%, (d) 20 wt%, and (e) 30 wt% (adapted from [517]).

of the EVA content. Fig. 14 shows the TEM images of PLA/EVA blends (EVA of VA content of 50 wt%) with EVA contents of 5, 10, 15, 20, and 30 wt%. With increasing EVA content, the EVA droplet sizes increased, and the impact strength and elongation at break raised up to ~83 kJ/m2 and 400%, respectively. The toughening mechanisms were explained to be associated with cavitation inside the rubber particles in combination with a matrix yielding. PLA/EVM blends were also prepared via dynamic cross-linking (vulcanization) using DCP [518]. The authors showed that the cross-linking efficiency was for DCP contents b1 wt%. This resulted in blends not only with high strain at break, but also high tensile strength. They also reported that in films of PLA/EVM blends, a high transparency was retained in presence of EVM [519]. Super-toughened PLA/EVA blends with moderate strength and stiffness were also prepared via peroxideinduced dynamic vulcanization and interfacial compatibilization [520]. A maximum of 110% strain at break and 90 kJ/m2 impact strength were obtained. Improved toughness and ductility of PLA through blending with EVA have also been reported by Singla et al. [521]; however, the tensile strength and modulus were reduced. They also claimed that the incorporation of EVA hindered the PLA crystallization, although Pracella et al. [522] showed that the crystal growth rate of PLA increased with EVA content in their miscible blends. Xinyan Shi and co-workers extensively explored the damping properties of PLA/EVM blends by examining the effects of added polyol, fillers, and heat treatment using dynamic mechanical analysis (DMA) experiments [523–526]. The branched polyol behaved as a compatibilizer in the blends and significantly improved the damping properties of blends [524]. When heat treated, the damping properties deteriorated as EVA continued to cross-link and the PLA tended to further crystallize, although increases in the polyol content hindered the PLA crystallization [523]. The addition of acrylic rubber (ACM) or polyvinyl chloride (PVC) also improved the damping properties of blends due to their compatibility with EVA [525]. Further, blends filled with

mesoporous silica and glass beads showed improved damping performances [526]. The enzymatic degradation of blends of EVA (with 18 wt% VA content) with PLA was studied by Cong et al. [527] who showed that the increase of EVA to 40 wt% raised the degradation rate of PLA. Using titanium propoxide (Ti(OPr)4) as a catalyst, EVA/PLA blends compatibilized with EVA-g-PLA copolymers were synthesized by reactive extrusion, via the transesterification reaction between EVA and PLA. The samples were then characterized following exposure to different environments [528]. UV radiation induced structural modifications, and hence influenced rheological and mechanical properties. Blends with larger amounts of EVA-g-PLA had lower photo durability and faster biodegradability, which is promising for applications with short lifetime objects, like packaging. 6. PLA binary blends with other polymers The miscibility of PLA and polyhydroxy ester ether (PHEE) blends was studied by Cao et al. [529]. Initial DSC thermograms showed that PLA and PHEE were immiscible. After repeated heating–cooling cycles, PLA and PHEE tended to behave as a miscible phase and eventually exhibited a single Tg. This means that although the blend components were miscible, the initial blend mixing/processing was inadequate. Under the repeating cycles molecular mixing and solubility were reached. Poly(vinylpyrrolidone) (PVP) is an environmentally friendly synthetic polymer that has been widely used in biomedical, biochemical, food, and textile areas because of its nontoxic and water-soluble properties. Zhang et al. [530] showed that although PVP was immiscible with PLA it was compatible with PLA as the Tg values were closer to each other. PVP also restricted PLA crystallization. Blends of PLA with poly(viny1 butyral) (PVB) were investigated using a solution casting method [531]. The absence of variations of Tg of the phases indicated that PLA and PVB were immiscible. The

332

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

crystallinity of the PLA phase remained also constant with increasing PVB content in the blends. Blends of PLA and poly-p-dioxanone (PPD) were studied at different compositions [532]. According to DSC results, the blends were completely immiscible. The blend containing 20 wt% PPD was more ductile and tougher as PPD might act as a plasticizer. Blends of PLA and poly(butyl acrylate) (PBA) were shown to exhibit partial miscibility [533]. With 15 wt% PBA the strain at break and tensile toughness of the blends increased considerably, up to ~175% and 47 MJ/m3 from ~4% and 2 MJ/m3 for the neat PLA, respectively. Also, the addition of PBA significantly accelerated the PLA crystallization rate. PLA toughening was further explored by blending it with a novel bioelastomer (BE), synthesized from biomass-based diols and diacids [534]. When the BE content was 11 vol%, the elongation at break increased from 7% in the neat PLA to ~180%, and the impact strength increased from ~2.4 to ~10.3 kJ/m2. SEM images indicated that the toughening mechanism was largely due to the matrix deformation, which was induced by the cavitation of rubber particles. PLA was also toughened by blending with a novel biodegradable aliphatic–aromatic copolyester - random poly(butylene succinate-coglutarate-co-adipate-co-terephthalate) (PBSGAT) [535]. Immiscible blends with 25–35 wt% PBSGAT showed a 20-times increase in the strain at break and 250% increase in the tensile impact strength. It was suggested that the main mechanism of the toughening was shear yielding and further plastic deformation of the PLA matrix, originating from the cavitation of the copolyester droplets. Blends of PLA and thermoplastic polyolefin elastomer (TPO) were studied while using TPO-g-PLA as a compatibilizer [536]. TPO droplet sizes were significantly reduced with TPO-g-PLA due to the increased interfacial compatibility. Accordingly, the elongation at break, toughness, and impact strength were considerably improved. It was claimed that a super-tough PLA can be produced via blending with EGMA [537]. The PLA/EGMA (80/20) blend exhibited an elongation at break beyond 200%, although the impact strength was not very high (b10 kJ/m2). However, when the blend was annealed, the impact strength increased to ~70 kJ/m2 although the strain at break was reduced to ~12%. It was claimed that the induced crystallization of the PLA matrix after annealing played an important role in the toughening although the ductility was decreased. Li et al. [538] studied the blending properties of PLA and poly(ethylene-co-octene) (PEOc) while using EGMA as a compatibilizer. PLA and PEOc were shown to be immiscible, but the PEO droplet sizes were significantly smaller with the addition of EGMA up to 2 wt%. Further additions of EGMA produced no extra enhancement. EGMA significantly increased the complex viscosity and storage modulus of the blends at low frequencies, due to enhanced compatibility. The elongation at break and impact strength were reported to be ~107% and 8 kJ/m2, respectively. In another study [539], the blend behavior of PLA and GMA-g-PEOc was analyzed. Without grafting, PLA-PEOc with 15 wt% PEOc showed improvements in elongation at break (from 21% in PLA to 67%) and impact strength (from 4 kJ/m2 to ~20 kJ/m2). However, these values were dramatically increased in the PLA/GMA-g-PEOc blends (with a similar blending ratio) to ~133% and 30 kJ/m2, respectively. This was due to the increased compatibility and reduced droplet sizes. Super-tough blends of PLA and PA elastomers (PAE) were also examined in the work of Zhang et al. [324]. They showed that in partially miscible blends of PLA/PAE with 30 wt% PAE, the elongation at break drastically increased to 367%, through which unique shape memory behavior was also exhibited. Liu et al. [540] claimed that PLA/PAE blends are immiscible with weak interfacial interaction between the two phases. The properties of PLA and poly(ethylene glycol-co-propylene glycol) (PEPG) were also explored by Ran et al. [541]. The PEPG behaved as a macromolecular plasticizer, which could improve the flexibility of the neat PLA. PEPG was miscible with PLA in the blend composition range

of 5 to 20 wt%. It was shown that in PLA/PEPG (80/20) blends, with a fully amorphous PLA, the elongation at break increased up to 550% while the tensile strength was reduced to almost half of that of the neat PLA. When using a crystalline PLA or annealing the blends, phase separation occurred due to PLA crystallization and the flexibility and elongation at break decreased significantly. A PLA-b-poly(dimethyl siloxane) (PDMS) block copolymer was added as a compatibilizer to blends of PLA and PDMS [542]. The PLAb-PDMS was obtained via transesterification. The blends of PLA/PDMS containing PLA-b-PDMS exhibited a highly improved elongation at break of ~140%. PLA/ethylene-glycidyl methacrylate-vinyl acetate (EGVA) (30/ 70) blends with a partial dual-continuous network-like structure and shape memory properties were studied by Xu et al. [543]. Methylhexahydrophthalic anhydride (MHHPAintroduced selective cross-linking (vulcanization) in the blends. Dynamic vulcanization caused the morphology to evolve from a drop-type to a partial dual-continuous network-like morphology. Consequently, the PLA/ EGVA blends exhibited excellent shape memory properties due to the strong resilience of the selectively cross-linked EGVA phase. The selective cross-linking increased the complex viscosity, elasticity, and the solid-like behavior of the PLA/EGVA blends. Meanwhile, the high elongation at break (250%) was tunable by tailoring the cross-link density and phase morphology. The crystallization of PLA was enhanced by blending it with polyvinylidene fluoride (PVDF) [544,444]. The cold and melt crystallization of PLA was accelerated after blending with PVDF. The earlier crystallization of PVDF in the PLA matrix generated crystal nucleating sites for PLA around the nucleated crystals of PVDF. The PLA crystal growth on PVDF crystallite domains generated a trans-crystalline structure at the PLA/PVDF interface. The enhancement of PLA crystallization by the incorporation of PVDF as a minor dispersed phase was also confirmed by Salehiyan et al. [545]. Using reactive comb (RC) polymers (synthesized by copolymerizing methyl methacrylate (MMA), GMA, and a series of MMA macromer with different molecular weights), Dong et al. [546] revealed that at the fixed ratio of PLLA/PVDF (50/50) the strain at break could be increased to 500%. Conductive electrospun nanofiber mats based on PLA and electrically conductive polyaniline (PAni) blends were prepared by Picciani et al. [547] with PAni quantities varying from 0 to 5.6 wt%. They showed that the electrospinning process induced miscibility of PLA and PAni either because they were actually miscible or phase separation was retarded due to fast solvent evaporation. 7. PLA ternary or hybrid blends As explained earlier, polymer blending is a pathway to obtain desirable combinations of properties, which are often missing in neat polymers. The achievement of various morphological structures in binary blends is controlled by thermodynamic characteristics, processing and rheological behavior of the polymers during melt blending. Ternary and quaternary blends are much more complex multiphase polymeric systems for which a wide range of microstructures could be achieved. The optimization of the properties of final products may come from the characteristics of the various polymers, while the presence of multiple interfaces with different interfacial features could further affect the properties of multiphase systems. Among ternary blends, various complex microstructures can be tuned by having three polymers or two polymers and additives such as nanoparticles. Beside the processing impact and the rheological characteristics of the components, the obtained morphologies could be determined by the surface energy of each polymer and, hence, the mutual interfacial tension behavior between each two components, as also explained in the Introduction via Eqs. (2) and (3). Several studies have investigated the morphologies and characteristics of PLA-based ternary or hybrid blends via incorporating two other

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

polymers (ternary PLA blends) or blending PLA with a polymer and incorporating nanoparticles (hybrid PLA blends). These investigations are separately discussed below.

7.1. Blends of ternary polymers Different studies have been carried out on a number of ternary polymer blends. In these complex systems, various morphologies could be obtained and, hence, the final properties could be influenced differently by morphology variations, as possibly predicted by theories. The spreading coefficient, calculated via Eq. (3), could be used to predict the types of possible morphologies that are achievable. The spreading coefficient, λBC, indicates the tendency of polymer B to spread over polymer C. A positive value for λBC indicates that polymer B would separate polymers C and A, indicating a complete wetting morphology (twophase contact only). A negative value for λBC indicates partial wetting morphology, where droplets of polymer B are located at the interface of polymers C and A, which results in a three-phase contact. When λBC is equal to zero, morphologies like complete-partial wetting could also be formed, where polymer B could not only be encapsulated in polymer C, but could also be located at the interface of polymers C and A. PLA-based ternary polymer blends have been studied extensively since 2008, when Sarazin et al. [26] from Favis group explored the properties of ternary blends of PLA/TPS/PCL. Since then, a few other studies also focused on improving the properties of PLA/TPS blends via blending with a third polymer that has superior ductility and toughness to overcome the weaknesses of PLA/TPS blends. Similar to Sarazin et al., the majority of these studies were also based on the development of PLA/ TPS/PCL ternary blends [26,548–552]. Sarazin et al. [26] showed that each two-polymer couple (PLA/TPS, TPS/PCL, and PCL/PLA) were immiscible and the synergistic effects caused improvement of the ductility and toughness of the overall system through the addition of a small amount of PCL to PLA/TPS with high glycerol content, although stiffness slightly decreased. In other investigations, PLA-PCL was also grafted with acrylic acid and then mixed with starch. Compared to nongrafted PLA-PCL, smaller droplets of starch were obtained and caused further improvements of the final ductility as well as tensile strength [548]. Carmona et al. [549] showed that using different compatibilizers (i.e., MDI, citric acid and maleic anhydride) improved the PLA and PCL crystallinity; however, only MDI improved the strain at break (to ~65%), tensile strength (to ~12 MPa) and modulus (to ~0.31 GPa) of the PLA/TPS/PCL blends with a fixed ratio of 33/33/33. Mittal et al. [550–551] also showed that the addition of PCL into immiscible PLA/ TPS system improved the intermixing of the polymers within the ternary blends. The PCL addition caused a better dispersion and reduced the domain sizes, specifically TPS droplet sizes in PLA. Davachi et al. [552–553] also looked at the use of triclosan-loaded PLLA nanoparticles on the morphological, thermomechanical, and antibacterial properties of PLA/TPS/PCL ternary blends for biomedical purposes. They showed that the addition of PCL reduced the TPS droplet sizes within the blends and that of triclosan improved the interfacial interaction of the phases. In other works, ternary blends of PLA/TPS with PEG [82,554–556], PBS [557], EVA [558], ESO [85], PEBA [559], and PBAT [120] have been investigated. PEG has been utilized as a plasticizer/compatibilizer and it could improve the interfacial interaction between PLA and TPS and, hence, the ductility (up to 250%) and impact strength (up to 120 J/m) of the final blends [556], specifically when PEG was grafted with maleic anhydride [554]. The PEG molecular weight could also influence the plasticization efficiency of PEG and its migration to the interface of PLA and the TPS compatibilization with PLA [82]. Shi et al. [555] investigated the physical and degradation properties of PLA/TPS blends when using PEG. They claimed that the size of TPS droplets was significantly reduced due to the enhanced compatibility through the incorporation of PEG. Consequently, the ductility and toughness were improved considerably although the tensile strength and stiffness were reduced.

333

Zhen et al. [557] examined ternary blends of PLA/TPS/PBS with a TPS content fixed at 50 wt%. A compatibilizer was used to improve the interfacial affinity between TPS and the polyesters. The ductility and heat deflection temperature of the blends exhibited improvements with increasing PBS content. The effects of maleic anhydride (MA), benzoyl peroxide (BPO) and glycerol on the morphology of PLA/TPS/EVA blends were investigated using reactive extrusion [558]. While the EVA completely wetted starch drops, the plasticization and compatibilization provided a synergistic effect to these blends accompanied by a significant reduction in starch particle size and an increase in interfacial adhesion and, hence, improved ductility (~140%) and impact strength (~80 kJ/m 2 ). ESO was also considered to improve the toughness of PLA/TPS blends as a biobased reactive plasticizer [85]. When using MA grafted starch, the reaction between the epoxy end groups of ESO, MA groups, and carboxylic acid groups on PLA significantly improved the compatibility between these polymers and the ductility and toughness of the PLA/TPS/ESO ternary blends was improved up to 140% and 42 kJ/m2 , respectively, in ternary (80/10/10) blends. Zhou et al. [559] also looked at the properties of PLA/TPS blends when PEBA was used as a partially biobased and fully biodegradable thermoplastic elastomer with outstanding flexibility, high strength, and good processability. Ren et al. [120] also investigated ternary blends of PLA/TPS/PBAT with a fixed TPS content of 50 wt%. They showed that the mechanical properties were enhanced when using a small amount of an anhydride functionalized polyester as a compatibilizer. This was through the size reduction of the dispersed phases, indicative of enhancement of the interfacial interaction between TPS and polyesters. After Ren et al. [120], ternary blends of PLA/PBAT with other polymers were further studied by other investigators [45,560–563]. Kanzawa et al. [560] examined the properties of PLA/PBAT/PC blends prepared by reactive processing via a twin-screw extruder using DCP. They showed that the use of DCP significantly improved the compatibility between PLA and PBAT and provided a much finer PBAT drop morphology. On the other hand, PC and PBAT proved to be miscible. When PC was added during processing, PC immediately covered PBAT drops and they eventually became fully miscible after thermodynamic stabilization. Therefore, in the presence of DCP, finer drops of miscible PBAT/ PC blends appeared in the PLA matrix. In another interesting study [561], PBAT was used as the matrix (50 wt%) and melt blended with PLA (20 wt%) and different lignins (Kraft lignin (KL), methanol soluble lignin (MSL), and methanol insoluble lignin (MIL)). It was illustrated that, compared to the neat PLA/PBAT blend, the ternary blends exhibited more continuous behavior under tensile test, indicating that lignin was bridging the two incompatible PLA/PBAT phases. The KL and MIL blends showed low elongation values, whereas MSL had much higher ductility due to better dispersion and more consistent properties in PLA-PBAT blends. Ravati et al. [45] investigated the morphology and properties of various ternary blends consisting of polymers including PLA, PBAT, PBS, and PCL. The interfacial tension between each two components was estimated. They showed that the morphology could be tuned based on the partial and complete wetting and, hence, the properties could be controlled via the relative compositions. They further showed that [563], in a PBS/PLA/PBAT (33/33/33) blend the morphology was highly continuous with a phase structure dominated by the complete wetting dynamics (i.e., tri-continuous structure). PBAT fully wetted and covered each of the PLA and PBS phases separately. This was in agreement with thermodynamic considerations (i.e., λPBAT/PBS = 0.31, λPBS/PLA = −0.36, λPLA/PBAT = −0.31). This system exhibited large values of the elongation at break (567%), of the Young modulus (1130 MPa), and the impact strength (271 J/m), and a storage modulus (in DMA) about 50% larger than the neat PBS at room temperature. None of the neat materials exhibited these combinations of high properties. The synergy resulted from the tri-continuous structure of the system.

334

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

Other studies on PLA ternary blends are based on PLA/PBS with other polymers such as PHBV [564] and PCL [45,47,563,565]. Zhang et al. [564] showed that significant enhancements of the toughness and flexibility of PLA were achieved by the incorporation of PBS and PHBV without sacrificing the strength and stiffness. Ravati et al. [45,47,563,565] showed that PLA/PBS/PCL blend had a partial wetting microstructure, with self-assembled droplets of the minor phase at the interface. It was demonstrated that by manipulating the phase composition, for example by changing the minor phase component, could modify the morphology such that the droplets of the new minor component were located at the interface between the other two components. The increase in the minor phase content also resulted in the appearance of larger drops at the interface. Annealing of the samples also coarsened the droplet sizes of the minor phase. All these scenarios are depicted in Fig. 15 through schematics, SEM or optical micrographs. Despite the fact that PMMA is a brittle polymer, Yang et al. [566] showed that it can have a toughening effect in blends of PLA/PVDF with PVDF as the matrix. When the PMMA content was 30 wt%, the elongation at break of the ternary blend increased by four times compared with that of the PLA/PVDF blend. However, at a higher PMMA content, this brittle polymer dominated the mechanical properties. As PMMA is mutually miscible with PVDF and PLA the toughening mechanism was attributed to increased entanglements of PVDF, PLA and PMMA chains at the interface. Auliawan et al. [567–568] also explored PLLA ternary blends with PMMA and PEO as well as in the presence of

nanoclay. They found that the three polymers were miscible at low contents of PMMA and PEO in PLLA. The addition of PEO plasticized the PLLA, thus favoring chain mobility of PLLA at lower temperatures, whereas PMMA in the PLLA/PEO matrix reduced the chain mobility and retarded the crystallization of PLLA/PEO. In a series of studies by Zhang et al. [27,569–571], super-toughened ternary PLA blends were prepared by reactive extrusion blending and the authors showed enhancements of the interfacial interactions between the blend components, with moderate levels of strength and modulus. The ternary blend system consisted of PLA, an epoxycontaining elastomer (elastomeric ethylene-butyl acrylate-glycidyl methacrylate terpolymer (EBA-GMA), and zinc ionomer of ethylenemethyacrylic acid copolymer (EMAA-Zn). Dynamic vulcanization occurred during melt extrusion between the epoxy-containing elastomer and zinc ionomer within the PLA matrix. A domain-in-domain (encapsulated) morphology of the ternary blends was observed, where the EMAA-Zn domains were encapsulated by EBA-GMA particles, which were homogeneously dispersed in the PLA matrix. Furthermore, PLA was grafted onto EBA-GMA when the extrusion blending temperature increased to 240 °C and a more effective interfacial compatibilization was achieved. This caused significant increases in the impact strength and strain at break up to 900 J/m and over 200%, respectively, for blends containing 80 wt% PLA as the matrix. In another study [572], ternary blends of PLA, EMA-GMA, and a series of biobased PEBA were fabricated through reactive melt blending to improve the PLA impact strength and

Fig. 15. (a) Schematic and SEM images showing phase compositions and appearance of minor phase droplets at the interface, and optical micrographs showing (b) the appearance of PLA minor phase droplets at the interface in a PBS/PLA/PCL (37.5/12.5/50) blend, (c) the coarsening of the PLA minor phase after annealing of the same blend, and (d) the decrease of the droplet size by reducing the PLA minor phase content in a PBS/PLA/PCL (45.5/4.5/50) blend after annealing (adapted from [45,47,563,565]).

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

ductility. It was also claimed that a super-toughened PLA was developed at an optimized blending weight ratio of 70/20/10 (PLA/EMA-GMA/ PEPA). A partial wetting microstructure with self-assembled droplets of the minor phase (PEBA) at the interface of PLA and EBA-GMA was obtained. The synergistic effect of a good interfacial adhesion and droplets of the minor phase at the interface, followed by a severe shear yielding of the matrix, could have contributed to the improved impact strength (up to 500 J/m) and elongation at break of ~80%. The same investigators studied the toughening effects of a hyper-branched poly(ester-amide) (HBP) and isocyanate-terminated prepolymer of polybutadiene (ITPB) on PLA-based ternary blends [573]. Synergistic effects on the impact strength were observed for the PLA ternary blends with HBP and ITPB, due to the possible physical/chemical interactions between the HBP and ITPB. Super-toughening of PLA was also claimed by Sangeetha et al. [574] when they used EVA and EVOH as blending components. They showed a four-time improvement in ductility when 5 wt% of each EVA and EVOH were blended with PLA; good adhesion occurred between PLA and PVOH through EVA hydrolysis. One of the early studies on PLA ternary blends, done by Wang et al. [575], was on PLA/PHBV/ PEG systems. They showed that the impact strength and elongation at break of the PLA/PHBV blends was significantly improved with the addition of PEG; and in blends containing PEG, the biodegradation in soil was notably accelerated. Super-toughened PLA was also reported when PLA was melt mixed with SEBS and a reactive compatibilizer (EGMA). The EGMA further improved the strain at break and impact strength of PLA/SEBS blends. The thermal stability and service temperature of the blends were further improved by incorporating PC as the third polymer phase, whereas the flexibility and toughness of the blends were not much affected. The morphological structure showed complete wetting of PC and SEBS by the PLA matrix, and SEBS and PC separately contribute to the PLA property improvements [576]. Several other attempts have been made to study various other PLA based ternary blends. Ternary phase diagrams of PLA/PCL/PEO were sketched, analyzed, and discussed Buddhiranon et al. [577]. In another study, a homopolymer PVA was used to improve the compatibilization of partially compatible PPC/PLA blends. PVA was selectively dispersed at the interface between the two continuous phases and in the PLA phase during melt blending. The localization at the interface improved the interfacial bonding and thereby the mechanical properties [311]. Ouyang et al. [578] explored the mechanical properties of PLA with cellulolytic enzyme lignin (CEL) and polyolefin grafted maleic anhydride (PGMA). They claimed that the impact strength and ductility were increased as CEL played a bridging role between PLA and PGMA, although the tensile strength and stiffness decreased. In very recent studies, Zolali et al. [579] showed that PBS, PBAT, EMA, and EMA-GMA could partially wet at the interface of co-continuous PLA/PA11 blends after melt blending and they could play the role of a compatibilizer. The use of EMA was

335

more efficient in increasing the impact strength (up to 4 times) and strain at break (up to 250%) of PLA/PA11 blends. This was through cavitation of partially wet EMA droplets at the interface of co-continous PLA/PA11 blends after loading [579]. Zolali et al. [328] also showed that the use of PEBA as the third polymer in PLA/PA11 con-continuous blends completely wet the PLA and PA11 at their interface and generated a tri-continuous blend. Therefore, a much more deformable interface replaces a rigid PLA/PA11 interface. The further addition of PEO to PLA increased the impact strength to ∼750 J/m (~40 times greater than the co-continuous PLA/PA11 blend). The elongation at break values are also reported as ~3.7, ~230, and ~465%, respectively for, PLA/PEBA/ PA11 (45/10/45), and PLA(PEO)/PEBA/PA11 [45(20)/10/45] [328]. 7.2. PLA blend nanocomposites Different studies have also investigated PLA-based blend nanocomposites. In such systems, not only the final morphology of the blend but also the thermodynamics and interfacial properties between each two components (polymer-polymer and polymer-nanoparticles) would determine the final features of the product. As a result of interfacial interactions, the localization of the nanoparticles could also vary. According to Eq. (2), nanoparticles could either be located in the matrix, secondary polymer, or at the interface of the two phases and thereby the final product properties could be significantly influenced by this selective localization. Fig. 16 depicts how the surface energies and interfacial properties (thermodynamics) and processing and rheological properties of polymer blends (kinetics) could influence the achievement of blend nanocomposite structures with different nanoparticle localization. 7.2.1. PLA blends with nanoclay Several studies explored PLA-based blends with clay nanoparticles. It has been proved that the dispersion and distribution of nanoclay within the polymer blend, as well as the selective localization of the clay nanoparticles are highly dependent on the viscoelastic features of the blend components as well as the processing strategy. In nanoclaybased blend nanocomposites with a high degree of clay dispersion significant enhancements in mechanical, rheological, thermal, and barrier properties could be obtained. This is while the selective localization of clay at the polymer phase interfaces could cause a finer droplet morpohology and minimize droplet coalescence duing processing [581]. Cabedo et al. [582] investigated the behavior of PLA/PCL/clay (kaolinite) blend nanocomposites. The clay was more effective in improving the gas barrier properties of PLA/PCL blends with PLA as the matrix. Salehiyan et al. [583] also investigated the non-linear rheological properties of PLA/PCL/clay (montmorillonite, MMT) under large amplitude oscillatory shear (LAOS) flows. They explained that clay acted as

Fig. 16. Selective localization of silica nanoparticles within (a) PP, the matrix, (c) ethylene octene copolymer (EC), the droplets, and (b) at the interface of two polymer phases under various thermodynamics and kinetics conditions. TEM images adapted from [580].

336

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

Fig. 17. Selective localization of clay nanoparticles within PCL drops for PLA/PCL blend nanocomposites processed via twin-screw extrusion during which kinetics dominated the localization mechanisms (a) and in PLA and at the phase interfaces when thermodynamics dominated the mechanisms after remixing for a longer residence time of 15 min. TEM images adapted from [584].

a compatibilizer and reduced the size of PCL droplets, and proposed a relationship between morphological changes of the blend nanocomposites and linear and non-linear rheological properties. In a recent study [584], PLA/PCL/clay (organo-modified montmorillonite, OMMT, Cloisite 30B) was processed via a twin-screw extruder under high shear and low residence time mixing conditions with a fixed weight ratio of 80/20 of PLA/PCL blends. It was shown that, due to the short time scale of this process, kinetic factors dominated. Thus, clay was located mainly within the PCL phase, although it was thermodynamically more compatible with the PLA matrix. The clay migrated to PLA and to the interface of PLA/PCL when remixed and sufficient residence time was provided. As a consequence, in a blend where kinetics dominated the clay localization, the morphology of the system evolved from drop-type to cocontinuous according to the rheological responses when the OMMT content was beyond 5%. Fig. 17 presents the selective localization of nanoclay in PCL drops as well as in the PLA matrix and at the phase interfaces, where the kinetics and thermodynamics are, respectively, the dominating mechanisms. Nanoclay has also been incorporated in PLA/TPS blends [585–588]. It was shown that the MMT nanoclay could enhance the tensile and

flexural strength of the blends [585]. Also, Cloisite 30B enhanced the thermal stability in fire testing experiments [586] and the water resistance of the blends [587]. Wokada et al. [588] utilized various OMMT clay particles with various hydrophobicities (Cloisite: Na, 30B, 10A, 93A, 20A, 15A). The nanoclay was localized within butylated starch drops and at the interface, except for 20A where the clay was located in both phases and at the interfaces. Although PLA is more hydrophobic than starch, hydrophobic clay such as Cloisite 15A was not dispersed in PLA, possibly due to the lower relative interfacial tension between starch and clay. PLA/PBAT/clay nanocomposites were studied by Jiang et al. [589] who showed that using a twin-screw extruder, the MMT clay was dispersed through the whole blend. Kumar et al. [590] showed a similar localization for Cloisite 20A and obtained a blend nanocomposite with improved thermal stability. Nofar et al. [39] mixed Cloisite 30B within PLA/PBAT blends with a fixed ratio of 75/25 to control the blend morphology under the influence of a shear field. They showed that the nanoclay was localized at the interface of the two phases as predicted from thermodynamics. The nanoclay particles acted as a barrier for droplet coalescence and stabilized the blend morphology under

Fig. 18. TEM images of PLA/PBAT (75/25) blends with 1 and 5 wt% nanoclay (Cloisite 30B). At low clay contents, the nanoparticles are localized only at the interface (a) and at larger clay contents the excessive clay migrates into PLA (b). In (b) droplet coalescence is also prevented by clay particles localized at the interface. TEM images adapted from [39].

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

shearing. They also confirmed that the increase of clay content from 1 to 5 wt% caused the localization of excessive clay in the PLA matrix, due to a stronger thermodynamic affinity of clay to PLA than to PBAT. Fig. 18 illustrates PLA/PBAT blend morphologies with 1 and 5 wt% Cloisite 30B with different selective localizations. It also shows how nanoclay could separate the drops and prevent their coalescence. Although in the work of Nofar et al. [39] amorphous PLA was ultilized, generally the effect of nanoparticles on the crystallization improvement of PLA should also be taken into account [591]. If the nanoparticles localize within a semicrystalline PLA phase, the crystallinity of the final blend system could also be influenced with affects on the final properties. Ternary blends of clay with PLA/PBSA have also been explored extensively in Ray group [592–595]. They studied the microstructure of blend nanocomposites using various types of nanoclay, along with the corresponding thermal and mechanical properties in relation to blend morphology and clay dispersion quality [592]. Ojijo et al. from Ray group showed that at low concentrations, the clay was located within PBSA droplets and at the phase interfaces, primarily due to the lower viscosity of PBSA compared to that of PLA at the processing temperature of 185 °C, indicating the dominant role of kinetics. The thermal and mechanical property enhancements at optimized clay contents were attributed to the strong interfacial interactions between the polymers with clay at the interface of PLA and PBSA [593–594]. Same group also showed that the enzymatic degradation rate could be accelerated or decelerated depending on the chosen clay [595]. Eslami et al. [277] also examined the rheological properties of PLA/PBSA/clay blend nanocomposites after processing via a twin-screw extruder. They revealed that clay platelets were preferentially located at the phase interface with small amounts of clay located within both PLA and PBSA phases. For PLA/PBSA (50/50) blends, where the morphology was nearly cocontinuous, the incorporation of clay platelets changed the morphology from co-continuous to very fine elongated droplet morphology. There are several other studies that have investigated the features of PLA blend clay nanocomposites with other secondary polymers. Using PLA/PP [596] or PLA/PE [597] blends, Nunez et al. showed that without clay compatibilized blends (with various compatibilizers) revealed a higher susceptibility to thermal degradation and higher tensile toughness than those prepared with clay, illustrating the dominant role of compatibilization compared to the role of nanoclay. Ebadi et al. [598–599] showed that Cloisite 15A and 30B nanoparticles tended to be localized in PLA both for PP-rich and PLA-rich blends. However, upon the use of a compatibilizer, all the clay particles were localized at the interface of the two polymers. The mechanical properties appeared to be more dependent on the blend morphology than the blend composition. The localization of clay at the interface significantly improved the impact strength of the blend due to its compatibilizing effect. Also the addition of nanoclay led to a slightly enhanced tensile strength, mainly due to the compatibilizing effect of clay, which also caused a size reduction of the minor phase domains. PLA/natural rubber (NR) systems were also melt blended with various clay types [600–603]. It was shown that the clay particles were mainly localized at the interface of both polymers and acted as a compatibilizer. Moreover, the nanoparticles reduced the minor phase domain sizes, which led to significant improvements of the rheological, thermomechanical, mechanical, and gas barrier properties of the blend nanocomposites and hindered droplet coalescence. Ock et al. [604–605] also mixed three different clays (Cloisite 10A, 20A, and 30B) in PLA/NR blends and investigated the rheological behavior of the nanocomposites. They showed that clay behaved similarly to a compatibilizer through selective localization at the interface. Subsequently, the droplet size of the dispersed phase decreased with increasing clay concentration, and this reduction was more effective with Cloisite 10A, followed by 20A, and then 30B. Cloisite 30B and 15A were also melt mixed in PLA/LLDPE blends using a twinscrew extruder with PLA as the matrix [606–607]. Cloisite 30B resulted in a better exfoliation within the blend and mainly in PLA due to its better affinity to PLA than to LLDPE. Due to hydrophobicity differences

337

between these two clays, the effect of 30B on the refinement of the dispersed phase was much more remarkable than that of 15A. The localization of clay at the interface of two phases resulted in enhanced biodegradability, finer morphology, reduced droplet coalescence, and larger melt elasticity. Moreover, decreasing the PLA content changed the morphology from droplet-type to coarse co-continuity. In contrast, by the addition of each type of clay to PLA/LLDPE blends, the tensile strength as well as elongation at break showed decreasing trends for both PLA-rich and LLDPE-rich systems [606–607]. This was explained by some clay stacks and high stress concentration, which led to large voids during tensile tests. In a similar study [608], it was shown that in the presence of Cloisite 30B a more uniform and finer dispersion of the PE minor phase within the PLA matrix was obtained, mainly due to reduced coalescence of droplets. Zhao et al. [609] investigated the rheological, thermomechanical and mechanical characteristics of PLA/ PHBV/clay blend nanocomposites. Although the neat blends exhibited a Newtonian behavior, blend nanocomposites showed a shearthinning behavior in the presence of 4 wt% Cloisite 30B. The nanocomposites also showed pseudo-solid-like behavior over a wide range of frequency, suggesting strong interactions between the polymers and clay, which restricted molecular relaxation. Derho et al. [610] showed that up to 20 wt%, PEO was miscible with PLA. When adding clay in PLA/PEO blends, the blend nanocomposites revealed limited physical aging and slower PLA/PEO segregation. Nuzzo et al. [611] studied the droplet/matrix blend structures of PLA/PA11 with Cloisite 30B, sepiolite (needle-like clay), and multiwalled carbon nanotubes. In most cases, the nanoparticles were preferably located within the PA minor phase dispersed domains. When exceeding a critical content, the nanoparticles within the minor phase converted the drop-type morphology of PLA/PA11 into a stable highly co-continuous morphology. Rashmi et al. [612] also studied PLA/PA11 blends (80/20) with natural halloysite nanotube (HNT) clays. As thermodynamic rules predicted, HNTs were selectively located in the PA11 phase. Without sacrificing the tensile strength or modulus, the PLA ductility, toughness, and impact strength were significantly improved by the incorporation of PA and HNTs. The strain at break was ~80% and 150% in blends without and with HNT, respectively. Correlations between morphological and rheological properties of PLA/EVA/clay blends were examined by Aghijeh et al. [613–614]. They showed that Cloisite 30B clay was more effective in the refinement of the minor phase domain sizes with more homogeneity than with a compatibilizer. The clay primarily was favorably located within the PLA matrix; however, the addition of a compatibilizer caused clay migration to the interface. Aghijeh et al. explained how the localization of clay could be predicted from rheological data. Singla et al. [615] also introduced a super-toughened PLA/EVA/HNT nanocomposite. HNT remarkably improved the thermal stability, tensile strength and modulus, as well as impact strength of the nanocomposites. HNT was also incorporated in PLA/TPU blends [616]. According to thermodynamic predictions, HNT showed more affinity for localization within PLA. Oliaei et al. [616] showed that HNT was largely located within PLA and at the interface of PLA/TPU. This significantly increased the PLA viscosity and interfacial interactions and changed the droplet-type morphology into a co-continuous one. 7.2.2. PLA blends with carbon nanotubes Blends of PLA/PCL with carbon nanotubes (CNTs) have been studied by several researchers [617–620]. With PCL as the matrix (70 wt%), the CNTs were selectively located within the PCL matrix and at the phase interfaces, and with the increase of CNT content the PLA domain sizes were reduced [617]. When PLA was the matrix, the CNTs were also located in the PCL dispersed phase and the increase in CNT content similarly reduced the droplet size of PCL [619]. With unfunctionalized CNTs, the nanoparticles were only located within the PCL matrix due to the different affinities of the functionalized and un-functionalized CNTs. Only in the case of the interface localization, the CNTs could bring both reinforcing and compatibilization effects to the PCL/PLA blend

338

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

[617]. The direct current (DC) and alternative current (AC) electrical conductivities of the above blend nanocomposites were also measured. The variations of the DC conductivity with CNT concentration allowed the determination of the percolation threshold, which was around 0.98 wt% CNT. The linear dependence of log (σDC) versus p-1/3 (where σDC is the direct current electrical conductivity and p is the aspect ratio of the CNTs) showed the existence of tunneling conduction among CNTs not yet in physical contact [618]. With a fixed content of 1 wt% CNTs, the co-continuous morphology of a PCL/PLA (40/60) blend (with CNTs localized within PCL) exhibited a maximum conductivity [619]. The localization of CNTs and clay in a PLA/PCL (70/30) blend was also examined, and the nanoparticles tended to be localized within PCL domains (and at the interface) for the CNTs and within the PLA matrix (and at the interface), for the clay. These selective localizations were not dependent on the blend ratio, blending sequence, or mixing time. For the clay case, the driving force of the selective localization in PLA was thermodynamics; however, for the CNTs, the kinetics and high viscosity ratio between PLA and PCL were the dominant mechanisms in its localization in PCL. In contrast, with a reduced viscosity ratio, thermodynamics was the main localization factor and, hence, the CNTs were located within the PLA phase. These different selective localizations significantly affected the blend morphology and its final properties. The presence of nanoparticles at the interface also prevented droplet coalescence and stabilized the final blend morphology [619–620]. In PLA/PBAT with different blending ratios, CNTs were mainly located within the PBAT phase for any type of blend morphology, due to high affinity of CNTs to PBAT (i.e., low interfacial tension) [621]. The addition of CNTs into immiscible PLA/EVA blends with a co-continuous morphology was also explored [622]. CNTs tended to be localized at the phase interface, which led to enhancements of the ductility and toughness of the blend nanocomposites while maintaining the stiffness and strength. The differences between using pristine and modified CNTs in PLA/TPU (10/90) blends with TPU as the matrix were also explored [623] and the importance of the CNT chemical modification on the electro active shape memory behavior of the blends was discussed. The double percolation of CNTs in co-continuous PLA/PS blends with selective localization of CNTs was also examined [624]. The blend nanocomposites were prepared firstly by blending of a PS/CNT masterbatch with PLA, and secondly PLA/CNT masterbatch with PS. In the first mixing route, the CNTs were dispersed within the PS phase even after a long mixing time. In the second mixing route, the majority of the CNTs migrated from PLA to the PS phase. These different behaviors were due to the dominant role of thermodynamic driving forces on CNTs migration from PLA to PS or keeping them in PS. As the molding could disrupt the conductivity percolation network due to the particle orientation under shear, the samples were also annealed at elevated temperatures and it was shown that the electrical conductivity was significantly increased due to the CNT reorientation. Lee et al. [625] selectively localized CNTs within the PP matrix of a PP/PLA blend. They showed that the electrical conductivity was enhanced while the percolation threshold was lowered. Multiwalled carbon nanotubes (MWCNTs) were also grafted with lactic-acid to make LA-g-MWCNTs and then dispersed within a PLA/PC blend [626]. The CNT modification increased the electrical conductivity, electromagnetic interference shielding effectiveness, and complex viscosity due to the improved dispersion of the LA-g-MWCNT in the PC/PLA (70/30) blend. Jang et al. [626] claimed that due to a lower interfacial tension between PLA and MWCNTs than that between PC and MWCNTs, the dispersion of the MWCNTs in the PLA phase (dispersed phase) was better than in the PC phase (continuous phase). Park et al. [627] also investigated the morphological, electrical, and rheological properties of PLA/PPC/MWCNT blend nanocomposites. The MWCNTs preferred to be located in the PPC continuous phase due to the lower interfacial tension of the PPC/ MWCNT couple, as well as the lower processing viscosity of the PPC. The improvement in electrical conductivity of PPC/PLA/MWCNT blends

was likely due to the selective localization of the MWCNTs in the PPC phase. 7.2.3. PLA blends with cellulose nanocrystals Arrieta et al. [628–631] extensively investigated the properties of PLA/PHB/freeze-dried cellulose nanocrystals (CNCs) nanocomposites, using melt extrusion followed by film forming. Although agglomerates of CNCs could be observed in the morphology of the neat and blend structures, Arrieta et al. showed that a surface modification of CNCs improved the tensile strength, stiffness, elongation at break, and toughness of the PLA/PHB blends as well as their gas barrier properties, thermal stability, and water resistance. This was achieved by improving the interfacial adhesion between PLA and PHB, as well as due to the CNC reinforcing effect. The modified CNCs, however, had the reverse effect when prepared with the neat PLA alone. CNCs also further accelerated the degradation rate of the final product, while the addition of PHB showed an improvement. Arrieta et al. also incorporated ATBC to facilitate the processing of flexible films. The ATBC further facilitated the modified CNC dispersion and the PLA-PHB interaction, and, consequently, the thermal, mechanical, and barrier properties of the PLA/PHB nanocomposites. They also explored fiber manufacturing through electrospinning. The same group also obtained similar improvements in PLA/PBS blend films in presence of CNCs and surface-modified CNCs [632]. The CNC incorporation in PLA/PBS blends was studied by Zhang et al. [633] who used PBS-g-CNC as a compatibilizer and revealed that the thermal and mechanical properties were improved due to the CNC reinforcing effect and blend morphology changes. Pracella et al. [634] also showed that the CNC addition to PLA/PVAc blends improved the thermal stability and storage modulus. Bitinis et al. [602–603] used CNCs within PLA/NR blends prepared by two methods, i.e., direct extrusion in a Minilab twin-screw extruder and solvent casting combined with extrusion. Following two different surface treatments, the CNCs were located in the PLA and reduced the NR droplet sizes: for another surface modification, the CNCs could be dispersed within the NR drops. None of these studies, however, could successfully present a clear TEM image of CNC dispersed within a polymer; they could mostly show CNC agglomerates. In recent investigation by Heshmati et al. [635] biobased blend nanocomposite systems of PLA/PA11 were prepared using spray dried CNC nanoparticles. The CNCs were separately dispersed within each polymer phase to monitor the CNC selective localization and the blend morphology modification under various processing conditions. It was shown that regardless of the mixing strategy the CNCs preferred to be located in the PA11, which was consistent with thermodynamic predictions. On the other hand, in emulsion-type morphologies, the CNCs did not influence the morphology much; however, in cocontinuous blend morphologies, the CNC addition dramatically reduced the coalescence at CNC contents as low as 1 wt%. Heshmati et al. [636] further revealed that the CNC nanoparticles could change their preferred location from PA11 to PLA irrespective to the mixing strategy when the CNCs were coated by PEO. Heshmati et al. [636] similarly showed that the CNC incorporation did influence the emulsion-type morphology and reduced the droplet size whereas in cocontinuous systems finer morphologies could be obtained. 7.2.4. PLA blends with graphene-based nanoparticles The electrical resistivity of PLA/EVA blends was minimized by the selective localization of graphene oxide (GO) at the phase interface via optimization of the thermodynamics, kinetics, and processing routes [637]. Recently few other studies also examined the properties of PLA/ PCL blends containing graphene-based nanoparticles. Forouharshad et al. [638] evaluated the properties of PLA/PCL blends containing graphite nanoparticles. The presence of graphite at the interface simultaneously enhanced the elongation at break and toughness as well as the tensile strength and modulus [638]. Kelnar et al. [639] also showed that graphite nanoparticles remain within the PCL phase and while influencing the viscosity of the PCL, they support PCL continuity in the

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

co-continuous system while hindering refinement of PCL droplets. Sinha Ray's group [640–641] also showed that when 0.25 wt% graphene was incorporated elongation at break could improve to 44% with wellbalanced modulus and strength, whereas the incorporation of only 0.05 wt% graphene oxide significantly improved the thermal stability and conductivity. The effect of nitrogen-doped graphene on the morphology and properties of PLA/PBS blends was also explored in a recent study [642]. Nitrogen doped graphene was mainly dispersed in PBS and a small amount was located in PLA. The addition of nanoparticles also improved the thermal stability of the blends. According to our search not many investigations have been successfully accomplished with graphene nanoparticles in PLA-based blends and more work is required to understand how graphene nanoparticles could be well dispersed first and how consequently it could improve the final properties and functionality of the blends. 7.2.5. PLA blends with nanosilica Nanosilica (SiO2) is another type of nanoparticle that was incorporated in PLA blends. Li et al. [643] prepared ternary blends of PLA/POE/ SiO2 using melt blending and showed that SiO2 was mainly dispersed within the PLA matrix in a PLA/POE (90/30) blend, and resulted in improvements in mechanical properties. Hydrophobic SiO2 was also used in PLA/TPU (90/10) blends [644]. Yu et al. [644] showed that the addition of silica produced both reinforcing and toughening effects. The incorporation of SiO2 significantly improved the tensile and impact strengths, ductility, and toughness of the PLA/TPU (90/10) blends. With 10 wt% TPU and 2 wt% silica, the strain at break and impact strength were increased up to ~80% and 40 kJ/m2, respectively, without sacrificing the tensile strength or modulus. These improvements were all due to the interfacial interaction enhancement between PLA and TPU that SiO2 generated as a compatibilizer being localized at the interface of the two polymers. In a similar study, Xiu et al. [645] showed that the SiO2 nanoparticles were dispersed in the TPU dispersed phase and at a 5 wt% SiO2 content of a network-like structure of TPU was formed within PLA, which significantly enhanced the impact toughness up to ~55 kJ/m2 (neat PLA/TPU blends showed an impact strength of ~10 kJ/m2). PLA/LDPE blends were also studied in the presence of SiO2 and CaCO3 nanoparticles [646]. Nanosilica, mostly located at the interface, acted as a compatibilizer and improved the phase interactions. It significantly lowered the sizes of the dispersed domains and their homogeneity and thus improved the mechanical properties of the blends. The CaCO3, however, showed less effectiveness and in some cases it reduced the above properties. Vrsaljko et al. [646] claimed that the localization of the CaCO3 nanoparticles strictly in LDPE was the reason for this detrimental effect. Jalili Dil et al. [647] investigated the effects of thermodynamics and kinetics on the localization and migration of micro- and nano-silica particles (modified and unmodified) in PLA/ LDPE blends with high interfacial tensions. According to the thermodynamics considerations, the modified and unmodified micro-/nano-silica particles should be located in the PLA and at the PLA/PE interface. Experiments showed that when unmodified micro-silica or nano-silica were added to PLA/LDPE melts, the particles were located in the PLA and at the phase interface, even when the PLA was the minor phase. However, when the modified micro-silica was used, it was preliminary located within LDPE due to the dominant role of kinetics. The effects of kinetics were explored by, first premixing the particles in LDPE, and then mixing with PLA. When premixed in high viscosity LDPE, the modified and unmodified micro-silica remained in LDPE; however, when the viscosity of LDPE was reduced, the particles migrated to their thermodynamically predicated locations (PLA phase and phase interface) due to the easier diffusion in the low viscosity LDPE compared to high viscosity LDPE. In the case of nanosilica premixed in the high viscosity LDPE, dispersed silica particles moved to the PLA phase after blending the premixed sample with PLA, while their agglomerates remained within the LDPE phase, reflecting the effect of LDPE viscosity and silica particle size on film drainage time. Jalili Dil et al. also investigated another similar system

339

using PBAT instead of LDPE [35,648]. According to thermodynamics predictions, silica particles should be located in the PBAT phase and a direct mixing experiment of all components confirmed this localization. However, when silica was premixed with PLA, after mixing with PBAT, the nanosilica migrated to the phase interface, and the micro-silica remained in the PLA phase when using a high viscosity PLA (H-PLA), but migrated to the interface when a low viscosity PLA (L-PLA) was used. Fig. 19a,c show how, in blends based on L-PLA and H-PLA, the micro-silica could be located in the PBAT droplets when all components were mixed at once. Fig. 19b,d also show how the micro-silica particles migrated from the PLA matrix to the phase interface when the silica was premixed with the PLA. Fig. 20 also shows how the nano-silica could be located in the PBAT droplets when all components were mixed at once for L-PLA based blends, and how they could migrate from PLA matrix to the phase interface when the silica was premixed first with PLA. This migration of nano-silica was not seen for the micro-silica when H-PLA was the matrix. The effect of nanosilica on morphological and rheological properties of miscible PLA/PMMA (50/50) blends was also explored [649]. The nanosilica not only increased the resultant Tg of the blend, but also extended its broadness. While increasing the molecular entanglement density of PLA and PMMA chains, the nanosilica also increased the phase separation temperature of miscible PLA/PMMA blends, which indicated the phase stabilization role of nanosilica. 7.2.6. PLA blends with other nanoparticles TiO2 nanoparticle in PLA/TPU blends was studied by Xiu et al. [650]. Nanoparticles were shown to be selectively localized at the interface surrounding the flexible TPU droplets, leading to a significant improvement in the impact strength (from 3 kJ/m2 for a PLA/TPU (90/10) blend to ~30 kJ/m2 in the same blend containing 15 wt% TiO2). For TiO2 incorporated in PLA/PCL blends, the nanoparticles were primarily dispersed within the PLA phase due to their high affinity with PLA, and they improved the thermal stability of both polymers in the blends [651]. The study on the effects of Boehmit (BAI) nanoparticles (mainly including Al2O3) on PLA/PCL blend properties also showed that in all blend compositions the BAI was selectively localized in the PLA matrix. The elongation at break was significantly improved even beyond 400% when increasing the PCL content with 4 wt% BAI [652]. Jalili Dil et al. [653] further explored the effects of kinetic parameters on the selective localization of cupper nanowires within blends of PLA/LDPE and PLA/PBAT. Due to the nanowires high polarity, they were selectively localized within the most polar phases, which were PLA in the first and PBAT in the second blend systems. This trend was thermodynamically stable when the nanowires were premixed in the most polar phase. In the cases where the nanowires were premixed with less polar phases (LDPE in PLA/ LDPE or PLA in PLA/PBAT), the particles could migrate to the polar phase or phase interfaces only when using high shear rate or long mixing time; hence, both kinetics and thermodynamics determined the selective localization of the nanoparticles. 7.2.7. PLA blends with chitosan Ternary compatible blends of PLA/PVA/chitosan were prepared by oil-in-water emulsion processing [654]. PVA was used as a compatibilizer of the PLA/chitosan emulsion by reducing the interfacial tension, and thereby the stabilization of the emulsion was highly dependent on the presence of PVA. The presence of PVA generated a very high level of adhesion between phases and made these ternary blends promising candidates for the development of new materials composed of PLA and chitosan that have antifungal and antibacterial properties. Zhang et al. [655] made membranes of PLA/PVA/chitosan using solvent casting and found similar improvements in the mechanical and biological properties. Molten PLA/PVA/chitosan ternary blends were prepared for the first time as a novel technique [655]. PVA was similarly used as a compatibilizer and meanwhile acted as a medium for the chitosan dispersion in the PLA matrix. The process allowed the production of

340

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

Fig. 19. SEM images of PLA/PBAT blends with 3 wt% micro-silica. (a, c) all components directly mixed, (b, d) silica premixed with PLA, and then mixed with PBAT. The matrix is L-PLA in (a, b), and H-PLA in (c, d). The scale bars are 2 μm (adapted from [35,648]).

bioactive blends of chitosan with water-insoluble polymers, prepared via conventional processing conditions used for thermoplastics [654]. PLA/ENR/chitosan blends were also prepared using solution casting [656]. The tensile strength and modulus were improved with the addition of chitosan while the elongation at break decreased. Arrieta et al. [657] explored the influence of adding chitosan in PLA/PHB flexible electrospun fibers where ATBC was also used as a plasticizer. The lowest content of chitosan produced better interactions between the PLA and PHB, whereas the increase in chitosan content induced some bead defects in the fibers, which negatively affected the mechanical properties. 8. PLA blend foams Poor foamability of PLA is mainly due to its low melt strength and slow crystallization rates. During foam processes, low melt strength of the polymer could cause cell coalescence and cell-wall rupture [6,658]. Several studies have shown that, during foam extrusion [659–660], foam injection molding [661–664], and bead foaming [665–667], enhanced crystallization rates of PLA can significantly improve the final foaming behaviors (i.e., cell density and expansion ratio). The induced crystallinity can promote the heterogeneous cell nucleation, stabilize the cell growth (without cell wall rupture), and generate closed-cell foams with uniform morphology and controlled expansion ratio [6,658]. It was also confirmed how the physical blowing agent could control the crystallization kinetics of PLA under various pressures and, hence, the foam quality and properties [668–671]. The use of chain extender has also been shown to be one of the promising routes to improve low melt strength and slow crystallization rate of PLA and thereby its foaming properties (foam's expansion ratio, as well as the cell density, with increased closed-cell content)

[664,672–675]. The addition of inorganic particles, such as nanoclay, has also been implemented to enhance low melt strength of PLA and foaming behavior while improving its slow crystallization kinetics [659–660,662–664]. These studies showed that the addition of nanoclay increased the cell density through heterogeneous cell nucleation while controlling the expansion ratio via influencing the melt strength and storage modulus of PLA. Cellular and microcellular foaming of PLA-based blend systems have also been developed mainly to generate scaffolds, tissues, etc. in biomedical applications, as well as to produce light-weight and costeffective products with tailored properties in various commodity and engineering applications. In this section, we review the studies that have been conducted on foaming behavior of PLA samples blended with other PLA resins with different stereochemistries, other biobased and/or biodegradable polymers, other synthetic/nondegradable polymers, and elastomeric polymers. 8.1. Miscible PLA-PLA blend foams Liao et al. [676], Pavia et al. [677], and Jia et al. [678] separately investigated the batch foaming behavior of PLLA/PDLLA, PLLA/PLA, and PLLA/ PDLA miscible blend systems, respectively, where in the latest case stereocomplex crystallites (SC) were generated in the system. Liao et al. and Jia et al. applied carbon dioxide (CO2) as the physical blowing agent, whereas Pavia et al. utilized water. Liao et al. and Pavia et al. tried to develop porous systems appropriate for biomedical applications such as scaffolds and tissue engineering. More specifically, Liao et al. considered that blending PLLA with PDLLA at a proper ratio could cause the development of skinless foams with interconnected porous structure, mainly due to the reduction of the crystallinity of PLLA in presence of

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

341

Fig. 20. AFM (a–b) and SEM (c–d) images of L-PLA/PBAT blends with 3 wt% nanosilica. (a, c) all components directly mixed, (b, d) silica premixed with PLA, and then mixed with PBAT. The scale bars are 2 μm (adapted from [35,648]).

PDLLA. Pavia et al. have also showed that with the addition of PLA to PLLA and reduction of PLLA crystallinity, porous scaffolds could be produced under given processing conditions. On the other hand, in the work of Jia et al., blending of PLLA and PDLA caused the formation of SC crystals with melting temperature ~ 220 °C. They showed that relative to PLLA foams, when PLLA/PDLA (80/20) blends were prepared and foamed, the cell structure uniformity and heat resistance were improved significantly and the cell density increased up to three orders of magnitude. However, it should be noted that the expansion ratio of the final foams was greatly affected, mostly due to the induction of stereocomplex crystallites and hence increased stiffness of the blends. Recently, the group of Chul Park [679] could develop fully green continuously produced extrusion foamed PLA with enhanced foaming features via the introduction of stereocomplex crystals. They showed that stereocomplex crystallites together with synergistically generated new homocrystals significantly increased the cell density and melt strength of PLA foams where high expansion could be acheived without the use of any filler. Microcellular foams were eventually produced with expansion over 30 times when only 3 wt% PDLA was blended with PLA [679]. 8.2. PLA bioblend foams The majority of investigations on the foaming of PLA blends have been conducted on systems where PLA is blended with other biobased and/or biodegradable polymers. These biopolymers are mainly TPS [680–687], PBAT [238,688–694], PHBV [149,609,695–696], PEG [697–700], PBS [701–704], PCL [705–707], PBSA [238,708] and PVOH [709]. Table 1 shows the detailed blend information, type of additives

used, processing methods, blowing agent types, maximum achieved expansion ratios, minimum obtained average cell sizes, and the relevant analysis techniques obtained from the cited studies. Starch has been the most studied case as it is a fully biobased and biodegradable polymer, but it has poor general thermal and mechanical properties. Preechawong et al. [680] investigated how the mechanical and foaming behavior of starch could be improved when blended with PLA. They showed that the addition of PLA up to 30 wt% not only improved the tensile/flexural strength and ductility of starch and its foamed structures, but it also promoted the resistance to water absorption of the starch-based blend foams. Mihai et al. [681] investigated the extrusion foaming behavior of PLA-based blends with TPS using supercritical CO2 as a blowing agent and talc as a cell and crystal nucleating agent. They showed that with the addition of TPS, low density PLA foams with fine open-cell structures could be developed, but only when CO2 concentration exceeded 7 wt%. They also confirmed that in order to obtain a finer cell structure with less open-cell content, interfacial modification of the PLA was necessary. On the other hand, Zhang et al. [682–683] investigated extrusion foaming behavior of starchbased blends with PLA using water as a blowing agent and talc as a cell nucleating agent. They showed that increased water content reduced the melting temperature of the blends. However, to achieve high foam expansion and uniform foam morphology, an optimum water content was required. Hao et al. [684] investigated the foaming behavior of a 60/40 ratio PLA/starch blend, in a batch process, using supercritical CO2 as a blowing agent with the aim of showing that PLA/ starch blends have potentials for medical applications. Lee et al. [685–686] investigated the foaming behavior of tapioca starch nanocomposites blended with 10 wt% PLA. Two different nanoclay types

342

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

Table 1 Studies implemented on PLA bioblend foams. Researchers

Polymer blend systems

blending ratios

Additives

Foam processing

Blowing agent

Minimum average cell size/maximum expansion ratio~

Analysis techniques

Preechawong et al. [680]

PLLA/starch

–

Compression molding

Water

−/6

Tensile & flexural tests/moisture resistance

Mihai et al. [681]

PLA/Starch

Talc

Extrusion

CO2

25 μm/50

Rheology/solubility/DSC/XRD

Zhang et al. [682–683]

PLA/starch

Talc

Extrusion

Water

500 μm/55

Compression test/DSC

Hao et al. [684] Lee et al. [685–686] Teixeira et al. [687] Yuan et al. [688]

PLA/starch PLA/tapioca starch PLA/starch

30/70 10/90 0/100 100/0 67/33 50/50 40/60 30/70 20/80 0/100 60/40 10/90

– Nanoclay (Cloisite NA+ and 30B) Softwood fiber

Batch Extrusion

5 μm/13 300 μm/20

Batch

CO2 Sodium bicarbonate and citric acid Water

Nanosilica

Extrusion

Azodicarbonamide

10–20 μm/3.2

Gas sorption/DSC DSC/XRD/bulk spring index (BSI) and bulk compressibility XRD/tensile and compression tests/moisture resistance FTIR/rheology/DSC

Pilla et al. [689]

PLA/PBAT

Talc

Extrusion

CO2

10 μm/1.8

DSC

Li et al. [690]

PLA/PBAT

Injection

N2

25 μm/1.05

XRD/TEM/DSC/tensile test

Shi et al. [691]

PLA/PBAT

Nanoclay (Cloisite 30B) CaCO3 nanoparticles

Batch

CO2

2 μm/-

Solubility/DSC

Nofar et al. [238] Zhang et al. [692]

PLA/PBAT

–

Batch

CO2

10 μm/8

Rheology/DSC/tensile test

Benzoyl peroxide (BPO)

Extrusion

Azodicarbonamide

100 μm/-

Rheology/DSC

Kang et al. [693]

PLA/PBAT

95/5 90/10 85/15 80/20 70/30

PDLA

b1 μm/-

DSC/tensile/wetting angle

Shi et al. [694]

PLA/PBAT

PDLA

1 μm/-

Rheology/DSC/DMA

Richard et al. [149]

PLA/PHBV

–

Batch

CO2

3 μm/3

DSC

Zhao et al. [695]

PLA/PHBV

–

Injection

N2

75 μm/-

Rheology/DSC/TGA/DMA/tensile test

Zhao et al. [609]

PLA/PHBV

90/10 80/20 70/30 50/50 100/0 75/25 50/50 25/75 0/100 100/0 85/15 70/30 55/45 85/15 70/30 100/0 85/15 70/30 100/0 95/5 90/10 80/20 100/0 90/10 100/0 90/10 80/20 70/30 100/0 80/20 60/40 80/20 100/0 90/10 80/20 70/30 90/10 80/20 70/30 60/40

Solvent Dechloromethane casting/evaporation Batch CO2

Nanoclay (Cloisite 30B) Chitin Nanowhisker

Injection

N2

25 μm/-

Batch

CO2

1.5 μm/2.5

XRD/rheology/DSC/TGA/DMA/tensile test DSC/TGA/rheology/tensile test

– –

Batch Batch

CO2 CO2

15 μm/15 μm/-

FTIR/DSC/DMA Impact and tensile tests/DSC/DMA/POM/rheology

salt

Batch

CO2

7 μm/-

DMA/POM/rheology/TGA

–

Batch

CO2

70 μm/-

Rheology/FTIR/DSC/impact test

Nanoclay (MMT)

Extrusion

CO2

200 μm/1.5

XRD/tensile and impact tests/DSC/rheology

Nanoclay (OMMT) –

Extrusion Batch

Azodicarbonamide CO2

260 μm/2.4 9 μm/10

FTIR/XRD/compression test Rheology

–

Batch

CO2

b2 μm/-

Rheology/DSC

PLA/PBAT

PLA/PBAT

Guan et al. [696] PLA/PHBV Ji et al. [697] Zhang et al. [698]

PLA/PEG PLA/PEG

Chen et al. [699]

PLA/PEG

Wang et al. [700]

PLA/PETG

Ma et al. [701]

PLA/PBS

Zhou et al. [702] Yu et al. [703]

PLA/PBS PLA/PBS

Shi et al. [704]

PLA/PBS

33/67 20/80 100/0 90/10 100/0 45/55 70/30 100/0 90/10 75/25

250 nm/5

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

343

Table 1 (continued) Researchers

Polymer blend systems

Zhao et al. [705–706]

PLA/PCL

Lv et al. [707]

PLA/PCL

Nofar et al. [238] Pradeep et al. [708] Kramschuster et al. [709]

blending ratios

Additives

Foam processing

Blowing agent

Minimum average cell size/maximum expansion ratio~

Analysis techniques

–

Injection

N2/CO2

21 μm/-

DSC/TGA/tensile test/FTIR/DMA/rheology

–

Batch

CO2

b1 μm/-

Tensile test

PLA/PBSA

50/50 90/10 80/20 70/30 60/40 50/50 40/60 30/70 80/20 70/30 60/40 50/50 40/60 30/70 20/80 10/90 75/25

–

Batch

CO2

10 μm/6

Rheology/DSC/tensile test

PLA/PBSA

70/30

talc

Injection

N2

–

DSC/DMA

PLA/PVOH

67/33 Salt (60 wt%) 20/20/salt

Injection + leaching

CO2

5 μm/1.5

TGA

(Cloisite Na+ and 30B) were compounded at different loadings of 1, 3, 5, and 7 wt%. With poor dispersion of both clays, they showed that the cell sizes of the foamed samples were reduced from ~ 1 mm to only 300 μm. They also suggested that the bulk compressibility was somehow decreased with increased clay contents. Teixeira et al. [687] also showed that when starch was blended with a maximum of 33 wt% PLA, the elastic modulus and compressive strength of the foamed structures increased almost 2.5 and 2 times, respectively, and the moisture resistance was improved as well. In most of these studies, starch was the matrix and PLA was used to improve the poor foaming, thermal and mechanical properties of TPS. However, as seen, the enhancements have not been very noticeable even when PLA was selected as the matrix. A few studies have also reported on the foaming behavior of PLA/ PBAT blends. PBAT is now confirmed as a promising biopolymer for blending with PLA as it raises the low melt strength of PLA and improves processability, foamability, toughness and ductility. Consequently, it has also been studied in PLA blend foaming. Yuang et al. [688] used reactive twin-screw foam extrusion with a chemical blowing agent. They showed that the addition of 10 wt% PBAT promoted the PLA foam uniformity as it enhanced its melt strength and, hence, its foamability. Since they used nanosilica as a cell nucleating agent in the blend systems, the lack of investigation on blends without nanosilica makes it difficult to assess the effect of this additive on the foaming behavior of the blends. Yuang et al. also showed that when a small amount of maleic anhydride as a compatibilizer was added, it upgraded the physical and mechanical properties of the blends, but it reduced the cell density of the foamed samples. Using CO2 as a physical blowing agent during extrusion foaming, Pilla et al. [689] reported that the addition of a compatibilizer to PLA/PBAT (45/55) blends slightly increased the cell density of the foamed samples, although it suppressed the total expansion ratio. Li et al. [690] also investigated the effect of nanoclay (Cloisite 30B) content on the foaming behavior of PLA/PBAT (70/30) during microcellular foam injection molding, using N2 as a physical blowing agent. They showed that the clay nanoparticles were thermodynamically preferably located at the interface of the PLA and PBAT droplets, leading to improved interfacial adhesion of the two phases and, thereby, enhanced cell nucleation resulting in smaller cell sizes and higher cell densities (average cell size reduced from around 80 μm in PLA/PBAT to around 20 μm in PLA/PBAT with 5 wt% clay). The tensile strength

and modulus of both solid and microcellular components were also improved with the addition of clay. In another study, using batch foaming and CO2 as a physical blowing agent, Shi et al. [691] explored the effect of 5 wt% CaCO3 nanoparticles on the foaming behavior of PLA/PBAT (90/ 10) blends. They reported that the addition of PBAT as well as CaCO3 improved the cell morphology of PLA foams. The obtained average cell sizes of the foamed PLA, PLA-PBAT, and PLA-PBAT-CaCO3 samples were ~35, 9, and 3 μm, respectively, when saturated for 12 h under a 12 MPa saturation pressure. Nofar et al. [238] evaluated the influence of different PBAT droplet sizes on the microcellular foaming behavior of PLA-PBAT blends, which could lead to the formation of open or closed-cell foam structures. Several other investigations concern the foaming behavior of PLA blends with PHBV. Richard et al. [149] and Guan et al. [696] conducted batch foaming using CO2 as a physical blowing agent. Guan et al. used chitin nanowhiskers. Richard et al. showed that the finest cellular morphologies were obtained at a PHBV content of 25 wt% and the average cell size of the blend foam samples was reduced to ~3 μm under a saturation pressure and temperature of 4.1 MPa and 75 °C, respectively. No foams could be obtained at larger PHBV contents, due to the increased crystallinity of the system. Guan et al. also showed that with a 15 wt% fixed content of PHBV, PLA/PHBV/chitin blend foams exhibited nearly twice the specific strength of PLA/PHBV foams for low amounts (0.5–2 wt%) of chitin nanowhiskers. In two different studies, Zhao et al. [609,695] found that blending PLA with PHBV significantly improved its melt strength, crystallization, and thermomechanical properties; However, using foam injection molding with N2 as a blowing agent, the cell density of the foam samples increased only when 30 wt% PHBV was blended with PLA. However, as the PHBV content increased beyond 30 wt%, the miscibility of the PLA and PHBV became a serious concern, and the foam uniformity was bad. Zhao et al. also showed that the addition of 4 wt% Cloisite 30B further improved the melt strength, crystallization, and thermomechanical properties of the blend system. Subsequently, at the fixed PHBV content of 30 wt%, the addition of clay lowered the cell size from ~75 to ~25 μm. Investigations on PLA-PEG blend foams using CO2 as a blowing agent have been conducted mainly to manufacture scaffolds for biomedical applications. Ji et al. [697] found that with the increase of PEG content, the crystallization rate, elastic modulus, and specifically the degradation rate of the blend system increased and the ductility decreased. The

344

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

degradation rate was further accelerated in the porous blend systems. In blends with 30 wt% PEG, the properties were tailored and a wide range of pore sizes (15–150 μm) could be obtained under various foaming conditions. Zhang et al. [698] showed that with the addition of PEG, the impact and tensile strengths increased and decreased, respectively; moreover, the PLA crystallization was improved, and the shear viscosity of the blends reduced. Consequently, a more porous structure (up to 82% porosity) with finer cell sizes (~15 μm) could be produced. Similar results were observed by Chen et al. [699] who mixed salt (sodium chloride) and then applied leaching. Hence, the porosity was further increased to 85% with much finer cell sizes (~ 7 μm) when 10 wt% PEG and 30 wt% salt were blended with PLA. Wang et al. [700] also blended PLA with PETG while using Joncryl chain extender. The viscoelastic properties of PLA were improved with the addition of PETG and more effectively with the addition of the chain extender. However, the blend foamed samples did not exhibit extraordinary improvements. The finest porous structure (~70 μm) was obtained by blending 20 wt % PETG and 1 wt% chain extender with PLA. PBS is another biodegradable polymer that has been used in conjunction with PLA foaming. Using CO2 as a blowing agent, Ma et al. [701] studied extrusion foaming of PLA-PBS blends and their nanocomposites with 3 wt% MMT nanoclay. The sole addition of PBS could not enhance the foaming behavior of PLA. However, the synergistic effects of 40 wt% PBS and clay could generate more uniform foams with average cell size ~200 μm. Using 20 wt% PBS and clay content up to 4 wt%, Zhou et al. [702] showed that the best foam samples with the finest morphology with an average cell size ~260 μm were achieved when 3 wt% clay was utilized. Consequently, maximum compressive/bending and impact strengths were also observed at this clay loading. Yu et al. [703] showed that storage modulus of PLA was increased in the presence of PBS, and the average cell size was reduced from 16 μm in the neat PLA to a minimum of ~9 μm in blends with 20 wt% PBS. Zhao et al. [705–706] studied the foaming of PLA-PCL blend systems in foam injection molding with N2 and CO2 as blowing agents. The addition of PCL improved the PLA crystallization kinetics and thermal stability. In the solid and foam injection molded samples when using N2, the addition of PCL from 10 to 70 wt% lowered the tensile strength and more detrimentally the modulus of the samples, but it greatly improved the ductility from 4% for both solid and foamed samples to ~800 and 300%, respectively. When CO2 was used as a blowing agent, a uniform foam morphology with fine closed-cell structure (cell size of around 21 μm) was developed at a PCL loading of 30 wt%. Kramschuster et al. [709] investigated the foaming behavior of PLA/PVOH blend systems. They added salt particles (sodium chloride) to the blends and leached the foamed samples in water after the injection process to produce a porous interconnected foam structure as a scaffold for tissue engineering. Extensive mixing of the PLA and PVOH granules via a twin-screw extruder further reduced the dispersed PVOH phase sizes in the PLA matrix. Consequently, the finely dispersed PVOH phase improved the uniformity of the final blend foam morphology.

8.3. PLA blend foams with synthetic/nondegradable polymers There have also been some investigations on the foaming behavior of PLA blended with nondegradable synthetic thermoplastics [710–719]. Table 2 summarizes these studies and the corresponding processing and characterization techniques used. Yao et al. [710] observed that the CO2 solubility in PLLA/PMMA blends was comparable to that observed for the neat PMMA. However, foam morphologies were significantly improved in the blends when compared to the neat PLLA. For the purpose of scaffolding, Velasco et al. [711] investigated the porous interconnectivity of PLA/PMMA blends and found that in blends with lower PLA contents and at higher CO2 pressures, highly porous interconnective scaffolds could be obtained. For a similar application, Kohlhoff et al. [712] studied the foaming behavior of interpenetrated network (IPN) systems of PLA-PS and PLA-PMMA blends at a fixed ratio of 75–25 wt%. They showed that with the addition of PS or PMMA the expansion ratio decreased, but the cell density increased almost by two orders of magnitude. Moreover, since styrene and MMA monomers are good cell-opening media, a porous structure could be developed with up to 90% open-cell content. Zhou et al. [713] also studied the foaming of PLA-PS blends for tissue engineering scaffolds through solid-state foaming. The interconnected porous structure with average pore size of 20–70 μm was created by first foaming the PLA/PS blends and then extracting the PS phase. Liao et al. [714] also illustrated the formation of unique microcellular skin-core structures embedded in PLA/PS blends. The PLA addition on bead foaming behavior of expanded PP (EPP), due to the higher solubility of N-pentane in PLA and PLA lower crystallinity, resulted in more uniform-shaped, higher expanded EPP beads [715]. Bao et al. [716] utilized PLA as the dispersed phase in a PC matrix. They showed that in the neat PLA, microcells were formed, while in the blend systems, nano-cells were generated in the PLA droplets of the blends. The nanocellular foams were also formed in the neat PC and PC matrix. The high crystallinity of the PLA component was effective in the formation of nano-pores in PLA domains. The cell size of nanoscale foams increased with the decreasing crystallinity of the PLA component. Yoon et al. [717] investigated the foaming of PLA-PMMA blends. They demonstrated that it is possible to produce solid state foam precursors by melt blending of a commercial high D-content amorphous PLA and PMMA, followed by impregnation with liquid CO2 and conditioning at ambient pressure in order to adjust the overall CO2 content. 8.4. PLA blend foams with elastomeric polymers Fewer articles have reported studies of the cellular behavior of PLA blended with elastomeric polymers. Due to its biocompatibility, TPU received attentions for blending with PLA and uses in biomedical applications as solid and foamed structures. Probably for the first time, Mi et al. [720] studied the cellular behavior of PLA/TPU blends for tissue engineering scaffolds. Cellular blend structures yielded various ranges of tensile and compressive properties with porosity range of 50–80% that

Table 2 Studies on PLA blend foams with nondegradable synthetic polymers. Researchers

Polymer blend base

Blending ratios

Foam processing

Blowing agent

Minimum average cell size/maximum expansion ratio~

Analysis techniques

Yao et al. [710] Velasco et al. [711] Kohlhoff et al. [712] Zhou et al. [713] Liao et al. [714] Tang et al. [715] Bao et al. [716] Yoon et al. [717] Zhao et al. [718] Zhou et al. [719]

PLLA/PMMA PLA/PMMA PLA/PS & PLA/PMMA PLA/PS PLA/PS PLA/PP PLA/PC PLA/PMMA PLA/HDPE PLA/LDPE

100/0, 25/75, 50/50, 75/25, 0/100 0/100, 10/90, 20/80, 30/70 100/0, 90/10, 75/25, 60/40 50/50 75/25, 60/40, 50/50, 40/60, 25/75 0/100, 5/95, 10/90, 20/80, 30/70 100/0, 25/75, 10/95, 5/95, 0/100 100/0, 80/20, 60/40, 40/60, 20/80, 0/100 95/5, 90/10, 85/15, 80/20 95/5, 90/10, 85/15, 80/20

Batch Batch Batch Batch Batch Batch Batch Batch Batch Batch

CO2 CO2 CO2 CO2 CO2 N-pentane CO2 CO2 CO2 CO2

– 40 μm/2 μm/16 20 μm/16 – 20 μm/45 50 nm/50 μm/20 31 μm/40 21 μm/29

DSC/TGA/solubility NMR/DSC Rheology Solubility Rheology Solubility/DSC DSC/DMA DSC/DMA/solubility DSC/POM/rheology DSC/POM. Rheology

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

could be used in multiple scaffold applications. Barmouz et al. [721–722] have also recently investigated the foaming behavior of PLA/TPU blends. Song et al. [723] also investigated porous PLA-TPU biocompatible shape-memory blend systems having TPU as the major phase. They showed that blends with 80 wt% TPU and neat TPU produced the smallest pore sizes (~2 μm) and highest pore density. Foamed blends with 50 and 80 wt% TPU and neat TPU also exhibited shape memory features when the foams were annealed. Jia et al. [724] explored the foaming behavior of PLA/EVA blends. However, they did not consider the influence of blending EVA with PLA. Han et al. [725] explored the effect of the addition of PLA to NBR on the foaming behavior of their blends. The foamed samples exhibited a similar cell structure and foaming ratio to the neat NBR when the PLA content increased to 30 wt%; however, the cell formation was considerably reduced when the added PLA content exceeded 30 wt%. 9. Conclusion, challenges and future perspectives In this article, we reviewed the attempts to develop PLA-based blends and compared the composition-processing-morphology-properties relationships developed so far for various applications. This includes an overview of the investigations that have been conducted on (i) miscible blends of PLLA and PDLA; (ii) binary immiscible/miscible blends of PLA with other thermoplastics; (iii) multifunctional ternary PLA blends using a third polymer or hybrid systems with fillers such as nanoparticles; and (iv) PLA-based blend foam systems. According to the literature, the interest of developing PLA-based blends with better performance and lower cost is growing every year and researchers are eagerly seeking more efficient and multifunctional products based on PLA. This is driven by the global concerns regarding energy and environmental issues which are growing with time. The lack of biodegradability of conventional plastics which are based on non-renewably petroleum makes the development of bio-based PLA products with desired properties a priority not only for academicians but also for plastics manufacturing companies. Also, the biocompatibility and non-toxic features of PLA render its compounds promising candidates for biomedical applications. According to the statistics shown in this report, the research on PLAbased blends has grown dramatically in different areas during the last decade. Among binary systems, blending PLA with biopolymers has been of greater interest to researchers due to the full bio-feature of the final products. Among these biopolymers, blends of PLA with PCL, starch, PHA, and PBAT have been investigated more than blends with other biopolymers. PLA blends with non-biopolymers such as elastomeric thermoplastics, rubber and TPU have also been largely investigated. In the majority of these studies, specifically for immiscble blends, the main concern in dealing with emulsion-type morphologies

345

has been to minimize the interfacial tension, hence creating a strong interfacial interaction. Different types of additives, compatibilizers, copolymers, cross-linkers and chain extenders have been tried with various PLA-based blends and significant improvements have been achieved in some cases. In some of these blends the strain at break and impact strength could profoundly be enhanced while the strength and stiffness could remain unchanged. Table 3 reports important mechanical properties obtained in various studies in PLAbased blends with other biopolymers where PLA is the main phase, i.e., the matrix, with a maximum of 30 wt% of the dispersed phase content. The major purpose of these studies, has been to improve the ductility and impact properties of PLA products with minimum losses in strength and modulus. However, one should keep in mind that the majority of the noted additives are expensive and may not be practically usable in commodity or engineering applications. Few studies have also discussed that with processing optimization proper improvements could be obtained without the incorporation of any additive. The biodegradability and biocompatibility of the PLA-based blend systems have also revealed different behaviors with and without the presence of various additives that could be tailored for different applications and requirements. Moreover, the development of ternary and hybrid blends is growing more aggressively due to the possible introduction of further functional properties to the blend. These functional properties could be obtained due to the synergy resulting from interfacial interactions of different phases in the blend; hence, properties could differently be influenced. The selective localization of nanoparticles together with their influence on the viscoelastic features of the blends could differently influence the blend morphology, properties and new generated functionalities depending on the type of filler. For blend nanocomposites, the use of nanoclay has been explored more extensively due to the high performance of clay nanoplatelets, its low cost, and its easier dispersion in polymers according to the existence of various modified clays. Layered clay could also improve the barrier properties of PLA, which is important for packaging applications. The use of graphene-based nanoparticles and cellulose nanocrystals are also the new trends of PLA blend nanocomposites for various applications. The development of PLA blend cellular and microcellular foams has also turned to be an important research area to produce lighter products at lower costs and biodegradation features. The influence of stereocomplex crystals on the improvement of foam products without the use of any additive has been of one of the major findings in the recent years. Moreover, using three different foam processing, i.e., extrusion, injection molding, and bead foaming, number of studies have looked at the influence of the existence of the second phase on PLA's foaming behavior while taking the advantage of the second phases' features in improving the drawbacks of PLA.

Table 3 Important acheivements in mechanical properties of various PLA-based blends with other biopolymers. Blend type

Dispersed phase content (wt%)

Additive type

Strength (MPa)

Modulus (MPa)

Elongation at break (%)

Impact strength

Ref.

PLA - starch PLA - PHB PLA - PHBV PLA - PCL PLA - PBAT PLA - PBAT PLA - PBAT PLA - PBAT PLA - PBAT PLA - PBSA PLA - PBSA PLA - PBS PLA - PBS PLA - PBS PLA - PBS PLA - PPC

10 20 20 20 25 20 25 20 10 20 25 20 20 10 30 30

ESO – – – – – ATBC BOZ, PA EMA-GMA Joncryl – DCP DCP LTI MDI MA

43 36 42 57 35 45 18 45 44 110 42 49 80 60 34 40

2510 2720 2500 2900 1400 1200 62 – 1700 3100 1350 2530 –

140 27 230 142 265 300 250 515 320 200 150 250 200 240 285 164

42 kJ/m2 120 kJ/m2 150 kJ/m2 25 J/m 9 J/m – – – 62 kJ/m2 20 kJ/m2 5 J/m 30 kJ/m2 – 70 kJ/m2 – 40 kJ/m2

[85] [159] [180] [214] [238] [239] [241] [246] [255] [274] [238] [285] [287] [288] [290] [310]

1288

346

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

In this context, several petroleum based plastics such as PS, PET, PE, and PP could be replaced within years by PLA compounds for various commodity and engineering applications. Besides energy and environmental concerns, this trend is due to price reductions of commercial PLAs, efforts to solve PLA's shortcomings via blending or other possible routes, and the introduction of PLA-based products with better performance and desired properties. Nevertheless, extensive research still needs to be carried out to develop PLA-based compounds/blends with superior performance, less shortcomings, lower cost and desirable multifunctional properties.

References [1] D. Garlotta, A literature review of poly (lactic acid), J. Poly. Environ. 9 (2002) 63–84, https://doi.org/10.1023/A:1020200822435. [2] R.G. Sinclair, The case for polylactic acid as a commodity packaging plastic, J. Macromol. Sci., Part A: Pure Appl. Chem. 33 (1996) 33–585, https://doi.org/10. 1080/10601329608010880. [3] D.W. Grijpma, A.J. Pennings, (Co)polymers of L-lactide, 2. Mechanical properties, Macromol. Chem. Phys. 195 (1994) 1649–1663, https://doi.org/10.1002/macp. 1994.021950516. [4] R. Auras, B. Harte, S. Selke, An overview of polylactides as packaging materials, Macromol. Biosci. 4 (2014) 835–864, https://doi.org/10.1002/mabi.200400043. [5] R.E. Drumright, P.R. Gruber, D.E. Henton, Polylactic acid technology, Adv. Mater. 12 (2000) 1841–1846, https://doi.org/10.1002/1521-4095(200012)12:23b1841:: AID-ADMA1841N3.0.CO;2-E. [6] M. Nofar, C.B. Park, Poly (lactic acid) foaming, Prog. Polym. Sci. 39 (2014) 1721–1741, https://doi.org/10.1016/j.progpolymsci.2014.04.001. [7] B. Gupta, N. Revagade, J. Hilborn, Poly (lactic acid) fiber: an overview, Prog. Polym. Sci. 32 (2007) 455–482, https://doi.org/10.1016/j.progpolymsci.2007.01.005. [8] J. Lunt, Large-scale production, properties and commercial applications of polylactic acid polymers, Polym. Degrad. Stab. 59 (1998) 145–152, https://doi. org/10.1016/S0141-3910(97)00148-1. [9] P. Saini, M. Arora, M.N.V.R. Kumar, Poly(lactic acid) blends in biomedical applications, Adv. Drug Deliv. Rev. 107 (2016) 47–59, https://doi.org/10.1016/j.addr. 2016.06.014. [10] A.G. Mikos, M.D. Lyman, L.E. Freed, R. Langer, Wetting of poly(L-lactic acid) and poly(D,L-lactic-co-glycolic acid) foams for tissue culture, Biomaterials 15 (1994) 55–58, https://doi.org/10.1016/0142-9612(94)90197-X. [11] Y. Jung, S.S. Kim, H.K. Young, S.H. Kim, B.S. Kim, S. Kim, H.K. Soo, A poly(lactic acid)/calcium metaphosphate composite for bone tissue engineering, Biomaterials 26 (2005) 6314–6322, https://doi.org/10.1016/j.biomaterials.2005.04. 007. [12] L.T. Lim, R. Auras, M. Rubino, Processing technologies for poly (lactic acid), Prog. Polym. Sci. 33 (2008) 820–852, https://doi.org/10.1016/j.progpolymsci.2008.05. 004. [13] S. Saeidlou, M.A. Huneault, H. Li, C.B. Park, Poly (lactic acid) crystallization, Prog. Polym. Sci. 37 (2012) 1657–1677, https://doi.org/10.1016/j.progpolymsci.2012. 07.005. [14] R.M. Rasal, A.V. Janorkar, D.E. Hirt, Poly (lactic acid) modifications, Prog. Polym. Sci. 35 (2010) 338–356, https://doi.org/10.1016/j.progpolymsci.2009.12.003. [15] J. Dorgan, J. Janzen, M. Clayton, S. Hait, D. Knauss, Melt rheology of variable Lcontent poly(lactic acid), J. Rheol. 49 (2005) 607–619, https://doi.org/10.1122/1. 1896957. [16] J. Dorgan, J. Williams, Melt rheology of poly(lactic acid), entanglement and chainarchitecture effects, J. Rheol. 43 (1999) 1141–1155, https://doi.org/10.1122/ 1.551041. [17] G. Theryo, F. Jing, L.M. Pitet, M.A. Hillmyer, Tough polylactide graft copolymers, Macromolecules 43 (2010) 7394–7397, https://doi.org/10.1021/ma101155p. [18] D.W. Grijpma, G.J. Zondervan, A.J. Pennings, High molecular weight copolymers of L-lactide and ε-caprolactone as biodegradable elastomeric implant materials, Polym. Bull. 25 (1991) 327–333, https://doi.org/10.1007/BF00316902. [19] C.A.P. Joziasse, M.D.C. Topp, H. Veenstra, D.W. Grijpma, A.J. Pennings, Supertough poly(lactide)s, Polym. Bull. 33 (1994) 599–605, https://doi.org/10.1007/ BF00296170. [20] D.W. Grijpma, R.D.A. Van Hofslot, H. Supèr, A.J. Nijenhuis, A.J. Pennings, Rubber toughening of poly(lactide) by blending and block copolymerization, Polym. Eng. Sci. 34 (1994) 1674–1684, https://doi.org/10.1002/pen.760342205. [21] Z. Fan, Z. Xu, H. Niu, N. Gao, Y. Guan, C. Li, Y. Dang, X. Cui, X.L. Liu, Y. Duan, H. Li, X. Zhou, P.H. Lin, J. Ma, J. Guan, An injectable oxygen release system to augment cell survival and promote cardiac repair following myocardial infarction, Sci. Rep. 8 (2018) 1371–1398, https://doi.org/10.1038/s41598-018-19906-w. [22] Z.Z. Fan, M. Fu, Z. Xu, B. Zhang, Z. Li, H. Li, et al., Sustained release of a peptide-based matrix metalloproteinase-2 inhibitor to attenuate adverse cardiac remodeling and improve cardiac function following myocardial infarction, Biomacromolecules 18 (2017) 2820–2829, https://doi.org/10.1021/acs.biomac.7b00760. [23] C.W. Macosko, Morphology development and control in immiscible polymer blends, Macromol. Symp. 149 (2000) 171–184, https://doi.org/10.1002/15213900(200001)149:1b171::aid-masy171N3.0.co;2-8. [24] B.D. Favis, Polymer alloys and blends: recent advances, Can. J. Chem. Eng. 69 (1991) 619–625, https://doi.org/10.1002/cjce.5450690303.

[25] L. Yu, K. Dean, L. Li, Polymer blends and composites from renewable resources, Prog. Polym. Sci. 31 (2006) 576–602, https://doi.org/10.1016/j.progpolymsci. 2006.03.002. [26] P. Sarazin, G. Li, W.J. Orts, B.D. Favis, Binary and ternary blends of polylactide, polycaprolactone and thermoplastic starch, Polymer 49 (2008) 599–609, https:// doi.org/10.1016/j.polymer.2007.11.029. [27] H. Liu, W. Song, F. Chen, L. Guo, J. Zhang, Interaction of microstructure and interfacial adhesion on impact performance of Polylactide (PLA) ternary blends, Macromolecules 44 (2011) 1513–1522, https://doi.org/10.1021/ ma1026934. [28] V. Arrighi, J.M.G. Cowie, S. Furhman, Y. Abdelsallem, I.Isayev. Avraam., Miscibility criterion in polymer blend and its determination, Encyclopedia of Polymer Blends, Wiley-VCH Verlag GmbH & Co, Weinheim 2016, pp. 153–198, https://doi.org/10. 1002/9783527805204.ch5. [29] B.D. Favis, D. Therrien, Factors influencing structure formation and phase size in an immiscible polymer blend of polycarbonate and polypropylene prepared by twinscrew extrusion, Polymer 32 (1991) 1474–1481, https://doi.org/10.1016/00323861(91)90429-m. [30] B.D. Favis, J.P. Chalifoux, The effect of viscosity ratio on the morphology of polypropylene/polycarbonate blends during processing, Polym. Eng. Sci. 27 (1987) 1591–1600, https://doi.org/10.1002/pen.760272105. [31] C.E. Scott, C.W. Macosko, Model experiments concerning morphology development during the initial stages of polymer blending, Polym. Bull. 26 (1991) 341–348, https://doi.org/10.1007/bf00587979. [32] U. Sundararaj, C.W. Macosko, A. Nakayama, T. Inoue, Milligrams to kilograms: an evaluation of mixers for reactive polymer blending, Polym. Eng. Sci. 35 (1995) 100–114, https://doi.org/10.1002/pen.760350113. [33] A. Souza, N. Demarquette, Influence of coalescence and interfacial tension on the morphology of PP/HDPE compatibilized blends, Polymer 43 (2002) 3959–3967, https://doi.org/10.1016/s0032-3861(02)00223-9. [34] A. Maani, B. Blais, M.-C. Heuzey, P.J. Carreau, Rheological and morphological properties of reactively compatibilized thermoplastic olefin (TPO) blends, J. Rheol. 56 (2012) 625–647, https://doi.org/10.1122/1.3700966. [35] E.J. Dil, B.D. Favis, Localization of micro- and nano-silica particles in heterophase poly(lactic acid)/poly(butylene adipate-co-terephthalate) blends, Polymer 76 (2015) 295–306, https://doi.org/10.1016/j.polymer.2015.08.046. [36] J. Huitric, M. Moan, P.J. Carreau, N. Dufaure, Effect of reactive compatibilization on droplet coalescence in shear flow, J. Non-Newtonian Fluid Mech. 145 (2007) 139–149, https://doi.org/10.1016/j.jnnfm.2007.06.001. [37] P.V. Puyvelde, A. Vananroye, R. Cardinaels, P. Moldenaers, Review on morphology development of immiscible blends in confined shear flow, Polymer 49 (2008) 5363–5372, https://doi.org/10.1016/j.polymer.2008.08.055. [38] S. Wu, Polymer Interface and Adhesion, Marcel Dekker, New York, 1982. [39] M. Nofar, M.-C. Heuzey, P. Carreau, M. Kamal, Effects of nanoclay and its localization on the morphology stabilization of PLA/PBAT blends under shear flow, Polymer 98 (2016) 353–364, https://doi.org/10.1016/j.polymer.2016. 06.044. [40] M. Sumita, K. Sakata, S. Asai, K. Miyasaka, H. Nakagawa, Dispersion of fillers and the electrical conductivity of polymer blends filled with carbon black, Polym. Bull. 25 (1991) 265–271, https://doi.org/10.1007/bf00310802. [41] A. Taghizadeh, B.D. Favis, Carbon nanotubes in blends of polycaprolactone/thermoplastic starch, Carbohydr. Polym. 98 (2013) 189–198, https://doi.org/10.1016/j. carbpol.2013.05.024. [42] W.D. Harkins, A. Feldman, Films. The spreading of liquids and the spreading coefficient, J. Am. Chem. Soc. 44 (1922) 2665–2685, https://doi.org/10.1021/ ja01433a001. [43] W.D. Harkins, A general thermodynamic theory of the spreading of liquids to form duplex films and of liquids or solids to form monolayers, J. Chem. Phys. 9 (1941) 552–568, https://doi.org/10.1063/1.1750953. [44] B.P. Binks, J.H. Clint, Solid wettability from surface energy components: relevance to pickering emulsions, Langmuir 18 (2002) 1270–1273, https://doi.org/10.1021/ la011420k. [45] S. Ravati, B.D. Favis, Tunable morphologies for ternary blends with poly(butylene succinate): partial and complete wetting phenomena, Polymer 54 (2013) 3271–3281, https://doi.org/10.1016/j.polymer.2013.04.005. [46] J. Zhang, S. Ravati, N. Virgilio, B.D. Favis, Ultralow percolation thresholds in ternary cocontinuous polymer blends, Macromolecules 40 (2007) 8817–8820, https://doi. org/10.1021/ma0716480. [47] S. Ravati, B.D. Favis, Interfacial coarsening of ternary polymer blends with partial and complete wetting structures, Polymer 54 (25) (2013) 6739–6751, https:// doi.org/10.1016/j.polymer.2013.10.009. [48] P.R. Gruber, E.S. Hall, J.H. Kolstad, M.L. Iwen, R.D. Benson, R.L. Borchardt, Continuous Process for Manufacture of Lactide Polymers With Controlled Optical Purity, 1992 (US5142023A). [49] W. Ding, T. Kuboki, A. Wong, C.B. Park, M. Sain, Rheology, thermal properties, and foaming behavior of high d-content polylactic acid/cellulose nanofiber composites, RSC Adv. 5 (2015) 91544–91557, https://doi.org/10.1039/c5ra16901a. [50] Y. Ikada, K. Jamshidi, H. Tsuji, S.H. Hyon, Stereocomplex formation between enantiomeric poly(lactides), Macromolecules 20 (1987) 904–906, https://doi.org/10. 1021/ma00170a034. [51] T. Okihara, M. Tsuji, A. Kawaguchi, K.-I. Katayama, H. Tsuji, S.-H. Hyon, et al., Crystal structure of stereocomplex of poly( L -lactide) and poly(D-lactide), J. Macromol. Sci., Part B: Phys. 30 (1–2) (1991) 119–140, https://doi.org/10. 1080/00222349108245788. [52] H. Tsuji, Poly(lactic acid) stereocomplexes: a decade of progress, Adv. Drug Deliv. Rev. 107 (2016) 97–135, https://doi.org/10.1016/j.addr.2016.04.017.

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360 [53] H. Tsuji, Poly(lactide) stereocomplexes: formation, structure, properties, degradation, and applications, Macromol. Biosci. 7 (2007)https://doi.org/10.1002/mabi. 200700275 (1299–1299). [54] K. Fukushima, Y. Kimura, Stereocomplexed polylactides (Neo-PLA) as highperformance bio-based polymers: their formation, properties, and application, Polym. Int. 55 (2006) 626–642, https://doi.org/10.1002/pi.2010. [55] Y. Jing, C. Quan, B. Liu, Q. Jiang, C. Zhang, A mini review on the functional biomaterials based on poly(lactic acid) Stereocomplex, Polym. Rev. 56 (2) (2016) 262–286, https://doi.org/10.1080/15583724.2015.1111380. [56] H. Tsuji, T. Tsuruno, Water vapor permeability of poly(L-lactide)/poly(D-lactide) stereocomplexes, Macromol. Mater. Eng. 295 (2010) 709–715, https://doi.org/10. 1002/mame.201000071. [57] E.W. Fischer, H.J. Sterzel, G. Wegner, Investigation of the structure of solution grown crystals of lactide copolymers by means of chemical reactions, Aktuelle Probleme Der Polymer-Physik IV Akt, Prob. Der. Polym. Phys. (1973) 980–990, https://doi.org/10.1007/978-3-642-47050-9_24. [58] J.-R. Sarasua, R.E. Prudhomme, M. Wisniewski, A.L. Borgne, N. Spassky, Crystallization and melting behavior of polylactides, Macromolecules 31 (1998) 3895–3905, https://doi.org/10.1021/ma971545p. [59] J.-R. Sarasua, N.L. Rodríguez, A.L. Arraiza, E. Meaurio, Stereoselective crystallization and specific interactions in polylactides, Macromolecules 38 (2005) 8362–8371, https://doi.org/10.1021/ma051266z. [60] J. Sarasua, A.L. Arraiza, P. Balerdi, I. Maiza, Crystallinity and mechanical properties of optically pure polylactides and their blends, Polym. Eng. Sci. 45 (2005) 745–753, https://doi.org/10.1002/pen.20331. [61] G.L. Loomis, J.R. Murdoch, K.H. Gardner, Polylactide stereocomplexes, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) 31 (1990) 55. [62] H. Tsuji, F. Horii, M. Nakagawa, Y. Ikada, H. Odani, R. Kitamaru, Stereocomplex formation between enantiomeric poly(lactic acid)s. 7. Phase structure of the stereocomplex crystallized from a dilute acetonitrile solution as studied by highresolution solid-state carbon-13 NMR spectroscopy, Macromolecules 25 (1992) 4114–4118, https://doi.org/10.1021/ma00042a011. [63] Y. Wang, J.F. Mano, Stereocomplexation and morphology of enantiomeric poly(lactic acid)s with moderate-molecular-weight, J. Appl. Polym. Sci. 107 (2007) 1621–1627, https://doi.org/10.1002/app.27260. [64] S.C. Schmidt, M.A. Hillmyer, Polylactide stereocomplex crystallites as nucleating agents for isotactic polylactide, J. Polym. Sci. B Polym. Phys. 39 (2001) 300–313, https://doi.org/10.1002/1099-0488(20010201)39:3b300::aid-polb1002N3.3.co;2d. [65] H. Yamane, K. Sasai, Effect of the addition of poly(d-lactic acid) on the thermal property of poly(l-lactic acid), Polymer 44 (2003) 2569–2575, https://doi.org/10. 1016/s0032-3861(03)00092-2. [66] D. Maillard, R.E. Prud'Homme, Differences between crystals obtained in PLLA-rich or PDLA-rich stereocomplex mixtures, Macromolecules 43 (2010) 4006–4010, https://doi.org/10.1021/ma902625p. [67] H. Tsuji, Y. Ikada, Stereocomplex formation between enantiomeric poly(lactic acid) s. XI. Mechanical properties and morphology of solution-cast films, Polymer 40 (1999) 6699–6708, https://doi.org/10.1016/s0032-3861(99)00004-x. [68] Y. Doi, A. Steinbuchel, Polyesters III: applications and commercial products, Biopolymers, 4th editionJohn Wiley-VCH, Weinheim, Germany, 2002 , (978-3-52730225-3). [69] Y. Srithep, D. Pholharn, L.-S. Turng, O. Veang-In, Injection molding and characterization of polylactide stereocomplex, Polym. Degrad. Stab. 120 (2015) 290–299, https://doi.org/10.1016/j.polymdegradstab.2015.07.017. [70] S. Saeidlou, M.A. Huneault, H. Li, P. Sammut, C.B. Park, Evidence of a dual network/ spherulitic crystalline morphology in PLA stereocomplexes, Polymer 53 (2012) 5816–5824, https://doi.org/10.1016/j.polymer.2012.10.030. [71] S. Saeidlou, M.A. Huneault, H. Li, C.B. Park, Poly(lactic acid) stereocomplex formation: application to PLA rheological property modification, J. Appl. Polym. Sci. 131 (2014) 41073–41081, https://doi.org/10.1002/app.41073. [72] X.-F. Wei, R.-Y. Bao, Z.-Q. Cao, W. Yang, B.-H. Xie, M.-B. Yang, Stereocomplex crystallite network in asymmetric PLLA/PDLA blends: formation, structure, and confining effect on the crystallization rate of homocrystallites, Macromolecules 47 (2014) 1439–1448, https://doi.org/10.1021/ma402653a. [73] H. Tsuji, I. Fukui, Enhanced thermal stability of poly(lactide)s in the melt by enantiomeric polymer blending, Polymer 44 (2003) 2891–2896, https://doi.org/10. 1016/s0032-3861(03)00175-7. [74] S. Jacobsen, H.G. Fritz, Filling of poly(lactic acid) with native starch, Polym. Eng. Sci. 36 (1996) 2799–2804, https://doi.org/10.1002/pen.10680. [75] G. Biresaw, C.J. Carriere, Correlation between mechanical adhesion and interfacial properties of starch/biodegradable polyester blends, J. Polym. Phys. Part. B 39 (2001) 920–930, https://doi.org/10.1002/polb.1067.abs. [76] T. Ke, S.X. Sun, P. Seib, Blending of poly(lactic acid) and starches containing varying amylose content, J. Appl. Polym. Sci. 89 (2003) 3639–3646, https://doi.org/10. 1002/app.12617. [77] T. Ke, X. Sun, Effects of moisture content and heat treatment on the physical properties of starch and poly(lactic acid) blends, J. Appl. Polym. Sci. 81 (2001) 3069–3082, https://doi.org/10.1002/app.1758. [78] T. Ke, X. Sun, Melting behavior and crystallization kinetics of starch and poly(lactic acid) composites, J. Appl. Polym. Sci. 89 (2003) 1203–1210, https://doi.org/10. 1002/app.12162. [79] J.-F. Zhang, X. Sun, Mechanical properties and crystallization behavior of poly(lactic acid) blended with dendritic hyperbranched polymer, Polym. Int. 53 (2004) 716–722, https://doi.org/10.1002/pi.1457. [80] J.W. Park, D.J. Lee, E.S. Yoo, S.S. Im, Biodegradable polymer blends of poly (lactid acid) and starch, Korea Polym. J. 7 (1999) 93–101.

347

[81] M. Kozlowski, R. Masirek, E. Piorkowska, M. Gazicki-Lipman, Biodegradable blends of poly(L-lactide) and starch, J. Appl. Polym. Sci. 105 (2007) 269–277, https://doi. org/10.1002/app.26088. [82] Y. Yu, Y. Cheng, J. Ren, E. Cao, X. Fu, W. Guo, Plasticizing effect of poly(ethylene glycol)s with different molecular weights in poly(lactic acid)/starch blends, J. Appl. Polym. Sci. 132 (2015) 41808, https://doi.org/10.1002/app.41808. [83] P. Jariyasakoolroj, S. Chirachanchai, Silane modified starch for compatible reactive blend with poly(lactic acid), Carbohydr. Polym. 106 (2014) 255–263, https://doi. org/10.1016/j.carbpol.2014.02.018. [84] C.L. Jun, Reactive blending of biodegradable polymers: PLA and starch, J. Polym. Environ. 8 (2000) 33–37, https://doi.org/10.1023/A:1010172112118. [85] Z. Xiong, Y. Yang, J. Feng, X. Zhang, C. Zhang, Z. Tang, et al., Preparation and characterization of poly(lactic acid)/starch composites toughened with epoxidized soybean oil, Carbohydr. Polym. 92 (2013) 810–816, https://doi.org/10.1016/j.carbpol. 2012.09.007. [86] H. Wang, X. Sun, P. Seib, Strengthening blends of poly(lactic acid) and starch with methylenediphenyl diisocyanate, J. Appl. Polym. Sci. 82 (2001) 1761–1767, https:// doi.org/10.1002/app.2018.abs. [87] H. Wang, X. Sun, P. Seib, Mechanical properties of poly(lactic acid) and wheat starch blends with methylenediphenyl diisocyanate, J. Appl. Polym. Sci. 84 (2002) 1257–1262, https://doi.org/10.1002/app.10457. [88] H. Wang, X. Sun, P. Seib, Effects of starch moisture on properties of wheat starch/ poly(lactic acid) blend containing methylenediphenyl diisocyanate, J. Polym. Environ. 10 (2002) 133–138, https://doi.org/10.1023/A:1021139903549. [89] T. Ke, X.S. Sun, Thermal and mechanical properties of poly(lactic acid)/starch/ methylenediphenyl diisocyanate blending with triethyl citrate, J. Appl. Polym. Sci. 88 (2003) 2947–2955, https://doi.org/10.1002/app.12112. [90] H. Wang, X. Sun, P. Seib, Properties of poly(lactic acid) blends with various starches as affected by physical aging, J. Appl. Polym. Sci. 90 (2003) 3683–3689, https://doi. org/10.1002/app.13001. [91] L. Yu, E. Petinakis, K. Dean, H. Liu, Q. Yuan, Enhancing compatibilizer function by controlled distribution in hydrophobic polylactic acid/hydrophilic starch blends, J. Appl. Polym. Sci. 119 (2010) 2189–2195, https://doi.org/10.1002/app.32949. [92] J.-F. Zhang, X. Sun, Mechanical properties of poly(lactic acid)/starch composites compatibilized by maleic anhydride, Biomacromolecules 5 (2004) 1446–1451, https://doi.org/10.1021/bm0400022. [93] J.-F. Zhang, X. Sun, Physical characterization of coupled poly(lactic acid)/starch/ maleic anhydride blends plasticized by acetyl triethyl citrate, Macromol. Biosci. 4 (2004) 1053–1060, https://doi.org/10.1002/mabi.200400076. [94] V.H. Orozco, W. Brostow, W. Chonkaew, B.L. López, Preparation and characterization of poly(lactic acid)-g-maleic anhydride starch blends, Macromol. Symp. 277 (2009) 69–80, https://doi.org/10.1002/masy.200950309. [95] C.-S. Wu, Improving polylactide/starch biocomposites by grafting polylactide with acrylic acid - characterization and biodegradability assessment, Macromol. Biosci. 5 (2005) 352–361, https://doi.org/10.1002/mabi.200400159. [96] E. Schwach, J.-L. Six, L. Avérous, Biodegradable blends based on starch and poly (lactic acid): comparison of different strategies and estimate of compatibilization, J. Polym. Environ. 16 (2008) 286–297, https://doi.org/10.1007/s10924-008-01076. [97] J. Liu, H. Jiang, L. Chen, Grafting of glycidyl methacrylate onto poly(lactide) and properties of PLA/starch blends compatibilized by the grafted copolymer, J. Polym. Environ. 20 (2012) 810–816, https://doi.org/10.1007/s10924-012-0438-1. [98] Z. Xiong, C. Li, S. Ma, J. Feng, Y. Yang, R. Zhang, et al., The properties of poly(lactic acid)/starch blends with a functionalized plant oil: Tung oil anhydride, Carbohydr. Polym. 95 (2013) 77–84, https://doi.org/10.1016/j.carbpol.2013.02.054. [99] Z. Xiong, L. Zhang, S. Ma, Y. Yang, C. Zhang, Z. Tang, et al., Effect of castor oil enrichment layer produced by reaction on the properties of PLA/HDI-g-starch blends, Carbohydr. Polym. 94 (2013) 235–243, https://doi.org/10.1016/j.carbpol.2013.01. 038. [100] S. Li, J. Xia, Y. Xu, X. Yang, W. Mao, K. Huang, Preparation and characterization of acorn starch/poly(lactic acid) composites modified with functionalized vegetable oil derivates, Carbohydr. Polym. 142 (2016) 250–258, https://doi.org/10.1016/j. carbpol.2016.01.031. [101] J. Zhang, X. Sun, Mechanical and thermal properties of poly (lactic acid)/starch blends with dioctyl maleate, J. Appl. Polym. Sci. 94 (2004) 1697–1704, https:// doi.org/10.1002/app.21078. [102] R. Gattin, A. Copinet, C. Bertrand, Y. Couturier, Biodegradation study of a starch and poly (lacticacid) co-extruded material in liquid, composting and inert mineral media, Int. Biodeterior. Biodegrad. 50 (2002) 25–31, https://doi.org/10.1016/ S0964-8305(02)00039-2. [103] G.H. Yew, A.M. Mohd Yusof, Z.A. Mohd Ishak, U.S. Ishiaku, Water absorption and enzymatic degradation of poly (lactic acid)/rice starch composites, Polym. Degrad. Stab. 90 (2005) 488–500, https://doi.org/10.1016/j.polymdegradstab.2005.04.006. [104] Y.F. Zuo, J. Gu, Z. Qiao, H. Tan, J. Cao, Y. Zhang, Effects of dry method esterification of starch on the degradation characteristics of starch/polylactic acid composites, Int. J. Biol. Macromol. 72 (2015) 391–402, https://doi.org/10.1016/j.ijbiomac.2014.08. 038. [105] R. Acioli-Moura, X.S. Sun, Thermal degradation and physical aging of poly(lactic acid) and its blends with starch, Polym. Eng. Sci. 48 (2008) 829–836, https://doi. org/10.1002/pen.21019. [106] T. Ohkita, S.-H. Lee, Thermal degradation and biodegradability of poly (lactic acid)/ corn starch biocomposites, J. Appl. Polym. Sci. 100 (2006) 3009–3017, https://doi. org/10.1002/app.23425. [107] S. Lv, J. Gu, J. Cao, H. Tan, Y. Zhang, Effect of annealing on the thermal properties of poly (lactic acid)/starch blends, Int. J. Biol. Macromol. 74 (2015) 297–303, https:// doi.org/10.1016/j.ijbiomac.2014.12.022.

348

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

[108] C. Réti, M. Casetta, S. Duquesne, S. Bourbigot, R. Delobel, Flammability properties of intumescent PLA including starch and lignin, Polym. Adv. Technol. 19 (2008) 628–635, https://doi.org/10.1002/pat.1130. [109] X. Wang, Y. Hu, L. Song, S. Xuan, W. Xing, Z. Bai, et al., Flame retardancy and thermal degradation of intumescent flame retardant poly(lactic acid)/starch biocomposites, Ind. Eng. Chem. Res. 50 (2011) 713–720, https://doi.org/10.1021/ ie1017157. [110] Z. Shen, Y. Zhou, J. Wang, Comparison of denitrification performance and microbial diversity using starch/polylactic acid blends and ethanol as electron donor for nitrate removal, Bioresour. Technol. 131 (2013) 33–39, https://doi.org/10.1016/j. biortech.2012.12.169. [111] S.W. Hwang, J.K. Shim, S. Selke, H. Soto-Valdez, L. Matuana, M. Rubino, et al., Migration of α-tocopherol and resveratrol from poly(L-lactic acid)/starch blends films into ethanol, J. Food Eng. 116 (2013) 814–828, https://doi.org/10.1016/j. jfoodeng.2013.01.032. [112] M. Sanyang, S. Sapuan, M. Jawaid, M. Ishak, J. Sahari, Development and characterization of sugar palm starch and poly(lactic acid) bilayer films, Carbohydr. Polym. 146 (2016) 36–45, https://doi.org/10.1016/j.carbpol.2016.03.051. [113] S. Zhang, X. Feng, S. Zhu, Q. Huan, K. Han, Y. Ma, et al., Novel toughening mechanism for polylactic acid (PLA)/starch blends with layer-like microstructure via pressure-induced flow (PIF) processing, Mater. Lett. 98 (2013) 238–241, https:// doi.org/10.1016/j.matlet.2012.12.019. [114] N.L. Bolay, A. Lamure, N.G. Leis, A. Subhani, How to combine a hydrophobic matrix and a hydrophilic filler without adding a compatibilizer – Co-grinding enhances use properties of renewable PLA–starch composites, Chem. Eng. Process. Process Intensif. 56 (2012) 1–9, https://doi.org/10.1016/j.cep.2012.03.005. [115] J. Wuk Park, S.S. Im, S.H. Kim, Y. Ha Kim, Biodegradable polymer blends of poly (Llactic acid) and gelatinized starch, Polym. Eng. Sci. 40 (2000) 2539–2550, https:// doi.org/10.1002/pen.11384. [116] B.Y. Shin, G.S. Jo, K.S. Kang, T.J. Lee, B.S. Kim, Morphology and rheology on the blends of PLA/CMPS, Macromol. Res. 15 (2007) 291–301, https://doi.org/10. 1007/BF03218790. [117] N. Chapleau, M.A. Huneault, H. Li, Biaxial orientation of polylactide/thermoplastic starch blends, Int. Polym. Process. 22 (2007) 412–418, https://doi.org/10.3139/ 217.2185. [118] M.A. Huneault, H. Li, Morphology and properties of compatibilized polylactide/ thermoplastic starch blends, Polymer 48 (2007) 270–280, https://doi.org/10. 1016/j.polymer.2006.11.023. [119] N. Wang, J. Yu, X. Ma, Preparation and characterization of thermoplastic starch/PLA blends by one-step reactive extrusion, Polym. Int. 56 (2007) 1440–1447, https:// doi.org/10.1002/pi.2302. [120] J. Ren, H. Fu, T. Ren, W. Yuan, Preparation, characterization and properties of binary and ternary blends with thermoplastic starch, poly(lactic acid) and poly(butylene adipate-co-terephthalate), Carbohydr. Polym. 77 (2009) 576–582. [121] J. Leadprathom, S. Suttiruengwong, P. Threepopnatkul, M. Seadan, Compatibilized polylactic acid/thermoplastic starch by reactive blend, J. Met. Mater. Miner. 20 (3) (2010) 87–90. [122] L. Yu, K. Dean, Q. Yuan, L. Chen, X. Zhang, Effect of compatibilizer distribution on the blends of starch/biodegradable polyesters, J. Appl. Polym. Sci. 103 (2007) 812–818, https://doi.org/10.1002/app.25184. [123] W. Ning, Y. Jiugao, M. Xiaofei, Preparation and characterization of compatible thermoplastic dry starch/poly (lactic acid), Polym. Compos. 29 (2008) 551–559, https://doi.org/10.1002/pc.20399. [124] N. Wang, J. Yu, P.R. Chang, X. Ma, Influence of formamide and water on the properties of thermoplastic starch/poly(lactic acid) blends, Carbohydr. Polym. 71 (2008) 109–118, https://doi.org/10.1016/j.carbpol.2007.05.025. [125] Y. Yang, Z. Tang, Z. Xiong, J. Zhu, Preparation and characterization of thermoplastic starches and their blends with poly (lactic acid), Int. J. Biol. Macromol. 77 (2015) 273–279, https://doi.org/10.1016/j.ijbiomac.2015.03.053. [126] M. Akrami, I. Ghasemi, H. Azizi, M. Karrabi, M. Seyedabadi, A new approach in compatibilization of the poly (lactic acid)/thermoplastic starch (PLA/TPS) blends, Carbohydr. Polym. 144 (2016) 254–262, https://doi.org/10.1016/j.carbpol.2016. 02.035. [127] H. Gao, S. Hu, F. Su, J. Zhang, G. Tang, Mechanical, thermal, and biodegradability properties of PLA/modified starch blends, Polym. Compos. 32 (2011) 2093–2100, https://doi.org/10.1002/pc.21241. [128] B.Y. Shin, S.H. Jang, B.S. Kim, Thermal, morphological, and mechanical properties of biobased and biodegradable blends of poly (lactic acid) and chemically modified thermoplastic starch, Polym. Eng. Sci. 51 (2011) 826–834, https://doi.org/10. 1002/pen.21896. [129] N. Wang, J. Yu, P.R. Chang, X. Ma, Influence of citric acid on the properties of glycerol-plasticized dry starch (DTPS) and DTPS/poly (lactic acid) blends, StarchStarke 59 (2007) 409–417, https://doi.org/10.1002/star.200700617. [130] J.M. Ferri, D. Garcia-Garcia, L. Sánchez-Nacher, O. Fenollar, R. Balart, The effect of maleinized linseed oil (MLO) on mechanical performance of poly (lactic acid)thermoplastic starch (PLA-TPS) blends, Carbohydr. Polym. 147 (2016) 60–68, https://doi.org/10.1016/j.carbpol.2016.03.082. [131] C. Yokesahachart, R. Yoksan, Effect of amphiphilic molecules on characteristics and tensile properties of thermoplastic starch and its blends with poly (lactic acid), Carbohydr. Polym. 83 (2011) 22–31, https://doi.org/10.1016/j.carbpol.2010.07. 020. [132] M.A. Shirai, C.M.O. Muller, M.V.E. Grossmann, F. Yamashita, Adipate and citrate esters as plasticizers for poly (lactic acid)/thermoplastic starch sheets, J. Polym. Environ. 23 (2015) 54–61, https://doi.org/10.1007/s10924-0140680-9.

[133] H. Li, M.A. Huneault, Comparison of sorbitol and glycerol as plasticizers for thermoplastic starch in TPS/PLA blends, J. Appl. Polym. Sci. 119 (2011) 2439–2448, https:// doi.org/10.1002/app.32956. [134] H. Li, M.A. Huneault, Effect of chain extension on the properties of PLA/TPS blends, J. Appl. Polym. Sci. 122 (2011) 134–141, https://doi.org/10.1002/app.33981. [135] J. Wootthikanokkhan, N. Wongta, N. Sombatsompop, A. Kositchaiyong, J. WongOn, S. Isarankurana Ayutthaya, N. Kaabbuathong, Effect of blending conditions on mechanical, thermal, and rheological properties of plasticized poly (lactic acid)/ maleated thermoplastic starch blends, J. Appl. Polym. Sci. 124 (2012) 1012–1019, https://doi.org/10.1002/app.35142. [136] W. Phetwarotai, P. Potiyaraj, D. Aht-Ong, Biodegradation of polylactide and gelatinized starch blend films under controlled soil burial conditions, J. Polym. Environ. 21 (1) (2013) 95–107, https://doi.org/10.1007/s10924-012-0530-6. [137] M. Thunga, K. Chen, D. Grewell, M.R. Kessler, Bio-renewable precursor fibers from lignin/polylactide blends for conversion to carbon fibers, Carbon 68 (2014) 159–166, https://doi.org/10.1016/j.carbon.2013.10.075. [138] S. Wang, Y. Li, H. Xiang, Z. Zhou, T. Chang, M. Zh, Low cost carbon fibers from biorenewable lignin/poly (lactic acid) (PLA) blends, Compos. Sci. Technol. 119 (2015) 20–25, https://doi.org/10.1016/j.compscitech.2015.09.021. [139] O. Gordobil, I. Egüés, R. Llano-Ponte, J. Labidi, Physicochemical properties of PLA lignin blends, Polym. Degrad. Stab. 108 (2014) 330–338, https://doi.org/10.1016/ j.polymdegradstab.2014.01.002. [140] O. Gordobil, R. Delucis, I. Egüés, R. Llano-Ponte, J. Labidi, Kraft lignin as filler in PLA to improve ductility and thermal properties, Ind. Crop. Prod. 72 (2015) 46–53, https://doi.org/10.1016/j.indcrop.2015.01.055. [141] M.A.S. Anwer, H.E. Naguib, A. Celzard, V. Fierro, Comparison of the thermal, dynamic mechanical and morphological properties of PLA-Lignin & PLA-Tannin particulate green composites, Compos. Part B 82 (2015) 92–99, https://doi.org/10. 1016/j.compositesb.2015.08.028. [142] I. Spiridon, K. Leluk, A.M. Resmerita, R.N. Darie, Evaluation of PLA–lignin bioplastics properties before and after accelerated weathering, Compos. Part B 69 (2015) 342–349. [143] R.K. Singla, S.N. Maiti, A.K. Ghosh, Crystallization, morphological, and mechanical response of poly (lactic acid)/lignin-based biodegradable composites, polymerplastics, Technol. Eng. 55 (2016) 475–485, https://doi.org/10.1080/03602559. 2015.1098688. [144] S. Kim, S. Oh, J. Lee, N. Ahn, H. Roh, J. Cho, B. Chun, J. Park, Effect of alkyl-chainmodified lignin in the PLA matrix, Fibers Polym. 15 (2014) 2458–2465, https:// doi.org/10.1007/s12221-014-2458-z. [145] E. Bugnicourt, P. Cinelli, A. Lazzeri, V. Alvarez, Polyhydroxyalkanoate (PHA): review of synthesis, characteristics, processing and potential applications in packaging, Express Polym Lett 8 (2014) 791–808, https://doi.org/10.3144//expresspolymlett. 2014.82. [146] Q. Zhao, S. Wang, M. Kong, W. Geng, R.K. Li, C. Song, D. Kong, Phase morphology, physical properties, and biodegradation behavior of novel PLA/PHBHHx blends, J Biomed Mater Res B Appl Biomater 100 (2012) 23–31, https://doi.org/10.1002/ jbm.b.31915. [147] M.A. Abdelwahab, A. Flynn, B. Chiou, S. Imam, W. Orts, E. Chiellini, Thermal, mechanical and morphological characterization of plasticized PLA/PHB blends, Polym. Degrad. Stab. 97 (2012) 1822–1828, https://doi.org/10.1016/j. polymdegradstab.2012.05.036. [148] B.M.P. Ferreira, C.A.C. Zavaglia, E.A.R. Duek, Films of PLLA/PHBV: thermal, morphological, and mechanical characterization, J. Appl. Polym. Sci. 86 (2002) 2898–2906, https://doi.org/10.1002/app.11334. [149] E. Richards, R. Rizvi, A. Chow, H. Naguib, Biodegradable composite foams of PLA and PHBV using subcritical CO2, J. Polym. Environ. 16 (2008) 258–266. [150] E. Blümm, A.J. Owen, Miscibility, crystallization, and melting of poly(3hydroxybutyrate)/poly(L-lactide blends), Polymer 36 (1995) 4077–4081, https:// doi.org/10.1016/0032-3861(95)90987-D. [151] N. Koyama, Y. Doi, Miscibility of binary blends of poly[(R)-3-ydroxybutyric acid] and poly[(S)-Iactic acid], Polymer 38 (1997) 1589–1593, https://doi.org/10.1016/ S0032-3861(96)00685-4. [152] J. Zhang, H. Sato, T. Furukawa, H. Tsuji, I. Noda, Y. Ozaki, Crystallization behaviors of poly(3-hydroxybutyrate) and poly(L-lactic acid) in their immiscible and miscible blends, J. Phys. Chem. 110 (2006) 24463–24471, https://doi.org/10.1021/ jp065233c. [153] I. Ohkoshia, H. Abeb, Y. Doi, Miscibility and solid-state structures for blends of poly [(S)-lactide] with atactic poly[(R,S)-3-hydroxybutyrate], Polymer 41 (2000) 5985–5992, https://doi.org/10.1016/S0032-3861(99)00781-8. [154] L. Zhang, C. Xiong, X. Deng, Miscibility, crystallization, and morphology of poly(βhydroxybutyrate)/poly(D,L-lactide) blends, Polymer 37 (1996) 235–241, https:// doi.org/10.1016/0032-3861(96)81093-7. [155] Y. Kikkawa, T. Suzuki, T. Tsuge, M. Kanesato, Y. Doi, H. Abe, Phase structure and enzymatic degradation of poly(L-lactide)/atactic poly(3-hydroxybutyrate) blends: an atomic force microscopy study, Biomacromolecules 7 (2006) 1921–1928, https:// doi.org/10.1021/bm0600163. [156] Y. Kikkawa, T. Suzuki, T. Tsuge, M. Kanesato, Y. Doi, H. Abe, Effect of phase structure on enzymatic degradation in poly(L-lactide)/atactic poly(3-hydroxybutyrate) blends with different miscibility, Biomacromolecules 10 (2009) 1013–1018, https://doi.org/10.1021/bm900117J. [157] A.P. Bonartsev, A.P. Boskhomodgiev, A.L. Iordanskii, G.A. Bonartseva, A.V. Rebrov, T.K. Makhina, V.L. Myshkina, S.A. Yakovlev, E.A. Filatova, E.A. Ivanov, D.V. Bagrov, G.E. Zaikov, Hydrolytic degradation of poly(3-hydroxybutyrate), polylactide and their derivatives: kinetics, crystallinity, and surface morphology, Mol. Cryst. Liq. Cryst. 556 (2012) 288–300, https://doi.org/10.1080/ 15421406.2012.635982.

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360 [158] M. Zhang, N.L. Thomas, Blending polylactic acid with polyhydroxybutyrate: the effect on thermal, mechanical, and biodegradation properties, Adv. Polym. Technol. 30 (2011) 67–79, https://doi.org/10.1002/adv.20235. [159] Z. Bartczak, A. Galeski, M. Kowalczuk, M. Sobota, R. Malinowski, Tough blends of poly(lactide) and amorphous poly([R,S]-3-hydroxy butyrate)–morphology and properties, Eur. Polym. J. 49 (2013) 3630–3641, https://doi.org/10.1016/j. eurpolymj.2013.07.033. [160] M. Musioł, W. Sikorska, G. Adamus, H. Janeczek, M. Kowalczuk, J. Rydz, (Bio)degradable polymers as a potential material for food packaging: studies on the (bio)degradation process of PLA/(R,S)-PHB rigid foils under industrial composting conditions, Eur. Food Res. Technol. 242 (2016) 815–823. [161] W. Dong, P. Ma, S. Wang, M. Chen, X. Cai, Y. Zhang, Effect of partial crosslinking on morphology and properties of the poly(b-hydroxybutyrate)/poly(D,L-lactic acid) blends, Polym. Degrad. Stab. 98 (2013) 1549–1555, https://doi.org/10.1016/j. polymdegradstab.2013.06.033. [162] I. Armentano, E. Fortunati, N. Burgos, F. Dominici, F. Luzi, S. Fiori, A. Jimenez, K. Yoon, j. Ahn, S. Kang, J.M. Kenny, Processing and characterization of plasticized PLA/PHB blends for biodegradable multiphase systems, Express Polym Lett 9 (2015) 583–596, https://doi.org/10.3144/expresspolymlett.2015.55. [163] I. Armentano, E. Fortunati, N. Burgos, F. Dominici, F. Luzi, S. Fiori, et al., Processing and characterization of plasticized PLA/PHB blends for biodegradable multiphase systems, Express Polym Lett 9 (2015) 583–596, https://doi.org/10.3144/ expresspolymlett.2015.55. [164] M.P. Arrieta, J. López, A. Hernández, E. Rayón, Ternary PLA–PHB–Limonene blends intended for biodegradable food packaging applications, Eur. Polym. J. 50 (2014) 255–270, https://doi.org/10.1016/j.eurpolymj.2013.11.009. [165] M.P. Arrieta, J. López, E. Rayón, A. Jimenez, Disintegrability under composting conditions of plasticized PLA/PHB blends, Polym. Degrad. Stab. 108 (2014) 307–318, https://doi.org/10.1016/j.polymdegradstab.2014.01.034. [166] M.P. Arrieta, M.M. Castro-Loṕez, E. Rayón, L.F. Barral-Losada, J.M. LoṕezVilariño, J. López, M.V. Gonzaĺez-Rodríguez, Plasticized poly(lactic acid) −poly(hydroxybutyrate) (PLA−PHB) blends incorporated with catechin intended for active food-packaging applications, J. Agric. Food Chem. 62 (2014) 10170–10250, https://doi.org/10.1021/jf5029812. [167] M.P. Arrieta, J. López, J.M. Kenny, L. Peponi, Development of flexible materials based on plasticized electrospun PLA–PHB blends: structural, thermal, mechanical and disintegration properties, Eur. Polym. J. 73 (2015) 433–446, https://doi.org/10. 1016/j.eurpolymj.2015.10.036. [168] A. Nicosia, W. Gieparda, J. Foksowicz-Flaczyk, J. Walentowska, D. Wesołek, B. Vazquez, F. Prodi, F. Belosi, Air filtration and antimicrobial capabilities of electrospun PLA/PHB containing ionic liquid, Sep. Purif. Technol. 154 (2015) 154–160, https://doi.org/10.1016/j.seppur.2015.09.037. [169] L. Han, C. Han, H. Zhang, S. Chen, L. Dong, Morphology and properties of biodegradable and biosourced polylactide blends with poly(3-hydroxybutyrate-co-4hydroxybutyrate), Polym. Compos. 33 (2012) 850–859, https://doi.org/10.1002/ pc.22213. [170] Y. Weng, L. Wang, M. Zhang, X. Wang, Y. Wang, Biodegradation behavior of P (3HB,4HB)/PLA blends in real soil environments, Polym. Test. 32 (2013) 60–70, https://doi.org/10.1016/j.polymertesting.2012.09.014. [171] H. Li, X. Lu, H. Yang, J. Hu, Non-isothermal crystallization of P(3HB-co-4HB)/PLA blends crystallization kinetic, melting behavior and crystal morphology, J. Therm. Anal. Calorim. 122 (2015) 817–829, https://doi.org/10.1007/s10973-015-4824-5. [172] S. Iannace, L. Ambrosio, S.J. Huang, L. Nicolais, Poly(3-hydroxybutyrate)-co-(3hydroxyvalerate)/poly-L-lactide blends: thermal and mechanical properties, J. Appl. Polym. Sci. 54 (1994) 1525–1535, https://doi.org/10.1002/app.1994. 070541017. [173] S. Iannace, L. Ambrosio, S.J. Huang, L. Nicolais, Effect of degradation on the mechanical properties of multiphase polymer blends: PHBV/PLLA, J. Macromol. Sci. A 32 (1995) 881–888, https://doi.org/10.1080/10601329508010301. [174] I. Zembouai, S. Bruzaud, M. Kaci, A. Benhamida, Y. Corre, Y. Grohens, A. Taguet, J. Lopez-Cuesta, Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/polylactide blends: thermal stability, flammability and thermo-mechanical behavior, J. Polym. Environ. 22 (2014) 131–139, https://doi.org/10.1007/s10924-013-0626-7. [175] Q. Liu, C. Wu, H. Zhang, B. Deng, Blends of polylactide and poly(3hydroxybutyrate-co-3-hydroxyvalerate) with low content of hydroxyvalerate unit: morphology, structure, and property, J. Appl. Polym. Sci. 132 (2015) 42689–42698, https://doi.org/10.1002/app.42689. [176] M.R. Nanda, M. Misra, A.K. Mohanty, The Effects of Process Engineering on the Performance of PLA and PHBV Blends, Macromol. Mater. Eng. 296 (2011) 719–728, https://doi.org/10.1002/mame.201000417. [177] T. Gerard, T. Budtova, Morphology and molten-state rheology of polylactide and polyhydroxyalkanoate blends, Eur. Polym. J. 48 (2012) 1110–1117, https://doi. org/10.1016/j.eurpolymj.2012.03.015. [178] S. Modi, K. Koelling, Y. Vodovotz, Miscibility of poly(3-hydroxybutyrate-co-3hydroxyvalerate) with high molecular weight poly(lactic acid) blends determined by thermal analysis, J. Appl. Polym. Sci. 124 (2012) 3074–3081, https://doi.org/10. 1002/app.35343. [179] M. Boufarguine, A. Guinault, G. Miquelard-Garnier, C. Sollogoub, PLA/PHBV films with improved mechanical and gas barrier properties, Macromol. Mater. Eng. 298 (2013) 1065–1073, https://doi.org/10.1002/mame.201200285. [180] P. Ma, A.B. Spoelstra, P. Schmit, P.J. Lemstra, Toughening of poly (lactic acid) by poly (b-hydroxybutyrate-co-b-hydroxyvalerate) with high b-hydroxyvalerate content, Eur. Polym. J. 49 (2013) 1523–1531, https://doi.org/10.1016/j. eurpolymj.2013.01.016. [181] I. Zembouai, M. Kaci, S. Bruzaud, A. Benhamida, Y. Corre, Y. Grohens, A study of morphological, thermal, rheological and barrier properties of Poly(3-

[182]

[183]

[184]

[185]

[186]

[187]

[188]

[189]

[190]

[191]

[192]

[193]

[194]

[195]

[196]

[197]

[198]

[199]

[200]

[201]

[202]

[203]

[204]

[205]

349

hydroxybutyrate-Co-3-Hydroxyvalerate)/polylactide blends prepared by melt mixing, Polym. Test. 32 (2013) 842–851, https://doi.org/10.1016/j. polymertesting.2013.04.004. J. Yang, H. Zhu, C. Zhang, Q. Jiang, Y. Zhao, P. Chen, D. Wang, Transesterification induced mechanical properties enhancement of PLLA/PHBV bio-alloy, Polymer 83 (2016) 230–238, https://doi.org/10.1016/j.polymer.2015.12.025. J. Gonzalez-Ausejo, E. Sanchez-Safont, J.M. Lagaron, R.T. Olsson, J. Gamez-Perez, L. Cabedo, Assessing the thermoformability of poly (3-hydroxybutyrate-co-3hydroxyvalerate)/poly (acid lactic) blends compatibilized with diisocyanates, Polym. Test. 62 (2017) 235–245. J. Gonzalez-Ausejo, E. Sanchez-Safont, J.M. Lagaron, R.T. Olsson, J. Gamez-Perez, L. Cabedo, Assessing the thermoformability of poly (3-hydroxybutyrate-co-3hydroxyvalerate)/poly (acid lactic) blends compatibilized with diisocyanates, Polym. Test. 62 (2017) 235–245, https://doi.org/10.1016/j.polymertesting.2017. 06.026. J. Gonzalez-Ausejo, E. Sanchez-Safont, J.M. Lagaron, R. Balart, L. Cabedo, J. GamezPerez, Compatibilization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)–poly (lactic acid) blends with diisocyanates, J. Appl. Polym. Sci. 134 (2017)https://doi. org/10.1002/APP.44806. T. Qiang, J. Wang, M.P. Wolcott, Facile fabrication of 100% bio-based and degradable ternary cellulose/PHBV/PLA composite, Materials 11 (2018) 330, https://doi. org/10.3390/ma11020330. Y. He, Z. Hu, M. Ren, C. Ding, P. Chen, Q. Gu, Q. Wu, Evaluation of PHBHHx and PHBV/PLA fibers used as medical sutures, J. Mater. Sci. Mater. Med. 25 (2014) 561–571, https://doi.org/10.1007/s10856-013-5073-4. H.C. Chang, T. Sun, N. Sultana, M.M. Lim, T.H. Khan, A.F. Ismail, Conductive PEDOT: PSS coated polylactide (PLA) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) electrospun membranes: fabrication and characterization, Mater. Sci. Eng. C 61 (2016) 396–410, https://doi.org/10.1016/j.msec.2015.12.074. A. Wagner, V. Poursorkhabi, A.K. Mohanty, M. Misra, Analysis of porous electrospun fibers from poly(L-lactic acid)/poly(3-hydroxybutyrate-co-3hydroxyvalerate) blends, ACS Sustain. Chem. Eng. 2 (2014) 1976–1982, https:// doi.org/10.1021/sc5000495. L. Li, W. Huang, B. Wang, W. Wei, Q. Gu, P. Chen, Properties and structure of polylactide/poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PLA/PHBV) blend fibers, Polymer 68 (2015) 183–194, https://doi.org/10.1016/j.polymer.2015.05.024. R.M. Rasal, D.E. Hirt, Toughness decrease of PLA-PHBHHx blend films upon surfaceconfined photopolymerization, J. Biomed. Mater. Res. A 88 (2009) 1079–1086, https://doi.org/10.1002/jbm.a.32009. M.A. Woodruff, D.W. Hutmacher, The return of a forgotten polymer— polycaprolactone in the 21st century, Prog. Polym. Sci. 35 (2010) 1217–1256, https://doi.org/10.1016/j.progpolymsci.2010.04.002. H. Kweon, M.K. Yoo, I.K. Park, T.H. Kim, H.C. Lee, H. Lee, J. Oh, T. Akaike, C. Cho, A novel degradable polycaprolactone networks for tissue engineering, Biomaterials 24 (2003) 801–808, https://doi.org/10.1016/s0142-9612(02)00370-8. H. Tsuji, Y. Ikada, Blends of aliphatic polyesters. I. Physical properties and morphologies of solution-cast blends from poly(DL-lactide) and poly(E-caprolactone), J. Appl. Polym. Sci. 60 (1996) 2367–2375, https://doi.org/10.1002/(sici)1097-4628 (19960627)60:13b2367::aid-app8N3.0.co;2-c. H. Tsuji, Y. Ikada, Blends of aliphatic polyesters. II. Hydrolysis of solution-cast blends from poly(L-lactide) and poly(Ε-caprolactone) in phosphate-buffered solution, J. Appl. Polym. Sci. 67 (1998) 405–415, https://doi.org/10.1002/(sici)10974628(19980118)67:3b405::aid-app3N3.3.co;2-n. K. Fukushima, J.L. Feijoo, M.-C. Yang, Comparison of abiotic and biotic degradation of PDLLA, PCL and partially miscible PDLLA/PCL blend, Eur. Polym. J. 49 (2013) 706–717, https://doi.org/10.1016/j.eurpolymj.2012.12.011. L. Liu, S. Li, H. Garreau, M. Vert, Selective enzymatic degradations of poly(l-lactide) and poly(ε-caprolactone) blend films, Biomacromolecules 1 (2000) 350–359, https://doi.org/10.1021/bm000046k. Q. Cai, J. Bei, S. Wang, In vitro study on the drug release behavior from polylactidebased blend matrices, Polym. Adv. Technol. 13 (2002) 534–540, https://doi.org/10. 1002/pat.222. S. Li, L. Liu, H. Garreau, M. Vert, Lipase-catalyzed biodegradation of poly(εcaprolactone) blended with various polylactide-based polymers, Biomacromolecules 4 (2003) 372–377, https://doi.org/10.1021/ bm025748j. G. Sivalingam, S.P. Vijayalakshmi, G. Madras, Enzymatic and thermal degradation of poly(ε-caprolactone), poly(d,l-lactide), and their blends, Ind. Eng. Chem. Res. 43 (2004) 7702–7709, https://doi.org/10.1021/ie049589r. G. Sivalingam, Thermal degradation of binary physical mixtures and copolymers of poly(3-caprolactone), poly(D,L-lactide), poly(glycolide), Polym. Degrad. Stab. 84 (2004) 393–398, https://doi.org/10.1016/s0141-3910(03)00411-7. L.A. Gaona, J.G. Ribelles, J.E. Perilla, M. Lebourg, Hydrolytic degradation of PLLA/PCL microporous membranes prepared by freeze extraction, Polym. Degrad. Stab. 97 (2012) 1621–1632, https://doi.org/10.1016/j. polymdegradstab.2012.06.031. A. Vieira, J. Vieira, J. Ferra, F. Magalhães, R. Guedes, A. Marques, Mechanical study of PLA–PCL fibers during in vitro degradation, J. Mech. Behav. Med. Mater. 4 (2011) 451–460, https://doi.org/10.1016/j.jmbbm.2010.12.006. C.-H. Kim, K.Y. Cho, E.-J. Choi, J.-K. Park, Effect of P(lLA-co-?CL) on the compatibility and crystallization behavior of PCL/PLLA blends, J. Appl. Polym. Sci. 77 (2000) 226–231, https://doi.org/10.1002/(sici)1097-4628(20000705)77:1b226::aidapp29N3.0.co;2-8. M. Todo, S.-D. Park, T. Takayama, K. Arakawa, Fracture micromechanisms of bioabsorbable PLLA/PCL polymer blends, Eng. Fract. Mech. 74 (2007) 1872–1883, https://doi.org/10.1016/j.engfracmech.2006.05.021.

350

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

[206] C.L. Simões, J.C. Viana, A.M. Cunha, Mechanical properties of poly(ε-caprolactone) and poly(lactic acid) blends, J. Appl. Polym. Sci. 112 (2009) 345–352, https://doi. org/10.1002/app.29425. [207] N. Noroozi, L.L. Schafer, S.G. Hatzikiriakos, Thermorheological properties of poly (εcaprolactone)/polylactide blends, Polym. Eng. Sci. 52 (2012) 2348–2359, https:// doi.org/10.1002/pen.23186. [208] F. Sakai, K. Nishikawa, Y. Inoue, K. Yazawa, Nucleation enhancement effect in poly (L-lactide) (PLLA)/poly(ϵ-caprolactone) (PCL) blend induced by locally activated chain mobility resulting from limited miscibility, Macromolecules 42 (2009) 8335–8342, https://doi.org/10.1021/ma901547a. [209] F. Cock, A. Cuadri, M. García-Morales, P. Partal, Thermal, rheological and microstructural characterisation of commercial biodegradable polyesters, Polym. Test. 32 (2013) 716–723, https://doi.org/10.1016/j.polymertesting.2013.03.015. [210] O.J. Botlhoko, J. Ramontja, S.S. Ray, A new insight into morphological, thermal, and mechanical properties of melt-processed polylactide/poly(εcaprolactone) blends, Polym. Degrad. Stab. 154 (2018) 84–95, https://doi. org/10.1016/j.polymdegradstab.2018.05.025. [211] D. Newman, E. Laredo, A. Bello, Grillo Angélica, Feijoo José Luis, J. Müller Alejandro, Molecular mobilities in biodegradable poly(DL-lactide)/poly(ε-caprolactone) blends, Macromolecules 42 (2009) 5219–5225, https://doi.org/10.1021/ ma9007303. [212] C.-C. Chen, J.-Y. Chueh, H. Tseng, H.-M. Huang, S.-Y. Lee, Preparation and characterization of biodegradable PLA polymeric blends, Biomaterials 24 (2003) 1167–1173, https://doi.org/10.1016/s0142-9612(02)00466-0. [213] N. López-Rodríguez, A. López-Arraiza, E. Meaurio, J. Sarasua, Crystallization, morphology, and mechanical behavior of polylactide/poly(ɛ-caprolactone) blends, Polym. Eng. Sci. 46 (2006) 1299–1308, https://doi.org/10.1002/pen.20609. [214] J. Urquijo, G. Guerrica-Echevarría, J.I. Eguiazábal, Melt processed PLA/PCL blends: effect of processing method on phase structure, morphology, and mechanical properties, J. Appl. Polym. Sci. 132 (2015)https://doi.org/10.1002/app.42641. [215] Y.-H. Na, Y. He, X. Shuai, Y. Kikkawa, Y. Doi, Y. Inoue, Compatibilization effect of poly(ε-caprolactone)-b-poly(ethylene glycol) block copolymers and phase morphology analysis in immiscible poly(lactide)/poly(ε-caprolactone) blends, Biomacromolecules 3 (2002) 1179–1186, https://doi.org/10.1021/bm020050r. [216] V. Vilay, M. Mariatti, Z. Ahmad, K. Pasomsouk, M. Todo, Improvement of microstructures and properties of biodegradable PLLA and PCL blends compatibilized with a triblock copolymer, Mater. Sci. Eng. A 527 (2010) 6930–6937, https://doi. org/10.1016/j.msea.2010.07.079. [217] L. Gardella, M. Calabrese, O. Monticelli, PLA maleation: an easy and effective method to modify the properties of PLA/PCL immiscible blends, Colloid Polym. Sci. 292 (2014) 2391–2398, https://doi.org/10.1007/s00396-014-3328-3. [218] M. Harada, K. Iida, K. Okamoto, H. Hayashi, K. Hirano, Reactive compatibilization of biodegradable poly(lactic acid)/poly(ɛ-caprolactone) blends with reactive processing agents, Polym. Eng. Sci. 48 (2008) 1359–1368, https://doi.org/10.1002/pen. 21088. [219] F. Tuba, L. Oláh, P. Nagy, Characterization of reactively compatibilized poly(d,llactide)/poly(ε-caprolactone) biodegradable blends by essential work of fracture method, Eng. Fract. Mech. 78 (2011) 3123–3133, https://doi.org/10.1016/j. engfracmech.2011.09.010. [220] T. Takayama, M. Todo, Improvement of impact fracture properties of PLA/PCL polymer blend due to LTI addition, J. Mater. Sci. 41 (2006) 4989–4992, https://doi.org/ 10.1007/s10853-006-0137-1. [221] L. Wang, W. Ma, R. Gross, S. Mccarthy, Reactive compatibilization of biodegradable blends of poly(lactic acid) and poly(ε-caprolactone), Polym. Degrad. Stab. 59 (1998) 161–168, https://doi.org/10.1016/s0141-3910(97)00196-1. [222] T. Semba, K. Kitagawa, U.S. Ishiaku, H. Hamada, The effect of crosslinking on the mechanical properties of polylactic acid/polycaprolactone blends, J. Appl. Polym. Sci. 101 (2006) 1816–1825, https://doi.org/10.1002/app.23589. [223] H. Bai, H. Xiu, J. Gao, H. Deng, Q. Zhang, M. Yang, et al., Tailoring impact toughness of poly(L-lactide)/poly(ε-caprolactone) (PLLA/PCL) blends by controlling crystallization of PLLA matrix, Appl. Mater. Interfaces 4 (2012) 897–905, https://doi.org/10. 1021/am201564f. [224] B.Y. Shin, D.H. Han, Compatibilization of immiscible poly(lactic acid)/poly(εcaprolactone) blend through electron-beam irradiation with the addition of a compatibilizing agent, Radiat. Phys. Chem. 83 (2013) 98–104, https://doi.org/10. 1016/j.radphyschem.2012.10.001. [225] O. Monticelli, M. Calabrese, L. Gardella, A. Fina, E. Gioffredi, Silsesquioxanes: novel compatibilizing agents for tuning the microstructure and properties of PLA/PCL immiscible blends, Eur. Polym. J. 58 (2014) 69–78, https://doi.org/10.1016/j. eurpolymj.2014.06.021. [226] E.A.J. Al-Mulla, N.A.B. Ibrahim, K. Shameli, M.B. Ahmad, W.M.Z.W. Yunus, Effect of epoxidized palm oil on the mechanical and morphological properties of a PLA– PCL blend, Res. Chem. Intermed. 40 (2013) 689–698, https://doi.org/10.1007/ s11164-012-0994-y. [227] D. Wu, Y. Zhang, M. Zhang, W. Zhou, Phase behavior and its viscoelastic response of polylactide/poly(ε-caprolactone) blend, Eur. Polym. J. 44 (2008) 2171–2183, https://doi.org/10.1016/j.eurpolymj.2008.04.023. [228] J.F. Palierne, Linear rheology of viscoelastic emulsions with interfacial tension, Rheol. Acta 29 (1990) 204–214, https://doi.org/10.1007/bf01331356. [229] Y. Zhang, D. Wu, M. Zhang, W. Zhou, C. Xu, Effect of steady shear on the morphology of biodegradable poly(ϵ-caprolactone)/polylactide blend, Polym. Eng. Sci. 49 (2009) 2293–2300, https://doi.org/10.1002/pen.21456. [230] S. Aslan, L. Calandrelli, P. Laurienzo, M. Malinconico, C. Migliaresi, Poly(D,L-lactic acid)/poly (ε-caprolactone) blend membranes: preparation and morphological characterization, J. Mater. Sci. 35 (2000) 1615–1622, https://doi.org/10.1023/A: 1004787326273.

[231] L. Calandrelli, A. Calarco, P. Laurienzo, M. Malinconico, O. Petillo, G. Peluso, Compatibilized polymer blends based on PDLLA and PCL for application in bioartificial liver, Biomacromolecules 9 (2008) 1527–1534, https://doi.org/10. 1021/bm7013087. [232] M. Lebourg, J.S. Antón, J.G. Ribelles, Porous membranes of PLLA–PCL blend for tissue engineering applications, Eur. Polym. J. 44 (2008) 2207–2218, https://doi. org/10.1016/j.eurpolymj.2008.04.033. [233] M. Sun, P.J. Kingham, A.J. Reid, S.J. Armstrong, G. Terenghi, S. Downes, In vitroandin vivotesting of novel ultrathin PCL and PCL/PLA blend films as peripheral nerve conduit, J. Biomed. Mater. Res. A 9999A (2009)https://doi.org/10.1002/jbm. a.32681. [234] E. Huang, X. Liao, Y. He, B. He, Q. Yang, G. Li, A novel route to the generation of porous scaffold based on the phase morphology control of co-continuous poly(εcaprolactone)/polylactide blend in supercritical CO2, Polymer 118 (2017) 163–172, https://doi.org/10.1016/j.polymer.2017.04.065. [235] S. Jain, M.M. Reddy, A.K. Mohanty, M. Misra, A.K. Ghosh, A new biodegradable flexible composite sheet from poly(lactic acid)/poly(ε-caprolactone) blends and micro-talc, Macromol. Mater. Eng. 295 (2010) 750–762, https://doi.org/10.1002/ mame.201000063. [236] L. Peponi, V. Sessini, M.P. Arrieta, I. Navarro-Baena, A. Sonseca, D. Dominici, E. Gimenez, L. Torre, A. Tercjak, D. Lopez, Thermally-activated shape memory effect on biodegradable nanocomposites based on PLA/PCL blend reinforced with hydroxyapatite, Polym. Degrad. Stab. 151 (2018) 36–51. [237] L. Jiang, M.P. Wolcott, J. Zhang, Study of biodegradable polylactide/poly(butylene adipate-co-terephthalate) blends, Biomacromolecules 7 (2006) 199–207, https:// doi.org/10.1021/bm050581q. [238] M. Nofar, A. Tabatabaei, H. Sojoudiasli, C. Park, P. Carreau, M.-C. Heuzey, et al., Mechanical and bead foaming behavior of PLA-PBAT and PLA-PBSA blends with different morphologies, Eur. Polym. J. 90 (2017) 231–244, https://doi.org/10.1016/j. eurpolymj.2017.03.031. [239] Y. Deng, C. Yu, P. Wongwiwattana, N.L. Thomas, Optimising ductility of poly(lactic acid)/poly(butylene adipate-co-terephthalate) blends through co-continuous phase morphology, J. Polym. Environ. 26 (2018) 3802–3816, https://doi.org/10. 1007/s10924-018-1256-x. [240] S. Lee, Y. Lee, J.W. Lee, Effect of ultrasound on the properties of biodegradable polymer blends of poly(lactic acid) with poly(butylene adipate-co-terephthalate), Macromol. Res. 15 (2007) 44–50, https://doi.org/10.1007/bf03218751. [241] M.-B. Coltelli, I.D. Maggiore, M. Bertoldo, F. Signori, S. Bronco, F. Ciardelli, Poly(lactic acid) properties as a consequence of poly(butylene adipate-co-terephthalate) blending and acetyl tributyl citrate plasticization, J. Appl. Polym. Sci. 110 (2008) 1250–1262, https://doi.org/10.1002/app.28512. [242] R. Al-Itry, K. Lamnawar, A. Maazouz, Improvement of thermal stability, rheological and mechanical properties of PLA, PBAT and their blends by reactive extrusion with functionalized epoxy, Polym. Degrad. Stab. 97 (2012) 1898–1914, https:// doi.org/10.1016/j.polymdegradstab.2012.06.028. [243] R. Al-Itry, K. Lamnawar, A. Maazouz, Reactive extrusion of PLA, PBAT with a multifunctional epoxide: physico-chemical and rheological properties, Eur. Polym. J. 58 (2014) 90–102, https://doi.org/10.1016/j.eurpolymj.2014.06.013. [244] R. Al-Itry, K. Lamnawar, A. Maazouz, N. Billon, C. Combeaud, Effect of the simultaneous biaxial stretching on the structural and mechanical properties of PLA, PBAT and their blends at rubbery state, Eur. Polym. J. 68 (2015) 288–301, https://doi.org/ 10.1016/j.eurpolymj.2015.05.001. [245] L.C. Arruda, M. Magaton, R.E.S. Bretas, M.M. Ueki, Influence of chain extender on mechanical, thermal and morphological properties of blown films of PLA/PBAT blends, Polym. Test. 43 (2015) 27–37, https://doi.org/10.1016/j.polymertesting. 2015.02.005. [246] W. Dong, B. Zou, Y. Yan, P. Ma, M. Chen, Effect of chain-extenders on the properties and hydrolytic degradation behavior of the poly(lactide)/poly(butylene adipateco-terephthalate) blends, Int. J. Mol. Sci. 14 (2013) 20189–20203, https://doi.org/ 10.3390/ijms141020189. [247] W. Dong, B. Zou, P. Ma, W. Liu, X. Zhou, D. Shi, et al., Influence of phthalic anhydride and bioxazoline on the mechanical and morphological properties of biodegradable poly(lactic acid)/poly[(butylene adipate)-co-terephthalate] blends, Polym. Int. 62 (2013) 1783–1790, https://doi.org/10.1002/pi.4568. [248] N. Zhang, Q. Wang, J. Ren, L. Wang, Preparation and properties of biodegradable poly(lactic acid)/poly(butylene adipate-co-terephthalate) blend with glycidyl methacrylate as reactive processing agent, J. Mater. Sci. 44 (2008) 250–256, https://doi.org/10.1007/s10853-008-3049-4. [249] M. Nishida, H. Ichihara, H. Watanabe, N. Fukuda, H. Ito, Improvement of dynamic tensile properties of poly(lactic acid)/poly(butylene adipate-co-terephthalate) polymer alloys using a crosslinking agent and observation of fracture surfaces, Int. J. Impact Eng. 79 (2015) 117–125, https://doi.org/10.1016/j.ijimpeng.2014. 11.010. [250] M.-B. Coltelli, S. Bronco, C. Chinea, The effect of free radical reactions on structure and properties of poly(lactic acid) (PLA) based blends, Polym. Degrad. Stab. 95 (2010) 332–341, https://doi.org/10.1016/j.polymdegradstab.2009. 11.015. [251] N. Zhang, C. Zeng, L. Wang, J. Ren, Preparation and properties of biodegradable poly (lactic acid)/poly(butylene adipate-co-terephthalate) blend with epoxy-functional styrene acrylic copolymer as reactive agent, J. Polym. Environ. 21 (2012) 286–292, https://doi.org/10.1007/s10924-012-0448-z. [252] P. Ma, X. Cai, Y. Zhang, S. Wang, W. Dong, M. Chen, et al., In-situ compatibilization of poly(lactic acid) and poly(butylene adipate-co-terephthalate) blends by using dicumyl peroxide as a free-radical initiator, Polym. Degrad. Stab. 102 (2014) 145–151, https://doi.org/10.1016/j. polymdegradstab.2014.01.025.

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360 [253] K. Sirisinha, W. Somboon, Melt characteristics, mechanical, and thermal properties of blown film from modified blends of poly(butylene adipate-co-terephthalate) and poly(lactide), J. Appl. Polym. Sci. (2011)https://doi.org/10.1002/app.35604. [254] L.C. Lins, S. Livi, J. Duchet-Rumeau, J.-F. Gérard, Phosphonium ionic liquids as new compatibilizing agents of biopolymer blends composed of poly(butylene-adipateco-terephtalate)/poly(lactic acid) (PBAT/PLA), RSC Adv. 5 (2015) 59082–59092, https://doi.org/10.1039/c5ra10241c. [255] N. Wu, H. Zhang, Mechanical properties and phase morphology of super-tough PLA/PBAT/EMA-GMA multicomponent blends, Mater. Lett. 192 (2017) 17–20, https://doi.org/10.1016/j.matlet.2017.01.063. [256] S.-Y. Gu, K. Zhang, J. Ren, H. Zhan, Melt rheology of polylactide/poly(butylene adipate-co-terephthalate) blends, Carbohydr. Polym. 74 (2008) 79–85, https:// doi.org/10.1016/j.carbpol.2008.01.017. [257] K. Li, J. Peng, L.-S. Turng, H.-X. Huang, Dynamic rheological behavior and morphology of polylactide/poly(butylenes adipate-co-terephthalate) blends with various composition ratios, Adv. Polym. Technol. 30 (2011) 150–157, https://doi.org/10. 1002/adv.20212. [258] M. Nofar, A. Maani, H. Sojoudi, M.C. Heuzey, P.J. Carreau, Interfacial and rheological properties of PLA/PBAT and PLA/PBSA blends and their morphological stability under shear flow, J. Rheol. 59 (2015) 317–333, https://doi.org/10. 1122/1.4905714. [259] M. Nofar, M.C. Heuzey, P.J. Carreau, M.R. Kamal, J. Randall, Coalescence in PLA-PBAT blends under shear flow: effects of blend preparation and PLA molecular weight, J. Rheol. 60 (2016) 637–648, https://doi.org/10.1122/1.4953446. [260] E.J. Dil, P. Carreau, B.D. Favis, Morphology, miscibility and continuity development in poly(lactic acid)/poly(butylene adipate-co-terephthalate) blends, Polymer 68 (2015) 202–212, https://doi.org/10.1016/j.polymer.2015.05.012. [261] H. Xiao, W. Lu, J.-T. Yeh, Crystallization behavior of fully biodegradable poly(lactic acid)/poly(butylene adipate-co-terephthalate) blends, Appl. Polym. Sci. 112 (2009) 3754–3763, https://doi.org/10.1002/app.29800. [262] J.-T. Yeh, C.-H. Tsou, C.-Y. Huang, K.-N. Chen, C.-S. Wu, W.-L. Chai, Compatible and crystallization properties of poly(lactic acid)/poly(butylene adipate-co-terephthalate) blends, J. Appl. Polym. Sci. (2009)https://doi.org/10.1002/app.30907. [263] E. Quero, A.J. Müller, F. Signori, M.-B. Coltelli, S. Bronco, Isothermal coldcrystallization of PLA/PBAT blends with and without the addition of acetyl tributyl citrate, Macromol. Chem. Phys. 213 (2011) 36–48, https://doi.org/10.1002/macp. 201100437. [264] B. Wang, X. Zhao, L. Wang, Isothermal crystallization and melting behaviors of biodegradable poly(lactic acid)/poly(butylene adipate-co-terephthalate) blends compatibilized by transesterification, Polym.-Plast. Technol. Eng. 52 (2013) 718–726, https://doi.org/10.1080/03602559.2012.762671. [265] H.-T. Chiu, S.-Y. Huang, Y.-F. Chen, M.-T. Kuo, T.-Y. Chiang, C.-Y. Chang, et al., Heat treatment effects on the mechanical properties and morphologies of poly (lactic acid)/poly (butylene adipate-co-terephthalate) blends, Int. J. Police Sci. Manag. 2013 (2013) 1–11, https://doi.org/10.1155/2013/951696. [266] F. Signori, M.-B. Coltelli, S. Bronco, Thermal degradation of poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) and their blends upon melt processing, Polym. Degrad. Stab. 94 (2009) 74–82, https://doi.org/10.1016/j. polymdegradstab.2008.10.004. [267] Y.-X. Weng, Y.-J. Jin, Q.-Y. Meng, L. Wang, M. Zhang, Y.-Z. Wang, Biodegradation behavior of poly(butylene adipate-co-terephthalate) (PBAT), poly(lactic acid) (PLA), and their blend under soil conditions, Polym. Test. 32 (2013) 918–926, https://doi. org/10.1016/j.polymertesting.2013.05.001. [268] P. Liewchirakorn, D. Aht-Ong, W. Chinsirikul, Practical approach in developing desirable peel-seal and clear lidding films based on poly(lactic acid) and poly(butylene adipate-co-terephthalate) blends, Packag. Technol. Sci. 31 (2017) 296–309, https://doi.org/10.1002/pts.2321. [269] S. Lee, J.W. Lee, Characterization and processing of biodegradable polymer blends of poly(lactic acid) with poly(butylene succinate adipate), Korea Aust. Rheol J. 17 (2005) 71–77 (doi=10.1.1.455.4151&rep=rep1&type=). [270] W. Pivsa-Art, S. Pivsa-Art, K. Fujii, K. Nomura, K. Ishimoto, Y. Aso, et al., Compression molding and melt-spinning of the blends of poly(lactic acid) and poly(butylene succinate-co-adipate), J. Appl. Polym. Sci. 132 (2014)https://doi.org/10.1002/ app.41856. [271] V. Ojijo, S.S. Ray, R. Sadiku, Role of specific interfacial area in controlling properties of immiscible blends of biodegradable polylactide and poly[(butylene succinate)co-adipate], ACS Appl. Mater. Interfaces 4 (2012) 6690–6701, https://doi.org/10. 1021/am301842e. [272] R. Wang, S. Wang, Y. Zhang, Morphology, rheological behavior, and thermal stability of PLA/PBSA/POSS composites, J. Appl. Polym. Sci. 113 (2009) 3095–3102, https://doi.org/10.1002/app.30333. [273] H. Eslami, M.R. Kamal, Effect of a chain extender on the rheological and mechanical properties of biodegradable poly(lactic acid)/poly[(butylene succinate)-coadipate] blends, J. Appl. Polym. Sci. 129 (2013) 2418–2428, https://doi.org/10. 1002/app.38449. [274] V. Ojijo, S.S. Ray, Super toughened biodegradable polylactide blends with nonlinear copolymer interfacial architecture obtained via facile in-situ reactive compatibilization, Polymer 80 (2015) 1–17, https://doi.org/10.1016/j.polymer. 2015.10.038. [275] V. Ojijo, S.S. Ray, R. Sadiku, Toughening of biodegradable polylactide/poly(butylene succinate-co-adipate) blends via in situ reactive compatibilization, ACS Appl. Mater. Interfaces 5 (2013) 4266–4276, https://doi.org/10.1021/am400482f. [276] Z.-Y. Gui, H.-R. Wang, Y. Gao, C. Lu, S.-J. Cheng, Morphology and melt rheology of biodegradable poly(lactic acid)/poly(butylene succinate adipate) blends: effect of blend compositions, Iran. Polym. J. 21 (2012) 81–89, https://doi.org/10.1007/ s13726-011-0009-7.

351

[277] H. Eslami, M.R. Kamal, Elongational rheology of biodegradable poly(lactic acid)/ poly[(butylene succinate)-co-adipate] binary blends and poly(lactic acid)/poly [(butylene succinate)-co-adipate]/clay ternary nanocomposites, J. Appl. Polym. Sci. 127 (2012) 2290–2306, https://doi.org/10.1002/app.37928. [278] Y. Deng, N. Thomas, Blending poly(butylene succinate) with poly(lactic acid): ductility and phase inversion effects, Eur. Polym. J. 71 (2015) 534–546, https://doi.org/ 10.1016/j.eurpolymj.2015.08.029. [279] J.W. Park, S.S. Im, Morphological changes during heating in poly(L-lactic acid)/poly (butylene succinate) blend systems as studied by synchrotron X-ray scattering, J. Polym. Sci. B Polym. Phys. 40 (2002) 1931–1939, https://doi.org/10.1002/polb. 10240. [280] J.W. Park, S.S. Im, Phase behavior and morphology in blends of poly(L-lactic acid) and poly(butylene succinate), J. Appl. Polym. Sci. 86 (2002) 647–655, https://doi. org/10.1002/app.10923. [281] A. Bhatia, R.K. Gupta, S.N. Bhattacharya, H.J. Choi, Compatibility of biodegradable poly (lactic acid) (PLA) and poly (butylene succinate) (PBS) blends for packaging application, Korea Aust. Rheol. J. 19 (2007) 125–131. [282] T. Yokohara, M. Yamaguchi, Structure and properties for biomass-based polyester blends of PLA and PBS, Eur. Polym. J. 44 (2008) 677–685, https://doi.org/10. 1016/j.eurpolymj.2008.01.008. [283] L.-Q. Xu, H.-X. Huang, Relaxation behavior of poly(lactic acid)/poly(butylene succinate) blend and a new method for calculating its interfacial tension, J. Appl. Polym. Sci. 125 (2012)https://doi.org/10.1002/app.36910. [284] D. Wu, L. Yuan, E. Laredo, M. Zhang, W. Zhou, Interfacial properties, viscoelasticity, and thermal behaviors of poly(butylene succinate)/polylactide blend, Ind. Eng. Chem. Res. 51 (2012) 2290–2298, https://doi.org/10.1021/ie2022288. [285] R. Wang, S. Wang, Y. Zhang, C. Wan, P. Ma, Toughening modification of PLLA/PBS blends via in situ compatibilization, Polym. Eng. Sci. 49 (2009) 26–33, https:// doi.org/10.1002/pen.21210. [286] M. Shibata, Y. Inoue, M. Miyoshi, Mechanical properties, morphology, and crystallization behavior of blends of poly(L-lactide) with poly(butylene succinate-co-Llactate) and poly(butylene succinate), Polymer 47 (2006) 3557–3564, https:// doi.org/10.1016/j.polymer.2006.03.065. [287] D. Ji, Z. Liu, X. Lan, F. Wu, B. Xie, M. Yang, Morphology, rheology, crystallization behavior, and mechanical properties of poly(lactic acid)/poly(butylene succinate)/ dicumyl peroxide reactive blends, J. Appl. Polym. Sci. 131 (2013)https://doi.org/ 10.1002/app.39580. [288] M. Harada, T. Ohya, K. Iida, H. Hayashi, K. Hirano, H. Fukuda, Increased impact strength of biodegradable poly(lactic acid)/poly(butylene succinate) blend composites by using isocyanate as a reactive processing agent, J. Appl. Polym. Sci. 106 (2007) 1813–1820, https://doi.org/10.1002/app.26717. [289] O. Persenaire, R. Quintana, Y. Lemmouchi, J. Sampson, S. Martin, L. Bonnaud, et al., Reactive compatibilization of poly(l-lactide)/poly(butylene succinate) blends through polyester maleation: from materials to properties, Polym. Int. 63 (2014) 1724–1731, https://doi.org/10.1002/pi.4700. [290] L. Li, G. Song, G. Tang, Novel biodegradable polylactide/poly(butylene succinate) composites via cross-linking with methylene diphenyl diisocyanate, Polym.-Plast. Technol. Eng. 52 (2013) 1183–1187, https://doi.org/10.1080/03602559.2013. 798817. [291] W. Zhang, Y. Xu, P. Wang, J. Hong, J. Liu, J. Ji, et al., Copolymer P(BS-co-LA) enhanced compatibility of PBS/PLA composite, J. Polym. Environ. 26 (2018) 3060–3068, https://doi.org/10.1007/s10924-018-1180-0. [292] H. Kun, Z. Wei, L. Xuan, Y. Xiubin, Biocompatibility of a novel poly(butyl succinate) and polylactic acid blend, ASAIO J. 58 (2012) 262–267, https://doi.org/10.1097/ mat.0b013e31824709ee. [293] L.D. Kimble, D. Bhattacharyya, In vitro degradation effects on strength, stiffness, and creep of PLLA/PBS: a potential stent material, Int. J. Polym. Mater. Polym. Biomater. 64 (2015) 299–310, https://doi.org/10.1080/00914037. 2014.945203. [294] A. Kovalovs, N. Jelinska, M. Kalnins, A. Chate, Search for composition of nanoparticles containing poly (vinyl alcohol)/poly (vinyl acetate) blend composites having the highest value of the modulus of elasticity by the response surface methodology, IOP Conference Series: Mater. Sci. Eng, 111, , 2016, 012006. https://doi.org/ 10.1088/1757-899x/111/1/012006. [295] A.M. Gajria, V. Davé, R.A. Gross, S.P. McCarthy, Miscibility and biodegradability of blends of poly(lactic acid) and poly(vinyl acetate), Polymer 37 (1996) 437–444, https://doi.org/10.1016/0032-3861(96)82913-2. [296] J.P. Mahalik, G. Madras, Enzymatic degradation of poly(D,L-lactide) and its blends with poly(vinyl acetate), J. Appl. Polym. Sci. 101 (2006) 675–680, https://doi.org/ 10.1002/app.23817. [297] X. Shuai, Y. He, N. Asakawa, Y. Inoue, Miscibility and phase structure of binary blends of poly(L-lactide) and poly(vinyl alcohol), J. Appl. Polym. Sci. 81 (2001) 762–772, https://doi.org/10.1002/app.1493. [298] H. Tsuji, H. Muramatsu, Blends of aliphatic polyesters. IV. Morphology, swelling behavior, and surface and bulk properties of blends from hydrophobic poly(L-lactide) and hydrophilic poly(vinyl alcohol), J. Appl. Polym. Sci. 81 (2001) 2151–2160, https://doi.org/10.1002/app.1651. [299] J.-T. Yeh, M.-C. Yang, C.-J. Wu, X. Wu, C.-S. Wu, Study on the crystallization kinetic and characterization of poly(lactic acid) and poly(vinyl alcohol) blends, Polym.-Plast. Technol. Eng. 47 (2008) 1289–1296, https://doi.org/10.1080/ 03602550802497958. [300] H.-Z. Li, S.-C. Chen, Y.-Z. Wang, Thermoplastic PVA/PLA blends with improved processability and hydrophobicity, Ind. Eng. Chem. Res. 53 (2014) 17355–17361, https://doi.org/10.1021/ie502531w. [301] N.H.A. Tran, H. Brünig, C. Hinüber, G. Heinrich, Melt spinning of biodegradable nanofibrillary structures from poly(lactic acid) and poly(vinyl alcohol) blends,

352

[302]

[303]

[304]

[305]

[306]

[307]

[308]

[309]

[310]

[311]

[312]

[313]

[314]

[315]

[316]

[317]

[318]

[319]

[320]

[321]

[322]

[323]

[324]

[325]

[326]

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360 Macromol. Mater. Eng. 299 (2013) 219–227, https://doi.org/10.1002/mame. 201300125. R. Neppalli, V. Causin, A. Marigo, M. Meincken, P. Hartmann, A.J.V. Reenen, Effect of electrospun ethylene vinyl alcohol copolymer (EVOH) fibres on the structure, morphology, and properties of poly(lactic acid) (PLA), Polymer 54 (2013) 5909–5919, https://doi.org/10.1016/j.polymer.2013.08.046. C.M. Lee, E.S. Kim, J. Yoon, Reactive blending of poly (L-lactic acid) with poly(ethylene- co-vinyl alcohol), J. Appl. Polym. Sci. 98 (2005) 886–890, https://doi.org/ 10.1002/app.22193. W. Zhang, Z. Gui, C. Lu, S. Cheng, D. Cai, Y. Gao, Improving transparency of incompatible polymer blends by reactive compatibilization, Mater. Lett. 92 (2013) 68–70, https://doi.org/10.1016/j.matlet.2012.10.060. Z. Gui, W. Zhang, C. Lu, S. Cheng, Improving the barrier properties of poly(lactic acid) by blending with poly(ethylene-co-vinyl alcohol), J. Macromol. Sci., Phys. 52 (2012) 685–700, https://doi.org/10.1080/00222348.2012.720180. H. Wu, C.-P. Wu, M.C. Kuo, Y. Tsai, Characterization and properties of reactive poly (lactic acid)/ethylene–vinyl alcohol copolymer blends with chain-extender, J. Polym. Environ. 24 (2016) 129–138, https://doi.org/10.1007/s10924-016-0755-x. X. Ma, J. Yu, N. Wang, Compatibility characterization of poly(lactic acid)/poly(propylene carbonate) blends, J. Polym. Sci. B Polym. Phys. 44 (2006) 94–101, https:// doi.org/10.1002/polb.20669. M. Gao, Z. Ren, S. Yan, J. Sun, X. Chen, An optical microscopy study on the phase structure of poly(L-lactide acid)/poly(propylene carbonate) blends, J. Phys. Chem. B 116 (2012) 9832–9837, https://doi.org/10.1021/jp3041378. W. Ning, Z. Xingxiang, Y. Jiugao, F. Jianming, Partially miscible poly(lactic acid)blend-poly(propylene carbonate) filled with carbon black as conductive polymer composite, Polym. Int. 57 (2008) 1027–1035, https://doi.org/10.1002/pi.2442. M. Yao, H. Deng, F. Mai, K. Wang, Q. Zhang, F. Chen, et al., Modification of poly(lactic acid)/poly(propylene carbonate) blends through melt compounding with maleic anhydride, Express Polym Lett 5 (2011) 937–949, https://doi.org/10.3144/ expresspolymlett.2011.92. J. Gao, H. Bai, Q. Zhang, Y. Gao, L. Chen, Q. Fu, Effect of homopolymer poly(vinyl acetate) on compatibility and mechanical properties of poly(propylene carbonate)/poly(lactic acid) blends, Express Polym Lett 6 (2012) 860–870, https://doi. org/10.3144/expresspolymlett.2012.92. Y. Chen, Y. Peng, W.Y. Liu, G.S. Zeng, X.G. Li, X.H. Yan, Study on the mechenical properties of PPC/PLA blends modified by POSS, Adv. Mater. Res. 741 (2013) 28–32, https://doi.org/10.4028/www.scientific.net/amr.741.28. L. Zhou, G. Zhao, W. Jiang, Effects of catalytic transesterification and composition on the toughness of poly(lactic acid)/poly(propylene carbonate) blends, Ind. Eng. Chem. Res. 55 (2016) 5565–5573, https://doi.org/10.1021/acs.iecr. 6b00315. J.-B. Zeng, Y.-D. Li, W.-D. Li, K.-K. Yang, X.-L. Wang, Y.-Z. Wang, Synthesis and properties of poly(ester urethane)s consisting of poly(L-lactic acid) and poly(ethylene succinate) segments, Ind. Eng. Chem. Res. 48 (2009) 1706–1711, https://doi.org/ 10.1021/ie801391m. J. Lu, Z. Qiu, W. Yang, Fully biodegradable blends of poly(l-lactide) and poly(ethylene succinate): miscibility, crystallization, and mechanical properties, Polymer 48 (2007) 4196–4204, https://doi.org/10.1016/j.polymer.2007.05.035. X. Fan, J. Ruan, J. Chen, Z. Zhou, J. Zou, The effect of poly(ethylene succinate) on mechanical properties of PLLA/PES blend prepared by melt-blending, J. Macromol. Sci., Part B: Phys. 50 (2011) 493–502, https://doi.org/10.1080/ 00222348.2011.575026. L.I. Ramdhanie, S.R. Aubuchon, E.D. Boland, D.C. Knapp, C.P. Barnes, D.G. Simpson, et al., Thermal and mechanical characterization of electrospun blends of poly(lactic acid) and poly(glycolic acid), Polym. J. 38 (2006) 1137–1145, https://doi.org/10. 1295/polymj.pj2006062. Y. You, S.W. Lee, J.H. Youk, B.-M. Min, S.J. Lee, W.H. Park, In vitro degradation behaviour of non-porous ultra-fine poly(glycolic acid)/poly(L-lactic acid) fibres and porous ultra-fine poly(glycolic acid) fibres, Polym. Degrad. Stab. 90 (2005) 441–448, https://doi.org/10.1016/j.polymdegradstab.2005.04.015. Y. You, J.H. Youk, S.W. Lee, B.-M. Min, S.J. Lee, W.H. Park, Preparation of porous ultrafine PGA fibers via selective dissolution of electrospun PGA/PLA blend fibers, Mater. Lett. 60 (2006) 757–760, https://doi.org/10.1016/j.matlet.2005.10.007. A. Pandey, G. Pandey, P. Aswath, Synthesis of polylactic acid–polyglycolic acid blends using microwave radiation, J. Mech. Behav. Biomed. Mater. 1 (2008) 227–233, https://doi.org/10.1016/j.jmbbm.2007.12.001. T. Iwata, ChemInform abstract: biodegradable and bio-based polymers: future prospects of eco-friendly plastics, Angew. Chem. Int. Ed. 46 (2015) 3210–3215, https://doi.org/10.1002/chin.201518345. L. Shen, E. Worrell, M.K. Patel, Comparing life cycle energy and GHG emissions of bio-based PET, recycled PET, PLA, and man-made cellulosics, Biofuels Bioprod. Biorefin. 6 (2012) 625–639, https://doi.org/10.1002/bbb.1368. M. Winnacker, B. Rieger, Biobased polyamides: recent advances in basic and applied research, Macromol. Rapid Commun. 37 (2016) 1391–1413, https://doi.org/ 10.1002/marc.201600181. W. Zhang, L. Chen, Y. Zhang, Surprising shape-memory effect of polylactide resulted from toughening by polyamide elastomer, Polymer 50 (2009) 1311–1315, https://doi.org/10.1016/j.polymer.2009.01.032. G. Stoclet, R. Seguela, J.-M. Lefebvre, Morphology, thermal behavior and mechanical properties of binary blends of compatible biosourced polymers: Polylactide/ polyamide11, Polymer 52 (2011) 1417–1425, https://doi.org/10.1016/j.polymer. 2011.02.002. R. Patel, D.A. Ruehle, J.R. Dorgan, P. Halley, D. Martin, Biorenewable blends of polyamide-11 and polylactide, Polym. Eng. Sci. 54 (2013) 1523–1532, https:// doi.org/10.1002/pen.23692.

[327] J. Gug, M.J. Sobkowicz, Improvement of the mechanical behavior of bioplastic poly (lactic acid)/polyamide blends by reactive compatibilization, J. Appl. Polym. Sci. 133 (2016)https://doi.org/10.1002/app.43350. [328] A.M. Zolali, V. Heshmati, B.D. Favis, Ultratough co-continuous PLA/PA11 by interfacially percolated poly(ether-b-amide), Macromolecules 50 (2016) 264–274, https://doi.org/10.1021/acs.macromol.6b02310. [329] V. Heshmati, A.M. Zolali, B.D. Favis, Morphology development in poly (lactic acid)/polyamide11 biobased blends: chain mobility and interfacial interactions, Polymer 120 (2017) 197–208, https://doi.org/10.1016/j.polymer.2017. 05.056. [330] V. Heshmati, B.D. Favis, High performance poly (lactic acid)/bio-polyamide11 through controlled chain mobility, Polymer 123 (2017) 184–193, https://doi.org/ 10.1016/j.polymer.2017.07.009. [331] F.-C. Pai, S.-M. Lai, H.-H. Chu, Characterization and properties of reactive poly(lactic acid)/polyamide 610 biomass blends, J. Appl. Polym. Sci. 130 (2013) 2563–2571, https://doi.org/10.1002/app.39473. [332] A.R. Kakroodi, Y. Kazemi, M. Nofar, C.B. Park, Tailoring poly(lactic acid) for packaging applications via the production of fully bio-based in situ microfibrillar composite films, Chem. Eng. J. 308 (2017) 772–782, https://doi.org/10.1016/j.cej.2016.09. 130. [333] B. Ferrero, V. Fombuena, O. Fenollar, T. Boronat, R. Balart, Development of natural fiber-reinforced plastics (NFRP) based on biobased polyethylene and waste fibers from Posidonia oceanica seaweed, Polym. Compos. 36 (2014) 1378–1385, https:// doi.org/10.1002/pc.23042. [334] G.F. Brito, P. Agrawal, T.J.A. Mélo, Mechanical and morphological properties of PLA/ BioPE blend compatibilized with E-GMA and EMA-GMA copolymers, Macromol. Symp. 367 (2016) 176–182, https://doi.org/10.1002/masy.201500158. [335] Plastic Moulding CA, All About Plastic Moulding, www.plasticmoulding.ca/polymers/polyethylene.htm. [336] Y. Wang, M.A. Hillmyer, Polyethylene-poly(L-lactide) diblock copolymers: synthesis and compatibilization of poly(L-lactide)/polyethylene blends, J. Polym. Sci. A Polym. Chem. 39 (2001) 2755–2766, https://doi.org/10.1002/pola.1254. [337] K.S. Anderson, S.H. Lim, M.A. Hillmyer, Toughening of polylactide by melt blending with linear low-density polyethylene, J. Appl. Polym. Sci. 89 (2003) 3757–3768, https://doi.org/10.1002/app.12462. [338] Anderson K.S. Anderson, M.A. Hillmyer, The influence of block copolymer microstructure on the toughness of compatibilized polylactide/polyethylene blends, Polymer 45 (2004) 8809–8823, https://doi.org/10.1016/j.polymer.2004.10.047. [339] F. Kim, C.N. Choi, Y.D. Kim, K.Y. Lee, M.S. Lee, Compatibilization of immiscible poly (L-lactide) and low density polyethylene blends, Fiber Polym. 5 (2004) 270–274, https://doi.org/10.1007/bf02875524. [340] Z. Su, Q. Li, Y. Liu, H. Xu, W. Guo, C. Wu, Phase structure of compatibilized poly(lactic acid)/linear low-density polyethylene blends, J. Macromol. Sci., Part B: Phys. 48 (2009) 823–833. [341] G. Singh, H. Bhunia, A. Rajor, R.N. Jana, V. Choudhary, Mechanical properties and morphology of polylactide, linear low-density polyethylene, and their blends, J. Appl. Polym. Sci. 118 (2010) 496–502. [342] G. Singh, H. Bhunia, A. Rajor, V. Choudhary, Thermal properties and degradation characteristics of polylactide, linear low density polyethylene, and their blends, Polym. Bull. 66 (2010) 939–953, https://doi.org/10.1007/s00289010-0367-x. [343] S. Djellali, N. Haddaoui, Z.Z.S. Djellali, N. Haddaoui, T. Sadoun, A. Bergeret, Y. Grohens, Structural, morphological and mechanical characteristics of polyethylene, poly(lactic acid) and poly(ethylene-co-glycidyl methacrylate) blends, Iran. Polym. J. 22 (2013) 245–257, https://doi.org/10.1007/s13726-013-0126-6. [344] S.-M. Lai, K.-C. Hung, H.C. Kao, L.-C. Liu, X.F. Wang, Synergistic effects by compatibilization and annealing treatment of metallocene polyethylene/PLA blends, J. Appl. Polym. Sci. 130 (2013) 2399–2409, https://doi.org/10.1002/app. 39437. [345] A.M. Zolali, B.D. Favis, Toughening of cocontinuous polylactide/polyethylene blends via an interfacially percolated intermediate phase, Macromolecules 51 (2018) 3572–3581, https://doi.org/10.1021/acs.macromol.8b00464. [346] M. Thurber, Y. Xu, J.C. Myers, T.P. Lodge, C.W. Macosko, Accelerating reactive compatibilization of PE/PLA blends by an interfacially localized catalyst, ACS Macro Lett. 4 (2014) 30–33, https://doi.org/10.1021/mz500770y. [347] X. Lu, L. Tang, L. Wang, J. Zhao, D. Li, Z. Wu, et al., Morphology and properties of biobased poly (lactic acid)/high-density polyethylene blends and their glass fiber reinforced composites, Polym. Test. 54 (2016) 90–97, https://doi.org/10.1016/j. polymertesting.2016.06.025. [348] K. Hamad, M. Kaseem, F. Deri, Melt rheology of poly(lactic acid)/low density polyethylene polymer blends, Adv. Chem. Eng. Sci. 01 (2011) 208–214, https://doi.org/ 10.4236/aces.2011.14030. [349] K. Hamad, M. Kaseem, F. Deri, Poly(lactic acid)/low density polyethylene polymer blends: preparation and characterization, Asia Pac. J. Chem. Eng. 7 (2012) S310–S316, https://doi.org/10.1002/apj.1649. [350] G. Jiang, H.-X. Huang, Z.-K. Chen, Rheological responses and morphology of polylactide/linear low density polyethylene blends produced by different mixing type, Polym.-Plast. Technol. Eng. 50 (2011) 1035–1039, https://doi.org/10.1080/ 03602559.2011.557822. [351] H. Balakrishnan, A. Hassan, M.U. Wahit, Mechanical, thermal, and morphological properties of Polylactic acid/linear low density polyethylene blends, J. Elastomers Plast. 42 (2010) 223–239, https://doi.org/10.1177/0095244310362403. [352] T. Bee, C. Ratnam, L.T. Sin, T.-T. Tee, W.-K. Wong, J.-X. Lee, et al., Effects of electron beam irradiation on the structural properties of polylactic acid/polyethylene blends, Nucl. Instrum. Methods Phys. Res., Sect. B 334 (2014) 18–27, https://doi. org/10.1016/j.nimb.2014.04.024.

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360 [353] M. Omura, T. Tsukegi, Y. Shirai, H. Nishida, T. Endo, Thermal degradation behavior of poly(lactic acid) in a blend with polyethylene, Ind. Eng. Chem. Res. 45 (2006) 2949–2953, https://doi.org/10.1021/ie051446x. [354] F. Rezgui, C. Gsell, A. Dahoun, J. Hiver, T. Sadoun, Plastic deformation of low-density polyethylene reinforced with biodegradable polylactide, part 1: microstructural analysis and tensile behavior at constant true strain-rate, Polym. Eng. Sci. 51 (2010) 117–125, https://doi.org/10.1002/pen.21797. [355] F. Rezgui, C. Gsell, A. Dahoun, J. Hiver, T. Sadoun, Plastic deformation of low-density polyethylene reinforced with biodegradable polylactide, part 2: creep characterization and modeling, Polym. Eng. Sci. 51 (2010) 126–132, https://doi.org/10.1002/ pen.21796. [356] N. Reddy, D. Nama, Y. Yang, Polylactic acid/polypropylene polyblend fibers for better resistance to degradation, Polym. Degrad. Stab. 93 (2008) 233–241, https://doi. org/10.1016/j.polymdegradstab.2007.09.005. [357] H.-S. Kim, H.-J. Kim, Miscibility and performance evaluation of natural-flour-filled PP/PBS and PP/PLA bio-composites, Fibers Polym. 14 (2013) 793–803, https:// doi.org/10.1007/s12221-013-0793-0. [358] N. Ploypetchara, P. Suppakul, D. Atong, C. Pechyen, Blend of polypropylene/poly (lactic acid) for medical packaging application: physicochemical, thermal, mechanical, and barrier properties, Energy Procedia 56 (2014) 201–210, https://doi. org/10.1016/j.egypro.2014.07.150. [359] Z. Ying-Chen, W. Hong-Yan, Q. Yi-Ping, Morphology and properties of hybrid composites based on polypropylene/polylactic acid blend and bamboo fiber, Bioresour. Technol. 101 (2010) 7944–7950, https://doi.org/10.1016/j. biortech.2010.05.007. [360] S. Pivsa-Art, J. Kord-Sa-Ard, W. Pivsa-Art, R. Wongpajan, N. O-Charoen, S. Pavasupree, et al., Effect of compatibilizer on PLA/PP blend for injection molding, Energy Procedia 89 (2016) 353–360, https://doi.org/10.1016/j.egypro.2016.05. 046. [361] T.W. Yoo, H.G. Yoon, S.J. Choi, M.S. Kim, Y.H. Kim, W.N. Kim, Effects of compatibilizers on the mechanical properties and interfacial tension of polypropylene and poly(lactic acid) blends, Macromol. Res. 18 (2010) 583–588, https:// doi.org/10.1007/s13233-010-0613-y. [362] H.S. Lee, J.D. Kim, Effect of a hybrid compatibilizer on the mechanical properties and interfacial tension of a ternary blend with polypropylene, poly(lactic acid), and a toughening modifier, Polym. Compos. 33 (2012) 1154–1161, https://doi. org/10.1002/pc.22244. [363] P. Choudhary, S. Mohanty, S.K. Nayak, L. Unnikrishnan, Poly(L-lactide)/polypropylene blends: evaluation of mechanical, thermal, and morphological characteristics, J. Appl. Polym. Sci. 121 (2011) 3223–3237, https://doi.org/10.1002/app.33866. [364] Y. Xu, J. Loi, P. Delgado, V. Topolkaraev, R.J. McEneany, C.W. Macosko, M.A. Hillmyer, Reactive compatibilization of polylactide/polypropylene blends, Ind. Eng. Chem. Res. 54 (2015) 6108–6114, https://doi.org/10.1021/acs.iecr. 5b00882. [365] Z. Lin, C. Chen, Z. Guan, B. Xu, X. Li, Z. Huang, Polypropylene/poly (lactic acid) semibiocomposites modified with two kinds of intumescent flame retardants, Polym.-Plast. Technol. Eng. 51 (2012) 991–997, https://doi.org/10.1080/ 03602559.2012.680559. [366] G. Biresaw, C.J. Carriere, Interfacial tension of poly(lactic acid)/polystyrene blends, J. Polym. Sci. B Polym. Phys. 40 (2002) 2248–2258, https://doi.org/10.1002/polb. 10290. [367] P. Sarazin, B.D. Favis, Morphology control in co-continuous poly(L-lactide)/polystyrene blends: a route towards highly structured and interconnected porosity in poly (L-lactide) materials, Biomacromolecules 4 (2003) 1669–1679, https://doi.org/10. 1021/bm030034. [368] Z. Yuan, B.D. Favis, Macroporous poly(L-lactide) of controlled pore size derived from the annealing of co-continuous polystyrene/poly(L-lactide) blends, Biomaterials 25 (2004) 2161–2170, https://doi.org/10.1016/j.biomaterials.2003.08.060. [369] B.O. Leung, A.P. Hitchcock, R. Cornelius, J.L. Brash, A. Scholl, A. Doran, X-ray spectromicroscopy study of protein adsorption to a polystyrene−polylactide blend, Biomacromolecules 10 (2009) 1838–1845, https://doi.org/10.1021/ bm900264w. [370] B.O. Leung, A.P. Hitchcock, J.L. Brash, A. Scholl, A. Doran, Phase segregation in polystyrene−polylactide blends, Macromolecules 42 (2009) 1679–1684, https://doi. org/10.1021/ma802176b. [371] L. Gu, E.E. Nessim, C.W. Macosko, Reactive compatibilization of poly(lactic acid)/ polystyrene blends and its application to preparation of hierarchically porous poly(lactic acid), Polymer 134 (2018) 104–116, https://doi.org/10.1016/j. polymer.2017.11.054. [372] G. Biresaw, C. Carriere, Compatibility and mechanical properties of blends of polystyrene with biodegradable polyesters, Compos. A: Appl. Sci. Manuf. 35 (2004) 313–320, https://doi.org/10.1016/j.compositesa.2003.09.020. [373] A. Mohamed, S.H. Gordon, G. Biresaw, Poly(lactic acid)/polystyrene bioblends characterized by thermogravimetric analysis, differential scanning calorimetry, and photoacoustic infrared spectroscopy, J. Appl. Polym. Sci. 106 (2007) 1689–1696, https://doi.org/10.1002/app.26783. [374] E. Zuza, A. Lejardi, J.M. Ugartemendia, N. Monasterio, E. Meaurio, J.-R. Sarasua, Compatibilization through specific interactions and dynamic fragility in poly(D,Llactide)/polystyrene blends, Macromol. Chem. Phys. 209 (2008) 2423–2433, https://doi.org/10.1002/macp.200800443. [375] K. Hamad, M. Kaseem, F. Deri, Rheological and mechanical properties of poly(lactic acid)/polystyrene polymer blend, Polym. Bull. 65 (2010) 509–519, https://doi.org/ 10.1007/s00289-010-0354-2. [376] K. Hamad, M. Kaseem, F. Deri, Effect of recycling on rheological and mechanical properties of poly(lactic acid)/polystyrene polymer blend, J. Mater. Sci. 46 (2010) 3013–3019, https://doi.org/10.1007/s10853-010-5179-8.

353

[377] M. Kaseem, Y.G. Ko, Melt flow behavior and processability of polylactic acid/polystyrene (PLA/PS) polymer blends, J. Polym. Environ. 25 (2016) 994–998, https:// doi.org/10.1007/s10924-016-0873-5. [378] Y. Li, H. Shimizu, Improvement in toughness of poly(L-lactide) (PLLA) through reactive blending with acrylonitrile–butadiene–styrene copolymer (ABS): morphology and properties, Eur. Polym. J. 45 (2009) 738–746, https://doi.org/10.1016/j. eurpolymj.2008.12.010. [379] M.Y. Jo, Y.J. Ryu, J.H. Ko, J.-S. Yoon, Effects of compatibilizers on the mechanical properties of ABS/PLA composites, J. Appl. Polym. Sci. 125 (2012)https://doi.org/ 10.1002/app.36732. [380] I.-J. Choe, J.H. Lee, J.H. Yu, J.-S. Yoon, Mechanical properties of acrylonitrilebutadiene-styrene copolymer/poly(L-lactic acid) blends and their composites, J. Appl. Polym. Sci. 131 (2014)https://doi.org/10.1002/app.40329. [381] W. Dong, M. He, H. Wang, F. Ren, J. Zhang, X. Zhao, et al., PLLA/ABS blends compatibilized by reactive comb polymers: double Tg depression and significantly improved toughness, ACS Sustain. Chem. Eng. 3 (2015) 2542–2550, https://doi. org/10.1021/acssuschemeng.5b00740. [382] R. Vadori, M. Misra, A.K. Mohanty, Sustainable biobased blends from the reactive extrusion of polylactide and acrylonitrile butadiene styrene, J. Appl. Polym. Sci. 133 (2016)https://doi.org/10.1002/app.43771. [383] R. Vadori, M. Misra, A.K. Mohanty, Statistical optimization of compatibilized blends of poly(lactic acid) and acrylonitrile butadiene styrene, J. Appl. Polym. Sci. 134 (2017) 44516–44526, https://doi.org/10.1002/app.44516. [384] N. Wu, H. Zhang, Toughening of poly(L-lactide) modified by a small amount of acrylonitrile−butadiene−styrene core-shell copolymer, J. Appl. Polym. Sci. 132 (2015) 42554, https://doi.org/10.1002/app.42554. [385] G. Zhang, J. Zhang, S. Wang, D. Shen, Miscibility and phase structure of binary blends of polylactide and poly(methyl methacrylate), J. Polym. Sci. B Polym. Phys. 41 (2003) 23–30, https://doi.org/10.1002/polb.10353. [386] D. Cossement, R. Gouttebaron, V. Cornet, P. Viville, M. Hecq, R. Lazzaroni, PLAPMMA blends: a study by XPS and ToF-SIMS, Appl. Surf. Sci. 252 (2006) 6636–6639, https://doi.org/10.1016/j.apsusc.2006.02.225. [387] M. Gonzalez-Garzon, S. Shahbikian, M.A. Huneault, Properties and phase structure of melt-processed PLA/PMMA blend, J. Polym. Res. 25 (2018) 58, https://doi.org/ 10.1002/app.42677. [388] C. Samuel, J.-M. Raquez, P. Dubois, PLLA/PMMA blends: a shear-induced miscibility with tunable morphologies and properties? Polymer 54 (2013) 3931–3939, https://doi.org/10.1016/j.polymer.2013.05.021. [389] C. Samuel, S. Barrau, J.-M. Lefebvre, J.-M. Raquez, P. Dubois, Designing multipleshape memory polymers with miscible polymer blends: evidence and origins of a triple-shape memory effect for miscible PLLA/PMMA blends, Macromolecules 47 (2014) 6791–6803, https://doi.org/10.1021/ma500846x. [390] C. Samuel, J. Cayuela, I. Barakat, A.J. Müller, J.-M. Raquez, P. Dubois, Stereocomplexation of polylactide enhanced by poly(methyl methacrylate): improved processability and thermomechanical properties of stereocomplexable polylactide-based materials, Appl. Mater. Interfaces 5 (2013) 11797–11807, https://doi.org/10.1021/am403443m. [391] R.-Y. Bao, W. Yang, Z.-Y. Liu, B.-H. Xie, M.-B. Yang, Polymorphism of a highmolecular-weight racemic poly(l-lactide)/poly(d-lactide) blend: effect of melt blending with poly(methyl methacrylate), RSC Adv. 5 (2015) 19058–19066, https://doi.org/10.1039/c5ra00691k. [392] X. Hao, J. Kaschta, X. Liu, Y. Pan, D.W. Schubert, Entanglement network formed in miscible PLA/PMMA blends and its role in rheological and thermo-mechanical properties of the blends, Polymer 80 (2015) 38–45, https://doi.org/10.1016/j. polymer.2015.10.037. [393] J.-H. Wu, M.C. Kuo, C.-W. Chen, Physical properties and crystallization behavior of poly(lactide)/poly(methyl methacrylate)/silica composites, J. Appl. Polym. Sci. 132 (2015) 42378, https://doi.org/10.1002/app.42378. [394] J. Anakabe, A.M.Z. Huici, A. Eceiza, A. Arbelaiz, The effect of the addition of poly(styrene-co-glycidyl methacrylate) copolymer on the properties of polylactide/poly (methyl methacrylate) blend, J. Appl. Polym. Sci. 133 (2016) 43935, https://doi. org/10.1002/app.43935. [395] B. Imre, K. Renner, B. Pukanszky, Interactions, structure and properties in poly(lactic acid)/thermoplastic polymer blends, Express Polym Lett 8 (2014) 2–14, https:// doi.org/10.3144/expresspolymlett.2014.2. [396] B. Girija, R. Sailaja, G. Madras, Thermal degradation and mechanical properties of PET blends, Polym. Degrad. Stab. 90 (2005) 147–153, https://doi.org/10.1016/j. polymdegradstab.2005.03.003. [397] H. Chen, M. Pyda, P. Cebe, Non-isothermal crystallization of PET/PLA blends, Thermochim. Acta 492 (2009) 61–66, https://doi.org/10.1016/j.tca.2009.04.023. [398] Y. Fu, L. Liao, L. Yang, Y. Lan, L. Mei, Y. Liu, et al., Molecular dynamics and dissipative particle dynamics simulations for prediction of miscibility in polyethylene terephthalate/polylactide blends, Mol. Simul. 39 (2012) 415–422, https://doi.org/10. 1080/08927022.2012.738294. [399] A. Torres-Huerta, D. Palma-Ramírez, M. Domínguez-Crespo, D.D. Angel-López, D.D.L. Fuente, Comparative assessment of miscibility and degradability on PET/ PLA and PET/chitosan blends, Eur. Polym. J. 61 (2014) 285–299, https://doi.org/ 10.1016/j.eurpolymj.2014.10.016. [400] K. Li, B. Mao, P. Cebe, Electrospun fibers of poly(ethylene terephthalate) blended with poly(lactic acid), J. Therm. Anal. Calorim. 116 (2013) 1351–1359, https:// doi.org/10.1007/s10973-013-3583-4. [401] A.R. Mclauchlin, O.R. Ghita, Studies on the thermal and mechanical behavior of PLA-PET blends, J. Appl. Polym. Sci. 133 (2016) 44147, https://doi.org/10.1002/ app.44147. [402] A.M. Torres-Huerta, D.D. Angel-López, M.A. Domínguez-Crespo, D. Palma-Ramírez, M.E. Perales-Castro, A. Flores-Vela, Morphological and mechanical properties

354

[403]

[404]

[405]

[406]

[407]

[408]

[409]

[410]

[411]

[412]

[413]

[414]

[415]

[416]

[417]

[418]

[419]

[420]

[421]

[422]

[423]

[424]

[425]

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360 dependence of PLA amount in PET matrix processed by single-screw extrusion, Polym.-Plast. Technol. Eng. 55 (2016) 672–683, https://doi.org/10.1080/ 03602559.2015.1132433. W.-R. Jiang, R.-Y. Bao, W. Yang, Z.-Y. Liu, B.-H. Xie, M.-B. Yang, Morphology, interfacial and mechanical properties of polylactide/poly(ethylene terephthalate glycol) blends compatibilized by polylactide-g-maleic anhydride, Mater. Des. 59 (2014) 524–531, https://doi.org/10.1016/j.matdes.2014.03.016. F.L. Mantia, L. Botta, M. Morreale, R. Scaffaro, Effect of small amounts of poly(lactic acid) on the recycling of poly(ethylene terephthalate) bottles, Polym. Degrad. Stab. (2011) 21–24, https://doi.org/10.1016/j.polymdegradstab.2011.10.017. M.L.D. Lorenzo, P. Rubino, M. Cocca, Miscibility and properties of poly(l-lactic acid)/poly(butylene terephthalate) blends, Eur. Polym. J. 49 (2013) 3309–3317, https://doi.org/10.1016/j.eurpolymj.2013.06.038. M.W. Kim, S.M. Hong, D. Lee, K. Park, T.J. Kang, J.R. Youn, Chain extension effects of para-phenylene diisocyanate on crystallization behavior and biodegradability of poly(lactic acid)/poly(butylene terephthalate) blends, Adv. Compos. Mater. 19 (2010) 331–348, https://doi.org/10.1163/092430409x12605406698471. C. Samthong, J. Seemork, S. Nobukawa, M. Yamaguchi, P. Praserthdam, A. Somwangthanaroj, Morphology, structure, and properties of poly(lactic acid) microporous films containing poly(butylene terephthalate) fine fibers fabricated by biaxial stretching, J. Appl. Polym. Sci. 132 (2014) 41415, https://doi.org/10.1002/ app.41415. C. Samthong, C. Deetuam, M. Yamaguchi, P. Praserthdam, A. Somwangthanaroj, Effects of size and shape of dispersed poly(butylene terephthalate) on isothermal crystallization kinetics and morphology of poly(lactic acid) blends, Polym. Eng. Sci. 56 (2015) 258–268, https://doi.org/10.1002/pen.24246. S.-W. Lin, Y.-Y. Cheng, Miscibility, thermal and mechanical properties of meltmixed poly(lactic acid)/poly(trimethylene terephthalate) blends, Polym.-Plast. Technol. Eng. 49 (2010) 1001–1009, https://doi.org/10.1080/03602559.2010. 482078. H. Zou, C. Yi, L. Wang, W. Xu, Crystallization, hydrolytic degradation, and mechanical properties of poly (trimethylene terephthalate)/poly(lactic acid) blends, Polym. Bull. 64 (2009) 471–481, https://doi.org/10.1007/s00289-009-0191-3. H. Zou, L. Wang, C. Yi, H. Gan, Thermal properties and non-isothermal crystallization behavior of poly(trimethylene terephthalate)/poly(lactic acid) blends, Polym. Int. (2011)https://doi.org/10.1002/pi.3087. S. Padee, S. Thumsorn, J.W. On, P. Surin, C. Apawet, T. Chaichalermwong, et al., Preparation of poly(lactic acid) and poly(trimethylene terephthalate) blend fibers for textile application, Energy Procedia 34 (2013) 534–541, https://doi.org/10. 1016/j.egypro.2013.06.782. V. Nagarajan, A.K. Mohanty, M. Misra, Reactive compatibilization of poly trimethylene terephthalate (PTT) and polylactic acid (PLA) using terpolymer: factorial design optimization of mechanical properties, Mater. Des. 110 (2016) 581–591, https://doi.org/10.1016/j.matdes.2016.08.022. N.G. Karsli, A. Aytac, Properties of alkali treated short flax fiber reinforced poly(lactic acid)/polycarbonate composites, Fiber Polym. 15 (2014) 2607–2612, https:// doi.org/10.1007/s12221-014-2607-4. J.B. Lee, Y.K. Lee, G.D. Choi, S.W. Na, T.S. Park, W.N. Kim, Compatibilizing effects for improving mechanical properties of biodegradable poly (lactic acid) and polycarbonate blends, Polym. Degrad. Stab. 96 (2011) 553–560, https://doi.org/10.1016/ j.polymdegradstab.2010.12.019. Y. Wang, S.M. Chiao, T.-F. Hung, S.-Y. Yang, Improvement in toughness and heat resistance of poly(lactic acid)/polycarbonate blend through twin-screw blending: Influence of compatibilizer type, J. Appl. Polym. Sci. 125 (2012)https://doi.org/10. 1002/app.36920. Y. Wang, S. Chiao, M.-T. Lai, S.-Y. Yang, The role of polycarbonate molecular weight in the poly(L-lactide) blends compatibilized with poly(butylene succinate-co-L-lactate), Polym. Eng. Sci. 53 (2012) 1171–1180, https://doi.org/10.1002/pen.23374. V.T. Phuong, M.-B. Coltelli, P. Cinelli, M. Cifelli, S. Verstichel, A. Lazzeri, Compatibilization and property enhancement of poly(lactic acid)/polycarbonate blends through triacetin-mediated interchange reactions in the melt, Polymer 55 (2014) 4498–4513, https://doi.org/10.1016/j.polymer.2014.06.070. Y. Srithep, W. Rungseesantivanon, B. Hararak, K. Suchiva, Processing and characterization of poly(lactic acid) blended with polycarbonate and chain extender, J. Polym. Eng. (2014) 665–672, https://doi.org/10.1515/polyeng-2013-0309. L. Lin, C. Deng, Y.-Z. Wang, Improving the impact property and heat-resistance of PLA/PC blends through coupling molecular chains at the interface, Polym. Adv. Technol. 26 (2015) 1247–1258, https://doi.org/10.1002/pat.3560. Y. Yuryev, A.K. Mohanty, M. Misra, Novel biocomposites from biobased PC/PLA blend matrix system for durable applications, Compos. Part B 130 (2017) 158–166, https://doi.org/10.1016/j.compositesb.2017.07.030. A.M. Harris, E.C. Lee, Durability of polylactide-based polymer blends for injectionmolded applications, J. Appl. Polym. Sci. (2012) 158–166, https://doi.org/10.1002/ app.38407. L. Chun-Yan, Z. Chi-Xing, W. Yu, Transesterification between poly(lactic acid) and polycarbonate under flow field and its influence on morphology of the blends, Acta Polym. Sin. 012 (2012) 1225–1233, https://doi.org/10.3724/sp.j. 1105.2012.12145. Y. Yuryev, A.K. Mohanty, M. Misra, Hydrolytic stability of polycarbonate/poly(lactic acid) blends and its evaluation via poly(lactic) acid median melting point depression, Polym. Degrad. Stab. 134 (2016) 227–236, https://doi.org/10.1016/j. polymdegradstab.2016.10.011. V. Sedlarik, O. Otgonzul, T. Kitano, A. Gregorova, M. Hrabalova, I. Junkar, et al., Effect of phase arrangement on solid state mechanical and thermal properties of polyamide 6/polylactide based co-polyester blends, J. Macromol. Sci., Part B: Phys. 51 (2011) 982–1001, https://doi.org/10.1080/00222348.2011.610265.

[426] F. Feng, L. Ye, Structure and property of polylactide/polyamide blends, J. Macromol. Sci., Part B: Phys. 49 (2010) 1117–1127, https://doi.org/10.1080/ 00222341003609179. [427] Y.-L. Wang, X. Hu, H. Li, X. Ji, Z.-M. Li, Polyamide-6/poly(lactic acid) blends compatibilized by the maleic anhydride grafted polyethylene-Octene elastomer, Polym.-Plast. Technol. Eng. 49 (2010) 1241–1246, https://doi.org/10.1080/ 03602559.2010.496418. [428] P. Kucharczyk, O. Otgonzu, T. Kitano, A. Gregorova, D. Kreuh, U. Cvelbar, et al., Correlation of morphology and viscoelastic properties of partially biodegradable polymer blends based on polyamide 6 and polylactide copolyester, Polym.-Plast. Technol. Eng. 51 (2012) 1432–1442, https://doi.org/10.1080/03602559.2012. 709296. [429] P. Kucharczyk, V. Sedlarik, N. Miskolczi, H. Szakacs, T. Kitano, Properties enhancement of partially biodegradable polyamide/polylactide blends through compatibilization with novel polyalkenyl-poly-maleic-anhydride-amide/imidebased additives, J. Reinf. Plast. Compos. 31 (2012) 189–202, https://doi.org/10. 1177/0731684411434150. [430] R. Khankrua, S. Pivsa-Art, H. Hiroyuki, S. Suttiruengwong, Effect of chain extenders on thermal and mechanical properties of poly(lactic acid) at high processing temperatures: potential application in PLA/polyamide 6 blend, Polym. Degrad. Stab. 108 (2014) 232–240, https://doi.org/10.1016/j.polymdegradstab.2014.04.019. [431] A. Nijenhuis, E. Colstee, D. Grijpma, A. Pennings, High molecular weight poly(Llactide) and poly(ethylene oxide) blends: thermal characterization and physical properties, Polymer 37 (1996) 5849–5857, https://doi.org/10.1016/s0032-3861 (96)00455-7. [432] H. Lee, R.M. Venable, A.D. Mackerell, R.W. Pastor, Molecular dynamics studies of polyethylene oxide and polyethylene glycol: hydrodynamic radius and shape anisotropy, Biophys. J. 95 (2008) 1590–1599, https://doi.org/10.1529/biophysj.108. 133025. [433] H. Younes, D. Cohn, Phase separation in poly(ethylene glycol)/poly(lactic acid) blends, Eur. Polym. J. 24 (1988) 765–773, https://doi.org/10.1016/0014-3057(88) 90013-4. [434] K. Nakane, Y. Hata, K. Morita, T. Ogihara, N. Ogata, Porous poly(L-lactic acid)/poly (ethylene glycol) blend films, J. Appl. Polym. Sci. 94 (2004) 965–970, https://doi. org/10.1002/app.20959. [435] K. Sungsanit, N. Kao, S.N. Bhattacharya, Properties of linear poly(lactic acid)/polyethylene glycol blends, Polym. Eng. Sci. 52 (2012) 108–116, https://doi.org/10. 1002/pen.22052. [436] M. Sheth, R.A. Kumar, V. Dave, R.A. Gross, S.P. McCarthy, et al., J. Appl. Polym. Sci. 66 (1997) 1495–1505, https://doi.org/10.1002/(SICI)1097-4628(19971121)66: 8b1495::AID-APP10N3.0.CO;2-3. [437] Y. Hu, Y. Hu, V. Topolkaraev, A. Hiltner, E. Baer, Aging of poly(lactide)/poly(ethylene glycol) blends. Part 2. Poly(lactide) with high stereoregularity, Polymer 44 (2003) 5711–5720, https://doi.org/10.1016/s0032-3861(03)00615-3. [438] Y. Hu, M. Rogunova, V. Topolkaraev, A. Hiltner, E. Baer, Aging of poly(lactide)/poly (ethylene glycol) blends. Part 1. Poly(lactide) with low stereoregularity, Polymer 44 (2003) 5701–5710, https://doi.org/10.1016/s0032-3861(03)00614-1. [439] W.-C. Lai, W.-B. Liau, T.-T. Lin, The effect of end groups of PEG on the crystallization behaviors of binary crystalline polymer blends PEG/PLLA, Polymer 45 (2004) 3073–3080, https://doi.org/10.1016/j.polymer.2004.03.003. [440] F. Hassouna, J.-M. Raquez, F. Addiego, P. Dubois, V. Toniazzo, D. Ruch, New approach on the development of plasticized polylactide (PLA): grafting of poly(ethylene glycol) (PEG) via reactive extrusion, Eur. Polym. J. 47 (2011) 2134–2144, https://doi.org/10.1016/j.eurpolymj.2011.08.001. [441] Z. Gui, Y. Xu, Y. Gao, C. Lu, S. Cheng, Novel polyethylene glycol-based polyestertoughened polylactide, Mater. Lett. 71 (2012) 63–65, https://doi.org/10.1016/j. matlet.2011.12.045. [442] K.-M. Choi, M.-C. Choi, D.-H. Han, T.-S. Park, C.-S. Ha, Plasticization of poly(lactic acid) (PLA) through chemical grafting of poly(ethylene glycol) (PEG) via in situ reactive blending, Eur. Polym. J. 49 (2013) 2356–2364, https://doi.org/10.1016/j. eurpolymj.2013.05.027. [443] B.-S. Park, J.C. Song, D.H. Park, K.-B. Yoon, PLA/chain-extended PEG blends with improved ductility, J. Appl. Polym. Sci. 123 (2011) 2360–2367, https://doi.org/10. 1002/app.34823. [444] J. Ahmed, S.K. Varshney, R. Auras, S.W. Hwang, Thermal and rheological properties of L-polylactide/polyethylene glycol/silicate nanocomposites films, J. Food Sci. 75 (2010) 97–108, https://doi.org/10.1111/j.1750-3841.2010.01809.x. [445] N. Elvassore, A. Bertucco, P. Caliceti, Production of insulin-loaded poly(ethylene glycol)/poly(L-lactide) (PEG/PLA) nanoparticles by gas antisolvent techniques, J. Pharm. Sci. 90 (2001) 1628–1636, https://doi.org/10.1002/jps.1113. [446] T. Riley, C.R. Heald, S. Stolnik, M.C. Garnett, L. Illum, S.S. Davis, S.M. King, R.K. Heenan, S.C. Purkiss, R.J. Barlow, P.R. Gellert, Washington C, Langmuir (2003) 19–8428. [447] T.M. Seck, F.P. Melchels, J. Feijen, D.W. Grijpma, Designed biodegradable hydrogel structures prepared by stereolithography using poly(ethylene glycol)/poly(D,Llactide)-based resins, J. Control. Release 148 (2010) 34–41, https://doi.org/10. 1016/j.jconrel.2010.07.111. [448] J.E. Oliveira, E.A. Moraes, J.M. Marconcini, L.H.C. Mattoso, G.M. Glenn, E.S. Medeiros, Properties of poly(lactic acid) and poly(ethylene oxide) solvent polymer mixtures and nanofibers made by solution blow spinning, J. Appl. Polym. Sci. 129 (2013) 3672–3681, https://doi.org/10.1002/app.39061. [449] T. Serra, M. Ortiz-Hernandez, E. Engel, J.A. Planell, M. Navarro, Relevance of PEG in PLA-based blends for tissue engineering 3D-printed scaffolds, Mater. Sci. Eng. C 38 (2014) 55–62, https://doi.org/10.1016/j.msec.2014.01.003. [450] J. Qiu, C. Xing, X. Cao, H. Wang, L. Wang, L. Zhao, et al., Miscibility and double glass transition temperature depression of poly(l-lactic acid) (PLLA)/poly

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

[451]

[452]

[453]

[454]

[455]

[456]

[457]

[458]

[459]

[460]

[461]

[462]

[463]

[464]

[465]

[466]

[467]

[468]

[469]

[470] [471]

[472]

[473]

[474]

[475]

(oxymethylene) (POM) blends, Macromolecules 46 (2013) 5806–5814, https:// doi.org/10.1021/ma401084y. J. Qiu, J. Guan, H. Wang, S. Zhu, X. Cao, Q.-L. Ye, et al., Enhanced crystallization rate of poly(L-lactic acid) (PLLA) by polyoxymethylene (POM) fragment crystals in the PLLA/POM blends with a small amount of POM, J. Phys. Chem. B 118 (2014) 7167–7176, https://doi.org/10.1021/jp412519g. S. Mathurosemontri, P. Auwongsuwan, S. Nagai, H. Hamada, The effect of injection speed on morphology and mechanical properties of Polyoxymethylene/poly(lactic acid) blends, Energy Procedia 56 (2014) 57–64, https://doi.org/10.1016/j.egypro. 2014.07.131. X. Guo, J. Zhang, J. Huang, Poly(lactic acid)/polyoxymethylene blends: morphology, crystallization, rheology, and thermal mechanical properties, Polymer 69 (2015) 103–109, https://doi.org/10.1016/j.polymer.2015.05.050. L. Zhang, S.H. Goh, S.Y. Lee, Miscibility and phase behavior of poly(D,L-lactide)/poly (p-vinylphenol) blends, J. Appl. Polym. Sci. 70 (1998) 811–816, https://doi.org/10. 1002/(sici)1097-4628(19981024)70:4b811::aid-app22N3.0.co;2-y. L. Zhang, S. Goh, S. Lee, Miscibility and crystallization behaviour of poly(l-lactide)/ poly(p-vinylphenol) blends, Polymer 39 (1998) 4841–4847, https://doi.org/10. 1016/s0032-3861(97)10167-7. E. Meaurio, E. Zuza, J.-R. Sarasua, Miscibility and specific interactions in blends of poly(L-lactide) with poly(vinylphenol), Macromolecules 38 (2005) 1207–1215, https://doi.org/10.1021/ma047818f. E. Meaurio, E. Zuza, J.-R. Sarasua, Direct measurement of the enthalpy of mixing in miscible blends of poly(DL-lactide) with poly(vinylphenol), Macromolecules 38 (2005) 9221–9228, https://doi.org/10.1021/ma051591m. I.M.D. Arenaza, E. Meaurio, B. Coto, J.-R. Sarasua, Molecular dynamics modelling for the analysis and prediction of miscibility in polylactide/polyvinilphenol blends, Polymer 51 (2010) 4431–4438, https://doi.org/10.1016/j.polymer.2010.07.018. S. Ishida, R. Nagasaki, K. Chino, T. Dong, Y. Inoue, Toughening of poly(L-lactide) by melt blending with rubbers, J. Appl. Polym. Sci. 113 (2009) 558–566, https://doi. org/10.1002/app.30134. N. Bitinis, R. Verdejo, P. Cassagnau, M. Lopez-Manchado, Structure and properties of polylactide/natural rubber blends, Mater. Chem. Phys. 129 (2011) 823–831, https://doi.org/10.1016/j.matchemphys.2011.05.016. B. Suksut, C. Deeprasertkul, Effect of nucleating agents on physical properties of poly(lactic acid) and its blend with natural rubber, J. Polym. Environ. 19 (2010) 288–296, https://doi.org/10.1007/s10924-010-0278-9. P. Juntuek, C. Ruksakulpiwat, P. Chumsamrong, Y. Ruksakulpiwat, Effect of glycidyl methacrylate-grafted natural rubber on physical properties of polylactic acid and natural rubber blends, J. Appl. Polym. Sci. 125 (2011) 745–754, https://doi.org/ 10.1002/app.36263. M. Kowalczyk, E. Piorkowska, Mechanisms of plastic deformation in biodegradable polylactide/poly(1,4-cis-isoprene) blends, J. Appl. Polym. Sci. 124 (2011) 4579–4589, https://doi.org/10.1002/app.35489. W. Chumeka, V. Tanrattanakul, J.-F. Pilard, P. Pasetto, Effect of poly (vinyl acetate) on mechanical properties and characteristics of poly(lactic acid)/natural rubber blends, J. Polym. Environ. 21 (2012) 450–460, https://doi.org/10.1007/s10924012-0531-5. Y. Huang, C. Zhang, Y. Pan, W. Wang, L. Jiang, Y. Dan, Study on the effect of dicumyl peroxide on structure and properties of poly(lactic acid)/natural rubber blend, J. Polym. Environ. 21 (2012) 375–387, https://doi.org/10.1007/s10924-012-0544-0. W. Chumeka, P. Pasetto, J.-F. Pilard, V. Tanrattanakul, Bio-based triblock copolymers from natural rubber and poly(lactic acid): synthesis and application in polymer blending, Polymer 55 (2014) 4478–4487, https://doi.org/10.1016/j.polymer. 2014.06.091. N.N.B. Mohammad, A. Arsad, A.R. Rahmat, N.S.A. Sani, M.E.A. Mohsin, Influence of compatibilizer on the structure properties of polylactic acid/natural rubber blends, Polym. Sci., Ser. A 58 (2016) 177–185, https://doi.org/10.1134/ s0965545x16020164. C. Pattamaprom, W. Chareonsalung, C. Teerawattananon, S. Ausopron, P. Prachayawasin, P.V. Puyvelde, Improvement in impact resistance of polylactic acid by masticated and compatibilized natural rubber, Iran. Polym. J. 25 (2016) 169–178, https://doi.org/10.1007/s13726-015-0411-7. M. Bijarimi, S. Ahmad, R. Rasid, Mechanical, thermal and morphological properties of poly(lactic acid)/epoxidized natural rubber blends, J. Elastomers Plast. 46 (2012) 338–354, https://doi.org/10.1177/0095244312468442. M. Bijarimi, S. Ahmad, R. Rasid, Melt blends of poly(lactic acid)/natural rubber and liquid epoxidised natural rubber, J. Rubb. Res. 17 (2014) 57–68. N.A. Rosli, I. Ahmad, F.H. Anuar, I. Abdullah, Mechanical and thermal properties of natural rubber-modified poly(lactic acid) compatibilized with telechelic liquid natural rubber, Polym. Test. 54 (2016) 196–202, https://doi.org/10.1016/j. polymertesting.2016.07.021. R. Jaratrotkamjorn, C. Khaokong, V. Tanrattanakul, Toughness enhancement of poly (lactic acid) by melt blending with natural rubber, J. Appl. Polym. Sci. 124 (2011) 5027–5036, https://doi.org/10.1002/app.35617. W.D.N. Ayutthaya, S. Poompradub, Thermal and mechanical properties of poly(lactic acid)/natural rubber blend using epoxidized natural rubber and poly(methyl methacrylate) as co-compatibilizers, Macromol. Res. 22 (2014) 686–692, https:// doi.org/10.1007/s13233-014-2102-1. C. Zhang, W. Wang, Y. Huang, Y. Pan, L. Jiang, Y. Dan, et al., Thermal, mechanical and rheological properties of polylactide toughened by expoxidized natural rubber, Mater. Des. 45 (2013) 198–205, https://doi.org/10.1016/j.matdes. 2012.09.024. M.S.Z.M. Desa, A. Hassan, A. Arsad, R. Arjmandi, N.N.B. Mohammad, Influence of rubber content on mechanical, thermal, and morphological behavior of natural rubber toughened poly(lactic acid)-multiwalled carbon nanotube

[476]

[477]

[478]

[479]

[480]

[481]

[482]

[483]

[484]

[485]

[486]

[487]

[488]

[489]

[490]

[491]

[492]

[493] [494]

[495]

[496]

[497]

[498]

[499]

355

nanocomposites, J. Appl. Polym. Sci. 133 (2016) 44344–44353, https://doi. org/10.1002/app.44344. M. Maroufkhani, A. Katbab, W. Liu, J. Zhang, Polylactide (PLA) and acrylonitrile butadiene rubber (NBR) blends: the effect of ACN content on morphology, compatibility and mechanical properties, Polymer 115 (2017) 37–44, https://doi.org/10. 1016/j.polymer.2017.03.025. Y. Chen, D. Yuan, C. Xu, Dynamically vulcanized biobased polylactide/natural rubber blend material with continuous cross-linked rubber phase, Appl. Mater. Interfaces 6 (2014) 3811–3816, https://doi.org/10.1021/am5004766. D. Yuan, K. Chen, C. Xu, Z. Chen, Y. Chen, Crosslinked bicontinuous biobased PLA/ NR blends via dynamic vulcanization using different curing systems, Carbohydr. Polym. 113 (2014) 438–445, https://doi.org/10.1016/j.carbpol.2014.07.044. C. Xu, D. Yuan, L. Fu, Y. Chen, Physical blend of PLA/NR with co-continuous phase structure: preparation, rheology property, mechanical properties and morphology, Polym. Test. 37 (2014) 94–101, https://doi.org/10.1016/j.polymertesting.2014.05. 005. Y. Chen, K. Chen, Y. Wang, C. Xu, Biobased heat-triggered shape-memory polymers based on polylactide/epoxidized natural rubber blend system fabricated via peroxide-induced dynamic vulcanization: co-continuous phase structure, shape memory behavior, and interfacial compatibilization, Ind. Eng. Chem. Res. 54 (2015) 8723–8731, https://doi.org/10.1021/acs.iecr.5b02195. Y. Wang, K. Chen, C. Xu, Y. Chen, Supertoughened biobased poly(lactic acid)–epoxidized natural rubber thermoplastic vulcanizates: fabrication, co-continuous phase structure, interfacial in situ compatibilization, and toughening mechanism, J. Phys. Chem. B 119 (2015) 12138–12146, https://doi.org/10.1021/acs.jpcb.5b06244. D. Yuan, Z. Chen, K. Chen, W. Mou, Y. Chen, Phenolic resin-induced dynamically vulcanized polylactide/natural rubber blends, Polym.-Plast. Technol. Eng. 55 (2016) 1115–1123, https://doi.org/10.1080/03602559.2015.1132437. H. Zhang, Z. Chen, Z. Zheng, X. Zhu, H. Wang, Shape memory polymer hybrids of SBS/dl-PLA and their shape memory effects, Mater. Chem. Phys. 137 (2013) 750–755, https://doi.org/10.1016/j.matchemphys.2012.10.006. C.-P. Wu, C.-C. Wang, C.-Y. Chen, Enhancing the PLA crystallization rate and mechanical properties by melt blending with poly(styrene-butadiene-styrene) copolymer, Polym. Plast. Test. Technol. 54 (2015) 1043–1050, https://doi.org/10.1080/ 03602559.2014.974274. Y. Wang, Z. Wei, Y. Li, Highly toughened polylactide/epoxidized poly(styrene-bbutadiene-b-styrene) blends with excellent tensile performance, Eur. Polym. J. 85 (2016) 92–104, https://doi.org/10.1016/j.eurpolymj.2016.10.019. C.-H. Tsou, B.-J. Kao, M.-C. Yang, M.-C. Suen, Y.-H. Lee, J.-C. Chen, et al., Biocompatibility and characterization of polylactic acid/styrene-ethylene-butylenestyrene composites, Bio-Med. Mater. Eng. 26 (2015)https://doi.org/10.3233/ bme-151300. V. Sangeetha, T. Varghese, S. Nayak, Toughening of polylactic acid using styrene ethylene butylene styrene: mechanical, thermal, and morphological studies, Polym. Eng. Sci. 56 (2016) 669–675, https://doi.org/10.1002/pen.24293. J. Jiang, L. Su, K. Zhang, G. Wu, Rubber-toughened PLA blends with low thermal expansion, J. Appl. Polym. Sci. 128 (2012) 3993–4000, https://doi.org/10.1002/app. 38642. Q. Zhao, Y. Ding, B. Yang, N. Ning, Q. Fu, Highly efficient toughening effect of ultrafine full-vulcanized powdered rubber on poly(lactic acid)(PLA), Polym. Test. 32 (2013) 299–305, https://doi.org/10.1016/j.polymertesting.2012.11.012. S.-W. Lim, M.-C. Choi, J.-H. Jeong, E.-Y. Park, C.-S. Ha, Toughening poly(lactic acid) (PLA) throughin situreactive blending with liquid polybutadiene rubber (LPB), Compos. Interface 23 (2016) 807–818, https://doi.org/10.1080/09276440.2016. 1175168. P.Y. Vuillaume, A. Vachon, W. Grey, K. Pépin, C.J. Zhang, Compatibilisation of various PLA/thermoplastic elastomer blends with diisocyanate coupling agent, Plast., Rubber Compos. 47 (2018) 95–105, https://doi.org/10.1080/14658011.2018. 1439716. L. Gu, E.E. Nessim, T. Li, C.W. Macosko, Toughening poly(lactic acid) with poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymers, Polymer 156 (2018) 261–269, https://doi.org/10.1016/j.polymer.2018.09.027. Y. Yuan, E. Ruckenstein, Polyurethane toughened polylactide, Polym. Bull. 40 (1998) 485–490, https://doi.org/10.1007/s002890050280. J.-B. Zeng, Y.-D. Li, Y.-S. He, S.-L. Li, Y.-Z. Wang, Improving flexibility of poly(Llactide) by blending with poly(L-lactic acid) based poly(ester-urethane): morphology, mechanical properties, and crystallization behaviors, Ind. Chem. Eng. Res. 50 (2011) 6124–6131, https://doi.org/10.1021/ie102422q. L. Feng, X. Bian, Y. Cui, Z. Chen, G. Li, X. Chen, Flexibility improvement of poly(Llactide) by reactive blending with poly(ether urethane) containing poly(ethylene glycol) blocks, Macromol. Chem. Phys. 214 (2013) 824–834, https://doi.org/10. 1002/macp.201200696. B. Imre, D. Bedő, A. Domján, P. Schön, G.J. Vancso, B. Pukánszky, Structure, properties and interfacial interactions in poly(lactic acid)/polyurethane blends prepared by reactive processing, Eur. Polym. J. 49 (2013) 3104–3113, https://doi.org/10. 1016/j.eurpolymj.2013.07.007. G.-C. Liu, Y.-S. He, J.-B. Zeng, Y. Xu, Y.-Z. Wang, In situ formed crosslinked polyurethane toughened polylactide, Polym. Chem. 5 (2014) 2530–2540, https://doi.org/ 10.1039/c3py01649h. X. Lu, X. Wei, J. Huang, L. Yang, G. Zhang, G. He, et al., Supertoughened poly(lactic acid)/polyurethane blend material by in situ reactive interfacial compatibilization via dynamic vulcanization, Ind. Chem. Eng. Res. 53 (2014) 17386–17393, https:// doi.org/10.1021/ie503092w. Y. Li, H. Shimizu, Toughening of polylactide by melt blending with a biodegradable poly(ether)urethane elastomer, Macromol. Biosci. 7 (2007) 921–928, https://doi. org/10.1002/mabi.200700027.

356

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

[500] F. Feng, L. Ye, Morphologies and mechanical properties of polylactide/thermoplastic polyurethane elastomer blends, J. Appl. Polym. Sci. 119 (2010) 2778–2783, https://doi.org/10.1002/app.32863. [501] F. Feng, X. Zhao, L. Ye, Structure and properties of ultradrawn polylactide/thermoplastic polyurethane elastomer blends, J. Macromol. Sci., Part B: Phys. 50 (2011) 1500–1507, https://doi.org/10.1080/00222348.2010.518889. [502] J.-J. Han, H.-X. Huang, Preparation and characterization of biodegradable polylactide/thermoplastic polyurethane elastomer blends, J. Appl. Polym. Sci. 120 (2011) 3217–3223, https://doi.org/10.1002/app.33338. [503] H. Hong, J. Wei, Y. Yuan, F.-P. Chen, J. Wang, X. Qu, et al., A novel composite coupled hardness with flexibleness-polylactic acid toughen with thermoplastic polyurethane, J. Appl. Polym. Sci. 121 (2011) 855–861, https://doi.org/10.1002/app.33675. [504] V. Jaso, M. Cvetinov, S. Raki, Z.S. Petrovic, Bio-plastics and elastomers from polylactic acid/thermoplastic polyurethane blends, J. Appl. Polym. Sci. 31 (2014) 41104–44112, https://doi.org/10.1002/app.41104. [505] S.K. Dogan, E.A. Reyes, S. Rastogi, G. Ozkoc, Reactive compatibilization of PLA/TPU blends with a diisocyanate, J. Appl. Polym. Sci. 131 (2013) 40251–40259, https:// doi.org/10.1002/app.40251. [506] S.-M. Lai, Y.-C. Lan, W.-L. Wu, Y.-J. Wang, Compatibility improvement of poly(lactic acid)/thermoplastic polyurethane blends with 3-aminopropyl triethoxysilane, J. Appl. Polym. Sci. 132 (2015) 42322–42331, https://doi.org/10.1002/app.42322. [507] F. Zhao, H.-X. Huang, S.-D. Zhang, Largely toughening biodegradable poly(lactic acid)/thermoplastic polyurethane blends by adding MDI, J. Appl. Polym. Sci. 132 (2015) 42511–42520, https://doi.org/10.1002/app.42511. [508] E. Oliaei, B. Kaffashi, S. Davoodi, Investigation of structure and mechanical properties of toughened poly(L-lactide)/thermoplastic poly(ester urethane) blends, J. Appl. Polym. Sci. 133 (2015) 43104–43117, https://doi.org/10.1002/app.43104. [509] S.-M. Lai, Y.-C. Lan, Shape memory properties of melt-blended polylactic acid (PLA)/thermoplastic polyurethane (TPU) bio-based blends, J. Polym. Res. 20 (2013) 140–148, https://doi.org/10.1007/s10965-013-0140-6. [510] J.J. Song, H.H. Chang, H.E. Naguib, Biocompatible shape memory polymer actuators with high force capabilities, Eur. Polym. J. 67 (2015) 186–198, https://doi.org/10. 1016/j.eurpolymj.2015.03.067. [511] V. Jašo, G. Glenn, A. Klamczynski, Z.S. Petrović, Biodegradability study of polylactic acid/thermoplastic polyurethane blends, Polym. Test. 47 (2015) 1–3, https://doi. org/10.1016/j.polymertesting.2015.07.011. [512] T. Whelan, Polymer Technology Dictionary, 1994https://doi.org/10.1007/978-94011-1292-5. [513] H.M. Burt, J.K. Jackson, S.K. Bains, R.T. Liggins, A.M.C. Oktaba, A. Arsenault, et al., Controlled delivery of taxol from microspheres composed of a blend of ethylenevinyl acetate copolymer and poly (D,L-lactic acid), Cancer Lett. 88 (1995) 73–79, https://doi.org/10.1016/0304-3835(94)03614-o. [514] E.-R. Kenawy, G.L. Bowlin, K. Mansfield, J. Layman, D.G. Simpson, E.H. Sanders, et al., Release of tetracycline hydrochloride from electrospun poly(ethylene-covinylacetate), poly(lactic acid), and a blend, J. Control. Release 81 (2002) 57–64, https://doi.org/10.1016/s0168-3659(02)00041-x. [515] J. Yoon, S. Oha, M. Kim, I. China, Y. Kim, Thermal and mechanical properties of poly (L-lactic acid)–poly (ethylene-co-vinyl acetate) blends, Polymer 40 (1999) 2303–2312. [516] X. Liu, L. Lei, J.-W. Hou, M.-F. Tang, S.-R. Guo, Z.-M. Wang, et al., Evaluation of two polymeric blends (EVA/PLA and EVA/PEG) as coating film materials for paclitaxeleluting stent application, J. Mater. Sci. Mater. Med. 22 (2011) 327–337, https://doi. org/10.1007/s10856-010-4213-3. [517] P. Ma, D.G. Hristova-Bogaerds, J.G.P. Goossens, A.B. Spoelstra, Y. Zhang, P.J. Lemstra, Toughening of poly(lactic acid) by ethylene-co-vinyl acetate copolymer with different vinyl acetate content, Eur. Polym. J. 48 (2012) 146–154, https://doi.org/10. 1016/j.eurpolymj.2011.10.015. [518] P. Ma, P. Xu, W. Liu, Y. Zhai, W. Dong, Y. Zhang, et al., Bio-based poly(lactide)/ethylene-co-vinyl acetate thermoplastic vulcanizates by dynamic crosslinking: structure vs. property, RSC Adv. 5 (2015) 15962–15968, https://doi.org/10.1039/ c4ra14194f. [519] P. Xu, P. Ma, M. Hoch, E. Arnoldi, X. Cai, W. Dong, et al., Transparent blown films from poly(lactide) and poly(ethylene-co-vinyl acetate) compounds: structure and property, Polym. Degrad. Stab. 129 (2016) 328–337, https://doi.org/10.1016/ j.polymdegradstab.2016.05.010. [520] N. Zhang, X. Lu, Morphology and properties of super-toughened bio-based poly (lactic acid)/poly(ethylene-co-vinyl acetate) blends by peroxide-induced dynamic vulcanization and interfacial compatibilization, Polym. Test. 56 (2016) 354–363, https://doi.org/10.1016/j.polymertesting.2016.11.003. [521] R.K. Singla, S.N. Maiti, A.K. Ghosh, Fabrication of super tough poly(lactic acid)/ethylene-co-vinyl-acetate blends via a melt recirculation approach: static-short term mechanical and morphological interpretation, RSC Adv. 6 (2016) 14580–14588, https://doi.org/10.1039/c5ra24897c. [522] M. Pracella, M.M.-U. Haque, M. Paci, V. Alvarez, Property tuning of poly(lactic acid)/ cellulose bio-composites through blending with modified ethylene-vinyl acetate copolymer, Carbohydr. Polym. 137 (2016) 515–524, https://doi.org/10.1016/j. carbpol.2015.10.094. [523] X. Shi, Q. Li, A. Zheng, Effects of heat treatment on the damping of EVM/PLA blends modified with polyols, Polym. Test. 35 (2014) 87–91, https://doi.org/10.1016/j. polymertesting.2014.02.008. [524] X. Shi, Q. Li, G. Fu, L. Jia, The effects of a polyol on the damping properties of EVM/ PLA blends, Polym. Test. 33 (2014) 1–6, https://doi.org/10.1016/j.polymertesting. 2013.10.007. [525] X. He, M. Qu, X. Shi, Damping properties of ethylene-vinyl acetate rubber/ polylactic acid blends, J. Mater. Sci. Chem. Eng. 04 (2016) 15–22, https://doi.org/ 10.4236/msce.2016.43003.

[526] X. Shi, L. Jia, Y. Ma, C. Li, Effects of fillers on the damping property of ethylene vinylacetate/polylactic acid blends, J. Mater. Sci. Chem. Eng. 04 (2016) 89–96, https:// doi.org/10.4236/msce.2016.42010. [527] D.V. Cong, T. Hoang, N.V. Giang, N.T. Ha, T.D. Lam, M. Sumita, A novel enzymatic biodegradable route for PLA/EVA blends under agricultural soil of Vietnam, Mater. Sci. Eng. C 32 (2012) 558–563, https://doi.org/10.1016/j.msec.2011.12.012. [528] I. Moura, G. Botelho, A.V. Machado, Characterization of EVA/PLA blends when exposed to different environments, J. Polym. Environ. 22 (2013) 148–157, https:// doi.org/10.1007/s10924-013-0614-y. [529] X. Cao, A. Mohamed, S. Gordon, J. Willett, D. Sessa, DSC study of biodegradable poly (lactic acid) and poly(hydroxy ester ether) blends, Thermochim. Acta 406 (2003) 115–127, https://doi.org/10.1016/s0040-6031(03)00252-1. [530] G. Zhang, J. Zhang, X. Zhou, D. Shen, Miscibility and phase structure of binary blends of polylactide and poly(vinylpyrrolidone), J. Appl. Polym. Sci. 88 (2003) 973–979, https://doi.org/10.1002/app.11735. [531] J.R. Khurma, D.R. Rohindra, R. Devi, Miscibility study of solution cast blends of poly (lactic acid) and poly(vinyl butyral), S. Pac. J. Nat. App. Sci. 23 (2005) 22, https:// doi.org/10.1071/sp05004. [532] A.P.T. Pezzin, G.O.R.A. Ekenstein, C.A.C. Zavaglia, G. Brinke, E.A.R. Duek, Poly(paradioxanone) and poly(l-lactic acid) blends: thermal, mechanical, and morphological properties, J. Appl. Polym. Sci. 88 (2003) 2744–2755. [533] B. Meng, J. Deng, Q. Liu, Z. Wu, W. Yang, Transparent and ductile poly(lactic acid)/ poly(butyl acrylate) (PBA) blends: structure and properties, Eur. Polym. J. 48 (2012) 127–135, https://doi.org/10.1016/j.eurpolymj.2011.10.009. [534] H. Kang, B. Qiao, R. Wang, Z. Wang, L. Zhang, J. Ma, et al., Employing a novel bioelastomer to toughen polylactide, Polymer 54 (2013) 2450–2458, https://doi. org/10.1016/j.polymer.2013.02.053. [535] M. Kowalczyk, E. Piorkowska, S. Dutkiewicz, P. Sowinski, Toughening of polylactide by blending with a novel random aliphatic–aromatic copolyester, Eur. Polym. J. 59 (2014) 59–68, https://doi.org/10.1016/j.eurpolymj.2014.07.002. [536] C.-H. Ho, C.-H. Wang, C.-I. Lin, Y.-D. Lee, Synthesis and characterization of TPO–PLA copolymer and its behavior as compatibilizer for PLA/TPO blends, Polymer 49 (2008) 3902–3910, https://doi.org/10.1016/j.polymer.2008.06.054. [537] H.T. Oyama, Super-tough poly(lactic acid) materials: reactive blending with ethylene copolymer, Polymer 50 (2009) 747–751, https://doi.org/10.1016/j.polymer. 2008.12.025. [538] D. Li, B. Shentu, Z. Weng, Morphology, rheology, and mechanical properties of polylactide/poly(ethylene-co-octene) blends, J. Macromol. Sci., Part B: Phys. 50 (2011) 2050–2059, https://doi.org/10.1080/00222348.2011.557617. [539] Z. Su, Q. Li, Y. Liu, G.-H. Hu, C. Wu, Compatibility and phase structure of binary blends of poly(lactic acid) and glycidyl methacrylate grafted poly(ethylene octane), Eur. Polym. J. 45 (2009) 2428–2433, https://doi.org/10.1016/j.eurpolymj. 2009.04.028. [540] Q. Liu, H. Zhang, M. Zhu, Z. Dong, C. Wu, J. Jiang, et al., Blends of polylactide/ thermoplactic elastomer: miscibility, physical aging and crystallization behaviors, Fiber Polym. 14 (2013) 1688–1698, https://doi.org/10.1007/s12221-013-1688-9. [541] X. Ran, Z. Jia, C. Han, Y. Yang, L. Dong, Thermal and mechanical properties of blends of polylactide and poly(ethylene glycol-co-propylene glycol): influence of annealing, J. Appl. Polym. Sci. 116 (2010) 2050–2057, https://doi. org/10.1002/app.31701. [542] B. Hazer, B.M. Baysal, A.G. Köseoğlu, N. Beşirli, E. Taşkın, Synthesis of polylactide-b-poly (dimethyl siloxane) block copolymers and their blends with pure polylactide, J. Polym. Environ. 20 (2011) 477–484, https://doi.org/ 10.1007/s10924-011-0406-1. [543] P. Xu, P. Ma, X. Cai, S. Song, Y. Zhang, W. Dong, et al., Selectively cross-linked poly (lactide)/ethylene-glycidyl methacrylate-vinyl acetate thermoplastic elastomers with partial dual-continuous network-like structures and shape memory performances, Eur. Polym. J. 84 (2016) 1–12, https://doi.org/10.1016/j.eurpolymj.2016. 09.004. [544] P. Pan, G. Shan, Y. Bao, Enhanced nucleation and crystallization of poly(L-lactic acid) by immiscible blending with poly(vinylidene fluoride), Ind. Eng. Chem. Res. 53 (2014) 3148–3156, https://doi.org/10.1021/ie404085a. [545] R. Salehiyan, S.S. Ray, V. Ojijo, Processing-driven morphology development and crystallization behavior of immiscible polylactide/poly(vinylidene fluoride) blends, Macromol. Mater. Eng. 303 (2018), 1800349. https://doi.org/10.1002/ mame.201800349. [546] W. Dong, H. Wang, F. Ren, J. Zhang, M. He, T. Wu, Y. Li, Dramatic improvement in toughness of PLLA/PVDF blends: the effect of compatibilizer architectures, ACS Sustain. Chem. Eng. 4 (2016) 4480–4489, https://doi.org/10.1021/acssuschemeng. 6b01420. [547] P.H.S. Picciani, E.S. Medeiros, Z. Pan, D.F. Wood, W.J. Orts, L.H.C. Mattoso, B.G. Soares, Structural, electrical, mechanical, and thermal properties of electrospun poly(lactic acid)/polyaniline blend fibers, Macromol. Mater. Eng. 295 (2010) 618–627, https://doi.org/10.1002/mame.201000019. [548] H.-T. Liao, C.-S. Wu, Preparation and characterization of ternary blends composed of polylactide, poly(ɛ-caprolactone) and starch, Mater. Sci. Eng. A 515 (2009) 207–214, https://doi.org/10.1016/j.msea.2009.03.003. [549] V.B. Carmona, A.C. Corrêa, J.M. Marconcini, L.H.C. Mattoso, Properties of a biodegradable ternary blend of thermoplastic starch (TPS), poly(ε-Caprolactone) (PCL) and poly(lactic acid) (PLA), J. Polym. Environ. 23 (2014) 83–89, https://doi.org/ 10.1007/s10924-014-0666-7. [550] V. Mittal, T. Akhtar, N. Matsko, Mechanical, thermal, rheological and morphological properties of binary and ternary blends of PLA, TPS and PCL, Macromol. Mater. Eng. 300 (2015) 423–435, https://doi.org/10.1002/mame.201400332. [551] V. Mittal, T. Akhtar, G. Luckachan, N. Matsko, PLA, TPS and PCL binary and ternary blends: structural characterization and time-dependent morphological changes,

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

[552]

[553]

[554]

[555]

[556]

[557]

[558]

[559]

[560]

[561]

[562]

[563]

[564]

[565]

[566]

[567]

[568]

[569]

[570]

[571]

[572]

[573]

[574]

Colloid Polym. Sci. 293 (2014) 573–585, https://doi.org/10.1007/s00396-0143458-7. S. Davoodi, E. Oliaei, S.M. Davachi, I. Hejazi, J. Seyfi, B.S. Heidari, et al., Correction: preparation and characterization of interface-modified PLA/starch/PCL ternary blends using PLLA/triclosan antibacterial nanoparticles for medical applications, RSC Adv. 6 (2016)https://doi.org/10.1039/c6ra90040b (42611–42611). S.M. Davachi, B.S. Heidari, I. Hejazi, J. Seyfi, E. Oliaei, A. Farzaneh, et al., Interface modified polylactic acid/starch/poly ε-caprolactone antibacterial nanocomposite blends for medical applications, Carbohydr. Polym. 155 (2017) 336–344, https:// doi.org/10.1016/j.carbpol.2016.08.037. J. Wang, W. Zhai, W. Zheng, Poly(ethylene glycol) grafted starch introducing a novel interphase in poly(lactic acid)/poly(ethylene glycol)/starch ternary composites, J. Polym. Environ. 20 (2012) 528–539, https://doi.org/10.1007/s10924-0120416-7. Q. Shi, C. Chen, L. Gao, L. Jiao, H. Xu, W. Guo, Physical and degradation properties of binary or ternary blends composed of poly (lactic acid), thermoplastic starch and GMA grafted POE, Polym. Degrad. Stab. 96 (2011) 175–182, https://doi.org/10. 1016/j.polymdegradstab.2010.10.002. M.M.F. Ferrarezi, M.D.O. Taipina, L.C.E.D. Silva, M.D.C. Gonçalves, Poly(ethylene glycol) as a compatibilizer for poly(lactic acid)/thermoplastic starch blends, J. Polym. Environ. 21 (2012) 151–159, https://doi.org/10.1007/s10924-012-0480-z. Z. Zhen, S. Ying, F. Hongye, R. Jie, R. Tianbin, Preparation, characterization and properties of binary and ternary blends with thermoplastic starch, poly(lactic acid) and poly(butylene succinate), Polym. Renewable Resour. 2 (2011) 49–62, https://doi.org/10.1177/204124791100200201. P. Ma, D.G. Hristova-Bogaerds, P. Schmit, J.G.P. Goossens, P.J. Lemstra, Tailoring the morphology and properties of poly(lactic acid)/poly(ethylene)-co-(vinyl acetate)/ starch blends via reactive compatibilization, Polym. Int. 61 (2012) 1284–1293, https://doi.org/10.1002/pi.4204. L. Zhou, G. Zhao, W. Jiang, Mechanical properties of biodegradable polylactide/poly (ether-block-amide)/thermoplastic starch blends: effect of the crosslinking of starch, J. Appl. Polym. Sci. 133 (2015) 42297, https://doi.org/10.1002/app.42297. T. Kanzawa, K. Tokumitsu, Mechanical properties and morphological changes of poly(lactic acid)/polycarbonate/poly(butylene adipate-co-terephthalate) blend through reactive processing, J. Appl. Polym. Sci. 121 (2011) 2908–2918, https:// doi.org/10.1002/app.33916. R. Chen, M.A. Abdelwahab, M. Misra, A.K. Mohanty, Biobased ternary blends of lignin, poly(lactic acid), and poly(butylene adipate-co-terephthalate): the effect of lignin heterogeneity on blend morphology and compatibility, J. Polym. Environ. 22 (2014) 439–448, https://doi.org/10.1007/s10924-014-0704-5. R. Chen, X. Huang, M. Wang, G. Jin, Evaluation and comparison of mid-infrared, Raman and near-infrared spectroscopies for characterization and determination of the compositions in fully biodegradable poly(lactic acid)/poly(propylene carbonate)/poly(butylene adipate-co-terephthalate) blends combined with chemometrics, J. Macromol. Sci., Part A: Pure Appl. Chem. 53 (2016) 354–361, https://doi.org/10.1080/10601325.2016.1166001. S. Ravati, C. Beaulieu, A.M. Zolali, B.D. Favis, High performance materials based on a self-assembled multiple-percolated ternary blend, AICHE J. 60 (2014) 3005–3012, https://doi.org/10.1002/aic.14495. K. Zhang, A.K. Mohanty, M. Misra, Fully biodegradable and biorenewable ternary blends from polylactide, poly(3-hydroxybutyrate-co-hydroxyvalerate) and poly (butylene succinate) with balanced properties, Appl. Mater. Interfaces 4 (2012) 3091–3101, https://doi.org/10.1021/am3004522. S. Ravati, S. Poulin, K. Piyakis, B.D. Favis, Phase identification and interfacial transitions in ternary polymer blends by ToF-SIMS, Polymer 55 (2014) 6110–6123, https://doi.org/10.1016/j.polymer.2014.09.013. J.-H. Yang, C.-X. Feng, H.-M. Chen, N. Zhang, T. Huang, Y. Wang, Toughening effect of poly(methyl methacrylate) on an immiscible poly(vinylidene fluoride)/ polylactide blend, Polym. Int. 65 (2016) 675–682, https://doi.org/10.1002/pi.5109. A. Auliawan, E.M. Woo, Nanocomposites based on vermiculite clay and ternary blend of poly(L-lactic acid), poly(methyl methacrylate), and poly(ethylene oxide), Polym. Compos. 32 (2011) 1916–1926, https://doi.org/10.1002/pc.21194. A. Auliawan, E.M. Woo, Crystallization kinetics and degradation of nanocomposites based on ternary blend of poly(L-lactic acid), poly(methyl methacrylate), and poly (ethylene oxide) with two different organoclays, J. Appl. Polym. Sci. 125 (2012) https://doi.org/10.1002/app.36761. H. Liu, F. Chen, B. Liu, G. Estep, J. Zhang, Super toughened poly(lactic acid) ternary blends by simultaneous dynamic vulcanization and interfacial compatibilization, Macromolecules 43 (2010) 6058–6066, https://doi.org/10.1021/ma101108g. H. Liu, L. Guo, X. Guo, J. Zhang, Effects of reactive blending temperature on impact toughness of poly(lactic acid) ternary blends, Polymer 53 (2012) 272–276, https:// doi.org/10.1016/j.polymer.2011.12.036. W. Song, H. Liu, F. Chen, J. Zhang, Effects of ionomer characteristics on reactions and properties of poly(lactic acid) ternary blends prepared by reactive blending, Polymer 53 (2012) 2476–2484, https://doi.org/10.1016/j.polymer.2012.03.050. K. Zhang, V. Nagarajan, M. Misra, A.K. Mohanty, Supertoughened renewable PLA reactive multiphase blends system: phase morphology and performance, Appl. Mater. Interfaces 6 (2014) 12436–12448, https://doi.org/10.1021/am502337u. C. Nyambo, M. Misra, A.K. Mohanty, Toughening of brittle poly(lactide) with hyperbranched poly(ester-amide) and isocyanate-terminated prepolymer of polybutadiene, J. Mater. Sci. 47 (2012) 5158–5168, https://doi.org/10.1007/s10853012-6393-3. V.H. Sangeetha, R.B. Valapa, S.K. Nayak, T.O. Varghese, Super toughened renewable poly(lactic acid) based ternary blends system: effect of degree of hydrolysis of ethylene vinyl acetate on impact and thermal properties, RSC Adv. 6 (2016) 72681–72691, https://doi.org/10.1039/c6ra13366e.

357

[575] S. Wang, P. Ma, R. Wang, S. Wang, Y. Zhang, Y. Zhang, Mechanical, thermal and degradation properties of poly( D , L -lactide)/poly(hydroxybutyrate-cohydroxyvalerate)/poly(ethylene glycol) blend, Polym. Degrad. Stab. 93 (2008) 1364–1369, https://doi.org/10.1016/j.polymdegradstab.2008.03.026. [576] K. Hashima, S. Nishitsuji, T. Inoue, Structure-properties of super-tough PLA alloy with excellent heat resistance, Polymer 51 (2010) 3934–3939, https://doi.org/10. 1016/j.polymer.2010.06.045. [577] S. Buddhiranon, N. Kim, T. Kyu, Morphology development in relation to the ternary phase diagram of biodegradable PDLLA/PCL/PEO blends, Macromol. Chem. Phys. 212 (2011) 1379–1391, https://doi.org/10.1002/macp.201100042. [578] W.Z. Ouyang, Y. Huang, H.J. Luo, D.S. Wang, Preparation and properties of poly(lactic acid)/cellulolytic enzyme lignin/PGMA ternary blends, Chin. Chem. Lett. 23 (2012) 351–354, https://doi.org/10.1016/j.cclet.2011.11.023. [579] A.M. Zolali, B.D. Favis, Compatibilization and toughening of co-continuous ternary blends via partially wet droplets at the interface, Polymer 114 (2017) 277–288, https://doi.org/10.1016/j.polymer.2017.02.093. [580] A. Maani, P.J. Carreau, Rheological and morphological properties of thermoplastic olefin blends containing nanosilica, J. Nonnewton Fluid Mech. 233 (2016) 95–106, https://doi.org/10.1016/j.jnnfm.2016.01.017. [581] R. Salehiyan, S.S. Ray, Influence of nanoclay localization on structure-property relationships of polylactide-based biodegradable blend nanocomposites, Macromol. Mater. Eng. 303 (2018), 1800134. https://doi.org/10.1002/mame.201800134. [582] L. Cabedo, J.L. Feijoo, M.P. Villanueva, J.M. Lagarón, E. Giménez, Optimization of biodegradable nanocomposites based on aPLA/PCL blends for food packaging applications, Macromol. Symp. 233 (2006) 191–197, https://doi.org/10.1002/masy. 200690017. [583] R. Salehiyan, K. Hyun, Effect of organoclay on non-linear rheological properties of poly(lactic acid)/poly(caprolactone) blends, Korean J. Chem. Eng. 30 (2013) 1013–1022, https://doi.org/10.1007/s11814-013-0035-6. [584] J. Urquijo, S. Dagréou, G. Guerrica-Echevarría, J.I. Eguiazábal, Structure and properties of poly(lactic acid)/poly(ε-caprolactone) nanocomposites with kinetically induced nanoclay location, J. Appl. Polym. Sci. 133 (2016)https://doi.org/10.1002/ app.43815. [585] J. Ren, Z. Liu, T. Ren, Mechanical and thermal properties of poly(lactid acid)/starch/ montmorillonite biodegradable blends, Polym. Compos. 15 (2007) 633. [586] S. Chapple, R. Anandjiwala, S.S. Ray, Mechanical, thermal, and fire properties of polylactide/starch blend/clay composites, J. Therm. Anal. Calorim. 113 (2012) 703–712, https://doi.org/10.1007/s10973-012-2776-6. [587] M.A. Paglicawan, B.A. Basilia, M.T.V. Navarro, C.S. Emolaga, Influence of nanoclay on the properties of thermoplastic starch/poly(lactic acid) blends, J. Biobaased Mater. Bioenergy 7 (2013) 102–107, https://doi.org/10.1166/jbmb.2013.1276. [588] O.C. Wokadala, S.S. Ray, J. Bandyopadhyay, J. Wesley-Smith, N.M. Emmambux, Morphology, thermal properties and crystallization kinetics of ternary blends of the polylactide and starch biopolymers and nanoclay: the role of nanoclay hydrophobicity, Polymer 71 (2015) 82–92, https://doi.org/10.1016/j.polymer.2015.06. 058. [589] L. Jiang, B. Liu, J. Zhang, Properties of poly(lactic acid)/poly(butylene adipate-coterephthalate)/nanoparticle ternary composites, Ind. Eng. Chem. Res. 48 (2009) 7594–7602, https://doi.org/10.1021/ie900576f. [590] M. Kumar, S. Mohanty, S. Nayak, M.R. Parvaiz, Effect of glycidyl methacrylate (GMA) on the thermal, mechanical and morphological property of biodegradable PLA/PBAT blend and its nanocomposites, Bioresour. Technol. 101 (2010) 8406–8415, https://doi.org/10.1016/j.biortech.2010.05.075. [591] M. Nofar, Synergistic effects of chain extender and nanoclay on the crystallization behavior of polylactide, Int. J. Mater. Sci. Res. 1 (2018) 1–8, https://doi.org/10. 18689/ijmsr-1000101. [592] V. Ojijo, H. Cele, S.S. Ray, Morphology and properties of polymer composites based on biodegradable polylactide/poly[(butylene succinate)-co-adipate] blend and nanoclay, Macromol. Mater. Eng. 296 (2011) 865–877, https://doi.org/10.1002/ mame.201100042. [593] V. Ojijo, T. Malwela, S.S. Ray, R. Sadiku, Unique isothermal crystallization phenomenon in the ternary blends of biopolymers polylactide and poly[(butylene succinate)-co-adipate] and nano-clay, Polymer 53 (2012) 505–518, https://doi.org/10. 1016/j.polymer.2011.12.007. [594] V. Ojijo, S.S. Ray, R. Sadiku, Effect of nanoclay loading on the thermal and mechanical properties of biodegradable polylactide/poly[(butylene succinate)-co-adipate] blend composites, Appl. Mater. Interfaces 4 (2012) 2395–2405, https://doi.org/10. 1021/am201850m. [595] T. Malwela, S.S. Ray, Enzymatic degradation behavior of nanoclay reinforced biodegradable PLA/PBSA blend composites, Int. J. Biol. Macromol. 77 (2015) 131–142, https://doi.org/10.1016/j.ijbiomac.2015.03.018. [596] C. Nuñez, R. Rosales, N. Perera, J.M. Pastor Villarreal, Nanocomposites of PLA/PP blends based on sepiolite, Polym. Bull. 67 (2011) 1991–2016, https://doi.org/10. 1007/s00289-011-0616-7. [597] K. Nuñez, C. Rosales, R. Perera, N. Villarreal, J. Pastor, Poly(lactic acid)/low-density polyethylene blends and its nanocomposites based on sepiolite, Polym. Eng. Sci. 52 (2011) 988–1004, https://doi.org/10.1002/pen.22168. [598] H. Ebadi-Dehaghani, H.A. Khonakdar, M. Barikani, S.H. Jafari, Experimental and theoretical analyses of mechanical properties of PP/PLA/clay nanocomposites, Compos. Part B 69 (2015) 133–144, https://doi.org/10.1016/j.compositesb.2014. 09.006. [599] H. Ebadi-Dehaghani, H.A. Khonakdar, M. Barikani, S.H. Jafari, U. Wagenknecht, G. Heinrich, On localization of clay nanoparticles in polypropylene/poly(lactic acid) blend nanocomposites: correlation with mechanical properties, J. Macromol. Sci., Part B: Phys. 55 (2016) 344–360, https://doi.org/10.1080/00222348.2016. 1151475.

358

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

[600] N. Bitinis, R. Verdejo, E. Maya, E. Espuche, P. Cassagnau, M. Lopez-Manchado, Physicochemical properties of organoclay filled polylactic acid/natural rubber blend bionanocomposites, Compos. Sci. Technol. 72 (2012) 305–313, https://doi.org/10. 1016/j.compscitech.2011.11.018. [601] N. Bitinis, E. Fortunati, R. Verdejo, I. Armentano, L. Torre, J.M. Kenny, et al., Thermal and bio-disintegration properties of poly(lactic acid)/natural rubber/organoclay nanocomposites, App. Cly. Sci. 93–94 (2014) 78–84, https://doi.org/10.1016/j. clay.2014.02.024. [602] N. Bitinis, R. Verdejo, J. Bras, E. Fortunati, J.M. Kenny, L. Torre, et al., Poly(lactic acid)/natural rubber/cellulose nanocrystal bionanocomposites part I. processing and morphology, Carbohydr. Polym. 96 (2013) 611–620, https://doi.org/10.1016/ j.carbpol.2013.02.068. [603] N. Bitinis, E. Fortunati, R. Verdejo, J. Bras, J.M. Kenny, L. Torre, et al., Poly(lactic acid)/natural rubber/cellulose nanocrystal bionanocomposites. Part II: properties evaluation, Carbohydr. Polym. 96 (2013) 621–627, https://doi.org/10.1016/j. carbpol.2013.03.091. [604] H.G. Ock, D.H. Kim, K.H. Ahn, S.J. Lee, J.M. Maia, Effect of organoclay as a compatibilizer in poly(lactic acid) and natural rubber blends, Eur. Polym. J. (2016) 76–216. [605] H.G. Ock, K.H. Ahn, S.J. Lee, K. Hyun, Characterization of compatibilizing effect of organoclay in poly(lactic acid) and natural rubber blends by FT-rheology, Macromolecules 49 (2016) 2832–2842, https://doi.org/10.1021/acs.macromol.5b02157. [606] L. Ashabi, S.H. Jafari, H.A. Khonakdar, R. Boldt, U. Wagenknecht, G. Heinrich, Tuning the processability, morphology and biodegradability of clay incorporated PLA/ LLDPE blends via selective localization of nanoclay induced by melt mixing sequence, Express Polym Lett 7 (2013) 21–39, https://doi.org/10.3144/ expresspolymlett.2013.3. [607] L. Ashabi, S.H. Jafari, H.A. Khonakdar, B. Kretzschmar, U. Wagenknecht, G. Heinrich, Effect of clay type and polymer matrix on microstructure and tensile properties of PLA/LLDPE/clay nanocomposites, J. Appl. Polym. Sci. 130 (2013) 749–758, https:// doi.org/10.1002/app.39209. [608] M.H. Abdolrasouli, H. Nazockdast, G.M.M. Sadeghi, J. Kaschta, Morphology development, melt linear viscoelastic properties and crystallinity of polylactide/polyethylene/organoclay blend nanocomposites, J. Appl. Polym. Sci. 132 (2014), 41300. https://doi.org/10.1002/app.41300. [609] H. Zhao, Z. Cui, X. Wang, L.-S. Turng, X. Peng, Processing and characterization of solid and microcellular poly(lactic acid)/polyhydroxybutyrate-valerate (PLA/ PHBV) blends and PLA/PHBV/Clay nanocomposites, Compos. Part B 51 (2013) 79–91, https://doi.org/10.1016/j.compositesb.2013.02.034. [610] J. Derho, J. Soulestin, P. Krawczak, Structural evolution of poly(lactic acid)/poly (ethylene oxide)/unmodified clay upon ambient ageing, J. Appl. Polym. Sci. 131 (2014), 40426. https://doi.org/10.1002/app.40426. [611] A. Nuzzo, E. Bilotti, T. Peijs, D. Acierno, G. Filippone, Nanoparticle-induced cocontinuity in immiscible polymer blends – a comparative study on bio-based PLA-PA11 blends filled with organoclay, sepiolite, and carbon nanotubes, Polymer 55 (2014) 4908–4919, https://doi.org/10.1016/j.polymer.2014.07.036. [612] B.J. Rashmi, K. Prashantha, M.-F. Lacrampe, P. Krawczak, Toughening of poly(lactic acid) without sacrificing stiffness and strength by melt-blending with polyamide 11 and selective localization of halloysite nanotubes, Express Polym Lett (2016) https://doi.org/10.1063/1.4942284. [613] M.R. Aghjeh, M. Nazari, H.A. Khonakdar, S.H. Jafari, U. Wagenknecht, G. Heinrich, In depth analysis of micro-mechanism of mechanical property alternations in PLA/ EVA/clay nanocomposites: a combined theoretical and experimental approach, Mater. Des. 88 (2015) 1277–1289, https://doi.org/10.1016/j.matdes.2015.09.081. [614] M.R. Aghjeh, V. Asadi, P. Mehdijabbar, H.A. Khonakdar, S.H. Jafari, Application of linear rheology in determination of nanoclay localization in PLA/EVA/Clay nanocomposites: correlation with microstructure and thermal properties, Compos. Part B 86 (2016) 273–284, https://doi.org/10.1016/j.compositesb.2015.09.064. [615] R.K. Singla, S.N. Maiti, A.K. Ghosh, Mechanical, morphological, and solid-state viscoelastic responses of poly(lactic acid)/ethylene-co-vinyl-acetate supertough blend reinforced with halloysite nanotubes, J. Mater. Sci. 51 (2016) 10278–10292, https://doi.org/10.1007/s10853-016-0255-3. [616] E. Oliaei, B. Kaffashi, Investigation on the properties of poly(l-lactide)/thermoplastic poly(ester urethane)/halloysite nanotube composites prepared based on prediction of halloysite nanotube location by measuring free surface energies, Polymer 104 (2016) 104–114, https://doi.org/10.1016/j.polymer.2016.09.092. [617] D. Wu, Y. Zhang, M. Zhang, W. Yu, Selective localization of multiwalled carbon nanotubes in poly(ε-caprolactone)/polylactide blend, Biomacromolecules 10 (2009) 417–424, https://doi.org/10.1021/bm801183f. [618] E. Laredo, M. Grimau, A. Bello, D.F. Wu, Y.S. Zhang, D.P. Lin, AC conductivity of selectively located carbon nanotubes in poly(ε-caprolactone)/polylactide blend nanocomposites, Biomacromolecules 11 (2010) 1339–1347, https://doi.org/10. 1021/bm100135n. [619] Z. Xu, Y. Zhang, Z. Wang, N. Sun, H. Li, Enhancement of electrical conductivity by changing phase morphology for composites consisting of polylactide and poly(εcaprolactone) filled with acid-oxidized multiwalled carbon nanotubes, Appl. Mater. Interfaces 3 (2011) 4858–4864, https://doi.org/10.1021/am201355j. [620] D. Wu, D. Lin, J. Zhang, W. Zhou, M. Zhang, Y. Zhang, et al., Selective localization of nanofillers: effect on morphology and crystallization of PLA/PCL blends, Macromol. Chem. Phys. 212 (2011) 613–626, https://doi.org/10.1002/macp.201000579. [621] S.W. Ko, M.K. Hong, B.J. Park, R.K. Gupta, H.J. Choi, S.N. Bhattacharya, Morphological and rheological characterization of multi-walled carbon nanotube/PLA/PBAT blend nanocomposites, Polym. Bull. 63 (2009) 125–134, https://doi.org/10.1007/s00289009-0072-9. [622] Y. Shi, Y. Li, F. Xiang, T. Huang, C. Chen, Y. Peng, et al., Carbon nanotubes induced microstructure and mechanical properties changes in cocontinuous poly(L-

[623]

[624]

[625]

[626]

[627]

[628]

[629]

[630]

[631]

[632]

[633]

[634]

[635]

[636]

[637]

[638]

[639]

[640]

[641]

[642]

[643]

[644]

[645]

lactide)/ethylene-co-vinyl acetate blends, Polym. Adv. Technol. 23 (2011) 783–790, https://doi.org/10.1002/pat.1959. M. Raja, S.H. Ryu, A. Shanmugharaj, Thermal, mechanical and electroactive shape memory properties of polyurethane (PU)/poly (lactic acid) (PLA)/CNT nanocomposites, Eur. Polym. J. 49 (2013) 3492–3500, https://doi.org/10.1016/j.eurpolymj. 2013.08.009. G. Nasti, G. Gentile, P. Cerruti, C. Carfagna, V. Ambrogi, Double percolation of multiwalled carbon nanotubes in polystyrene/polylactic acid blends, Polymer 99 (2016) 193–203, https://doi.org/10.1016/j.polymer.2016.06.058. T.-W. Lee, Y.G. Jeong, Enhanced electrical conductivity, mechanical modulus, and thermal stability of immiscible polylactide/polypropylene blends by the selective localization of multi-walled carbon nanotubes, Compos. Sci. Technol. 103 (2014) 78–84, https://doi.org/10.1016/j.compscitech.2014.08.019. M.G. Jang, Y.K. Lee, W.N. Kim, Influence of lactic acid-grafted multi-walled carbon nanotube (LA-g-MWCNT) on the electrical and rheological properties of polycarbonate/poly(lactic acid)/LA-g-MWCNT composites, Macromol. Res. 23 (2015) 916–923, https://doi.org/10.1007/s13233-015-3129-7. D.H. Park, T.G. Kan, Y.K. Lee, W.N. Kim, Effect of multi-walled carbon nanotube dispersion on the electrical and rheological properties of poly(propylene carbonate)/ poly(lactic acid)/multi-walled carbon nanotube composites, J. Mater. Sci. 48 (2012) 481–488, https://doi.org/10.1007/s10853-012-6762-y. M. Arrieta, E. Fortunati, F. Dominici, E. Rayón, J. López, J. Kenny, PLA-PHB/cellulose based films: mechanical, barrier and disintegration properties, Polym. Degrad. Stab. 107 (2014) 139–149, https://doi.org/10.1016/j.polymdegradstab.2014.05. 010. M. Arrieta, E. Fortunati, F. Dominici, E. Rayón, J. López, J. Kenny, Multifunctional PLA–PHB/cellulose nanocrystal films: processing, structural and thermal properties, Carbohydr. Polym. 107 (2014) 16–24, https://doi.org/10.1016/j.carbpol.2014. 02.044. Arrieta, E. Fortunati, F. Dominici, J. López, J. Kenny, Bionanocomposite films based on plasticized PLA–PHB/cellulose nanocrystal blends, Carbohydr. Polym. 121 (2015) 265–275, https://doi.org/10.1016/j.carbpol.2014.12.056. M. Arrieta, J. López, D. López, J. Kenny, L. Peponi, Biodegradable electrospun bionanocomposite fibers based on plasticized PLA–PHB blends reinforced with cellulose nanocrystals, Ind. Crop. Prod. 93 (2016) 290–301, https://doi.org/10.1016/j. indcrop.2015.12.058. F. Luzi, E. Fortunati, A. Jiménez, D. Puglia, D. Pezzolla, G. Gigliotti, et al., Production and characterization of PLA_PBS biodegradable blends reinforced with cellulose nanocrystals extracted from hemp fibres, Ind. Crop. Prod. 93 (2016) 276–289, https://doi.org/10.1016/j.indcrop.2016.01.045. X. Zhang, Y. Zhang, Reinforcement effect of poly(butylene succinate) (PBS)-grafted cellulose nanocrystal on toughened PBS/polylactic acid blends, Carbohydr. Polym. 140 (2016) 374–382, https://doi.org/10.1016/j.carbpol.2015.12.073. M. Pracella, M.M.-U. Haque, D. Puglia, Morphology and properties tuning of PLA/ cellulose nanocrystals bio-nanocomposites by means of reactive functionalization and blending with PVAc, Polymer 55 (2014) 3720–3728, https://doi.org/10.1016/ j.polymer.2014.06.071. V. Heshmati, M.R. Kamal, B.D. Favis, Cellulose nanocrystal in poly(lactic acid)/polyamide11 blends: preparation, morphology and co-continuity, Eur. Polym. J. 98 (2018) 11–20, https://doi.org/10.1016/j.eurpolymj.2017.10.027. V. Heshmati, M.R. Kamal, B.D. Favis, Tuning the localization of finely dispersed cellulose nanocrystal in poly (lactic acid)/bio-polyamide11 blends, J. Polym. Sci. B Polym. Phys. 56 (2017) 576–587, https://doi.org/10.1002/polb.24563. Y. Shen, T.-T. Zhang, J.-H. Yang, N. Zhang, T. Huang, Y. Wang, Selective localization of reduced graphene oxides at the interface of PLA/EVA blend and its resultant electrical resistivity, Polym. Compos. 38 (2015) 1982–1991, https://doi.org/10. 1002/pc.23769. M. Forouharshad, L. Gardella, D. Furfaro, M. Galimberti, O. Monticelli, A lowenvironmental-impact approach for novel bio-composites based on PLLA/PCL blends and high surface area graphite, Eur. Polym. J. 70 (2015) 28–36, https:// doi.org/10.1016/j.eurpolymj.2015.06.016. I. Kelnar, J. Kratochvíl, L. Kaprálková, A. Zhigunov, M. Nevoralová, Graphite nanoplatelets-modified PLA/PCL: effect of blend ratio and nanofiller localization on structure and properties, J. Mech. Behav. Biomed. Mater. 71 (2017) 271–278, https://doi.org/10.1016/j.jmbbm.2017.03.028. O.J. Botlhoko, J. Ramontja, S.S. Ray, Thermal, mechanical, and rheological properties of graphite- and graphene oxide-filled biodegradable polylactide/poly(ɛcaprolactone) blend composites, J. Appl. Polym. Sci. 134 (2017), 45373. https:// doi.org/10.1002/app.45373. O.J. Botlhoko, J. Ramontja, S.S. Ray, Morphological development and enhancement of thermal, mechanical, and electronic properties of thermally exfoliated graphene oxide-filled biodegradable polylactide/poly(ε-caprolactone) blend composites, Polymer 139 (2018) 188–200, https://doi.org/10.1016/j.polymer.2018.02.005. W. Wu, C. Wu, H. Peng, Q. Sun, L. Zhou, J. Zhuang, et al., Effect of nitrogen-doped graphene on morphology and properties of immiscible poly(butylene succinate)/ polylactide blends, Compos. Part B 113 (2017) 300–307, https://doi.org/10.1016/ j.compositesb.2017.01.037. D. Li, B. Shentu, Z. Weng, Preparation and properties of polylactide/poly(ethyleneco-octene)/nano-SiO2 ternary composites, J. Macromol. Sci., Part B: Phys. 51 (2012) 1766–1775, https://doi.org/10.1080/00222348.2012.659633. F. Yu, H.-X. Huang, Simultaneously toughening and reinforcing poly(lactic acid)/ thermoplastic polyurethane blend via enhancing interfacial adhesion by hydrophobic silica nanoparticles, Polym. Test. 45 (2015) 107–113, https://doi.org/10. 1016/j.polymertesting.2015.06.001. H. Xiu, C. Huang, H. Bai, J. Jiang, F. Chen, H. Deng, et al., Improving impact toughness of polylactide/poly(ether)urethane blends via designing the phase morphology

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

[646]

[647]

[648]

[649]

[650]

[651]

[652]

[653]

[654]

[655]

[656]

[657]

[658] [659]

[660]

[661]

[662]

[663]

[664]

[665]

[666]

[667] [668]

[669]

[670]

assisted by hydrophilic silica nanoparticles, Polymer 55 (2014) 1593–1600, https://doi.org/10.1016/j.polymer.2014.01.057. D. Vrsaljko, D. Macut, V. Kovačević, Potential role of nanofillers as compatibilizers in immiscible PLA/LDPE Blends, J. Appl. Polym. Sci. 132 (2014)https://doi.org/10. 1002/app.41414. E.J. Dil, B.D. Favis, Localization of micro and nano- silica particles in a high interfacial tension poly(lactic acid)/low density polyethylene system, Polymer 77 (2015) 156–166, https://doi.org/10.1016/j.polymer.2015.08.063. E.J. Dil, N. Virgilio, B.D. Favis, The effect of the interfacial assembly of nano-silica in poly(lactic acid)/poly(butylene adipate-co-terephthalate) blends on morphology, rheology and mechanical properties, Eur. Polym. J. 85 (2016) 635–646, https:// doi.org/10.1016/j.eurpolymj.2016.07.022. X. Hao, J. Kaschta, Y. Pan, X. Liu, D.W. Schubert, Intermolecular cooperativity and entanglement network in a miscible PLA/PMMA blend in the presence of nanosilica, Polymer 82 (2016) 57–65, https://doi.org/10.1016/j.polymer.2015.11. 029. H. Xiu, H.W. Bai, C.M. Huang, C.L. Xu, X.Y. Li, Q. Fu, Selective localization of titanium dioxide nanoparticles at the interface and its effect on the impact toughness of poly (L-lactide)/poly(ether)urethane blends, Express Polym Lett 7 (2013) 261–271, https://doi.org/10.3144/expresspolymlett.2013.24. J. Mofokeng, A. Luyt, Morphology and thermal degradation studies of melt-mixed poly(lactic acid) (PLA)/poly(ε-caprolactone) (PCL) biodegradable polymer blend nanocomposites with TiO2 as filler, Polym. Test. 45 (2015) 93–100, https://doi. org/10.1016/j.polymertesting.2015.05.007. S.C. Agwuncha, S.S. Ray, J. Jayaramudu, C. Khoathane, R. Sadiku, Influence of boehmite nanoparticle loading on the mechanical, thermal, and rheological properties of biodegradable polylactide/poly(ϵ-caprolactone) blends, Macromol. Mater. Eng. 300 (2014) 31–47, https://doi.org/10.1002/mame.201400212. E.J. Dil, M. Arjmand, Y. Li, U. Sundararaj, B.D. Favis, Assembling copper nanowires at the interface and in discrete phases in PLA-based polymer blends, Eur. Polym. J. 85 (2016) 187–197, https://doi.org/10.1016/j.eurpolymj.2016.09.053. R. Grande, A.J.F. Carvalho, Compatible ternary blends of chitosan/poly(vinyl alcohol)/poly(lactic acid) produced by oil-in-water emulsion processing, Biomacromolecules 12 (2011) 907–914, https://doi.org/10.1021/bm101227q. R. Zhang, W. Xu, F. Jiang, Fabrication and characterization of dense chitosan/ polyvinyl-alcohol/poly-lactic-acid blend membranes, Fiber Polym. 13 (2012) 571–575, https://doi.org/10.1007/s12221-012-0571-4. Z. Zakaria, M.S. Islam, A. Hassan, M.K.M. Haafiz, R. Arjmandi, I.M. Inuwa, M. Hasan, Mechanical properties and morphological characterization of PLA/chitosan/epoxidized natural rubber composites, Adv. Mater. Sci. Eng. 3 (2013)https://doi.org/10. 1155/2013/6290. M. Arrieta, J. López, D. López, J. Kenny, L. Peponi, Effect of chitosan and catechin addition on the structural, thermal, mechanical and disintegration properties of plasticized electrospun PLA-PHB biocomposites, Polym. Degrad. Stab. 132 (2016) 145–156, https://doi.org/10.1016/j.polymdegradstab.2016.02.027. M. Nofar, C.B. Park, Polylactide Foams: Fundamentals, Manufacturing and Applications, 1st edition Elsevier, 2017 (ISBN: 978-0-12-813991-2). M. Nofar, Effects of nano-/micro-sized additives and the corresponding induced crystallinity on the extrusion foaming behavior of PLA using supercritical CO 2 , Mater. Des. 101 (2016) 24–34, https://doi.org/10.1016/j.matdes. 2016.03.147. M. Keshtkar, M. Nofar, C. Park, P. Carreau, Extruded PLA/clay nanocomposite foams blown with supercritical CO2, Polymer 55 (2014) 4077–4090, https://doi.org/10. 1016/j.polymer.2014.06.059. A. Ameli, D. Jahani, M. Nofar, P.U. Jung, C.B. Park, Processing and characterization of solid and foamed injection-molded polylactide with talc, J. Cell. Plast. 49 (2013) 351–374, https://doi.org/10.1177/0021955x13481993. A. Ameli, D. Jahani, M. Nofar, P. Jung, C. Park, Development of high void fraction polylactide composite foams using injection molding: mechanical and thermal insulation properties, Compos. Sci. Technol. 90 (2014) 88–95, https://doi.org/10. 1016/j.compscitech.2013.10.019. A. Ameli, M. Nofar, D. Jahani, G. Rizvi, C. Park, Development of high void fraction polylactide composite foams using injection molding: crystallization and foaming behaviors, Chem. Eng. 262 (2015) 78–87, https://doi.org/10.1016/j.cej.2014.09. 087. N. Najafi, M.-C. Heuzey, P.J. Carreau, D. Therriault, C.B. Park, Mechanical and morphological properties of injection molded linear and branched-polylactide (PLA) nanocomposite foams, Eur. Polym. J. 73 (2015) 455–465, https://doi.org/10.1016/ j.eurpolymj.2015.11.003. M. Nofar, A. Ameli, C.B. Park, Development of polylactide bead foam with double crystal melting peak structure, Polymer 69 (2015) 83–94, https://doi.org/10. 1016/j.polymer.2015.05.048. M. Nofar, A. Ameli, C.B. Park, A novel technology to manufacture biodegradable polylactide bead foam products, Mater. Des. 83 (2015) 413–421, https://doi.org/ 10.1016/j.matdes.2015.06.052. Park CB, Nofar M. A method for the preparation of PLA bead foams. Int Appl Patent No: PCT/NL2013/050231, WO 2014158014 A1 (US 20160039990 A1). M. Nofar, W. Zhu, C. Park, Effect of dissolved CO2 on the crystallization behavior of linear and branched PLA, Polymer 53 (2012) 3341–3353, https://doi.org/10.1016/j. polymer.2012.04.054. M. Nofar, A. Tabatabaei, A. Ameli, C.B. Park, Comparison of melting and crystallization behaviors of polylactide under high-pressure CO2, N2, and He, Polymer (2014) https://doi.org/10.1063/1.4873791. M. Nofar, A. Ameli, C.B. Park, The thermal behavior of polylactide with different Dlactide content in the presence of dissolved CO2, Macromol. Mater. Eng. 299 (2014) 1232–1239, https://doi.org/10.1002/mame.201300474.

359

[671] M. Nofar, A. Tabatabaei, C.B. Park, Effects of nano-/micro-sized additives on the crystallization behaviors of PLA and PLA/CO2 mixtures, Polymer 54 (2013) 2382–2391, https://doi.org/10.1016/j.polymer.2013.02.049. [672] N. Najafi, M.-C. Heuzey, P.J. Carreau, D. Therriault, C.B. Park, Rheological and foaming behavior of linear and branched polylactides, Rheol. Acta 53 (2014) 779–790, https://doi.org/10.1007/s00397-014-0801-3. [673] M. Nofar, W. Zhu, C.B. Park, J. Randall, Crystallization kinetics of linear and longchain-branched polylactide, Ind. Eng. Chem. Res. 50 (2011) 13789–13798, https://doi.org/10.1021/ie2011966. [674] J. Wang, W. Zhu, H. Zhang, C.B. Park, Continuous processing of low-density, microcellular poly(lactic acid) foams with controlled cell morphology and crystallinity, Chem. Eng. Sci. 75 (2012) 390–399, https://doi.org/10.1016/j.ces.2012.02. 051. [675] M. Nofar, Rheological, thermal, and foaming behaviors of different polylactide grades, Int. J. Mater. Sci. Res. 1 (1) (2018) 16–22, https://doi.org/10.18689/ijmsr1000103. [676] X. Liao, A.V. Nawaby, Solvent free generation of open and skinless foam in poly(Llactic acid)/poly(D,L-lactic acid) blends using carbon dioxide, Ind. Eng. Chem. Res. 51 (2012) 6722–6730, https://doi.org/10.1021/ie3000997. [677] F.C. Pavia, V.L. Carrubba, V. Brucato, Polymeric scaffolds based on blends of poly-Llactic acid (PLLA) with poly-D-L-lactic acid (PLA) prepared via thermally induced phase separation (TIPS): demixing conditions and morphology, Polym. Bull. 70 (2012) 563–578, https://doi.org/10.1007/s00289-012-0861-4. [678] P. Jia, J. Hu, W. Zhai, Y. Duan, J. Zhang, C. Han, Cell morphology and improved heat resistance of microcellular poly(l-lactide) foam via introducing stereocomplex crystallites of PLA, Ind. Eng. Chem. Res. 54 (2015) 2476–2488, https://doi.org/10. 1021/ie504345y. [679] L. Wang, R.E. Lee, G. Wang, R.K. Chu, J. Zhao, C.B. Park, Use of stereocomplex crystallites for fully-biobased microcellular low-density poly(lactic acid) foams for green packaging, Chem. Eng. 327 (2017) 1151–1162, https://doi.org/10.1016/j. cej.2017.07.024. [680] D. Preechawong, M. Peesan, P. Supaphol, R. Rujiravanit, Preparation and characterization of starch/poly(L-lactic acid) hybrid foams, Carbohydr. Polym. 59 (2005) 329–337, https://doi.org/10.1016/j.carbpol.2004.10.003. [681] M. Mihai, M.A. Huneault, B.D. Favis, H. Li, Extrusion foaming of semi-crystalline PLA and PLA/thermoplastic starch blends, Macromol. Biosci. 7 (2007) 907–920, https:// doi.org/10.1002/mabi.200700080. [682] J.-F. Zhang, X. Sun, Biodegradable foams of poly(lactic acid)/starch. I. Extrusion condition and cellular size distribution, J. Appl. Polym. Sci. 106 (2007) 857–862, https://doi.org/10.1002/app.26715. [683] J.-F. Zhang, X. Sun, Biodegradable foams of poly(lactic acid)/starch. II. Cellular structure and water resistance, J. Appl. Polym. Sci. 106 (2007) 3058–3062, https://doi.org/10.1002/app.26697. [684] A. Hao, Y. Geng, Q. Xu, Z. Lu, L. Yu, Study of different effects on foaming process of biodegradable PLA/starch composites in supercritical/compressed carbon dioxide, J. Appl. Polym. Sci. 109 (2008) 2679–2686, https://doi.org/10.1002/ app.27861. [685] S.-Y. Lee, M.A. Hanna, Preparation and characterization of tapioca starch-poly(lactic acid)-Cloisite NA nanocomposite foams, J. Appl. Polym. Sci. 110 (2008) 2337–2344, https://doi.org/10.1002/app.27730. [686] S.Y. Lee, M.A. Hanna, Tapioca starch-poly(lactic acid)-Cloisite 30B nanocomposite foams, Polym. Compos. 30 (2009) 665–672, https://doi.org/10.1002/ pc.20664. [687] E.D.M. Teixeira, A.D. Campos, J.M. Marconcini, T.J. Bondancia, D. Wood, A. Klamczynski, et al., Starch/fiber/poly(lactic acid) foam and compressed foam composites, RSC Adv. 4 (2014) 6616, https://doi.org/10.1039/c3ra47395c. [688] H. Yuan, Z. Liu, J. Ren, Preparation, characterization, and foaming behavior of poly (lactic acid)/poly(butylene adipate-co-butylene terephthalate) blend, Polym. Eng. Sci. 49 (2009) 1004–1012, https://doi.org/10.1002/pen.21287. [689] S. Pilla, S.G. Kim, G.K. Auer, S. Gong, C.B. Park, Microcellular extrusion foaming of poly(lactide)/poly(butylene adipate-co-terephthalate) blends, Mater. Sci. Eng. C 30 (2010) 255–262, https://doi.org/10.1016/j.msec.2009.10.010. [690] K. Li, Z. Cui, X. Sun, L.-S. Turng, H. Huang, Effects of nanoclay on the morphology and physical properties of solid and microcellular injection molded polyactide/ poly(butylenes adipate-co-terephthalate) (PLA/PBAT) nanocomposites and blends, J. Biobaased Mater. Bioenergy 5 (2011) 442–451, https://doi.org/10.1166/ jbmb.2011.1182. [691] X. Shi, G. Zhang, Y. Liu, Z. Ma, Z. Jing, X. Fan, Microcellular foaming of polylactide and poly(butylene adipate-co-terphathalate) blends and their CaCO3 reinforced nanocomposites using supercritical carbon dioxide, Polym. Adv. Technol. 27 (2016) 550–560, https://doi.org/10.1002/pat.3768. [692] R. Zhang, C. Cai, Q. Liu, S. Hu, Enhancing the melt strength of poly(lactic acid) via microcrosslinking and blending with poly (butylene adipate-co-butylene terephthalate) for the preparation of foam, J. Polym. Environ. 25 (2017) 1335–1341. [693] Kang, P. Chen, X. Shi, G. Zhang, C. Wang, Preparation of open-porous stereocomplex PLA/PBAT scaffolds and correlation between their morphology, mechanical behavior, and cell compatibility, RSC Adv. 8 (2018) 12933–12943, https://doi.org/10.1039/c8ra01305e. [694] X. Shi, J. Qin, L. Wang, L. Ren, F. Rong, D. Li, et al., Introduction of stereocomplex crystallites of PLA for the solid and microcellular poly(lactide)/poly(butylene adipate-co-terephthalate) blends, RSC Adv. 8 (2018) 11850–11861, https://doi. org/10.1039/c8ra01570h. [695] H.B. Zhao, Z. Cui, X. Sun, L.-S. Turng, X. Peng, Morphology and properties of injection molded solid and microcellular polylactic acid/polyhydroxybutyrate-valerate (PLA/PHBV) blends, Ind. Eng. Chem. Res. 52 (2013) 2569–2581, https://doi.org/ 10.1021/ie301573y.

360

M. Nofar et al. / International Journal of Biological Macromolecules 125 (2019) 307–360

[696] Q. Guan, H.E. Naguib, Fabrication and characterization of PLA/PHBV-chitin nanocomposites and their foams, J. Polym. Environ. 22 (2013) 119–130, https://doi. org/10.1007/s10924-013-0625-8. [697] C. Ji, N. Annabi, M. Hosseinkhani, S. Sivaloganathan, F. Dehghani, Fabrication of poly-DL-lactide/polyethylene glycol scaffolds using the gas foaming technique, Acta Biomater. 8 (2012) 570–578, https://doi.org/10.1016/j.actbio.2011.09.028. [698] W. Zhang, B. Chen, H. Zhao, P. Yu, D. Fu, J. Wen, et al., Processing and characterization of supercritical CO2 batch foamed poly(lactic acid)/poly(ethylene glycol) scaffold for tissue engineering application, J. Appl. Polym. Sci. 130 (2013) 3066–3073, https://doi.org/10.1002/app.39523. [699] B. Chen, X. Jing, H. Mi, H. Zhao, W. Zhang, X. Peng, L. Turng, Fabrication of polylactic acid/polyethylene glycol (PLA/PEG) porous scaffold by supercritical CO2 foaming and particle leaching, Polym. Eng. Sci. 55 (2015) 1339–1348, https://doi.org/10. 1002/pen.24073. [700] X. Wang, W. Liu, H. Zhou, B. Liu, H. Li, Z. Du, et al., Study on the effect of dispersion phase morphology on porous structure of poly (lactic acid)/poly (ethylene terephthalate glycol-modified) blending foams, Polymer 54 (2013) 5839–5851, https://doi.org/10.1016/j.polymer.2013.08.050. [701] P. Ma, X. Wang, B. Liu, Y. Li, S. Chen, Y. Zhang, et al., Preparation and foaming extrusion behavior of polylactide acid/polybutylene succinate/montmorillonoid nanocomposite, J. Cell. Plast. 48 (2012) 191–205, https://doi.org/10.1177/ 0021955x11434182. [702] J. Zhou, Z. Yao, C. Zhou, D. Wei, S. Li, Mechanical properties of PLA/PBS foamed composites reinforced by organophilic montmorillonite, J. Appl. Polym. Sci. 131 (2014)https://doi.org/10.1002/app.40773. [703] P. Yu, H. Mi, A. Huang, L. Geng, B. Chen, T. Kuang, W. Mou, X. Peng, Effect of poly (butylenes succinate) on poly(lactic acid) foaming behavior: formation of open cell structure, Ind. Eng. Chem. Res. 54 (2015) 6199–6207, https://doi.org/10. 1021/acs.iecr.5b00477. [704] X. Shi, L. Wang, Y. Kang, J. Qin, J. Li, H. Zhang, et al., Effect of poly(butylenes succinate) on the microcellular foaming of polylactide using supercritical carbon dioxide, J. Polym. Res. 25 (2018), 229. https://doi.org/10.1007/s10965-018-1620-5. [705] H. Zhao, G. Zhao, Mechanical and thermal properties of conventional and microcellular injection molded poly (lactic acid)/poly (ε-caprolactone) blends, J. Mech. Behav. Biomed. Mater. 53 (2016) 59–67, https://doi.org/10.1016/j.jmbbm. 2015.08.002. [706] H. Zhao, X. Yan, G. Zhao, Z. Guo, Microcellular injection molded polylactic acid/poly (ε-caprolactone) blends with supercritical CO2: correlation between rheological properties and their foaming behavior, Polym. Eng. Sci. 56 (2016) 939–946, https://doi.org/10.1002/pen.24323. [707] Z. Lv, N. Zhao, Z. Wu, C. Zhu, Q. Li, Fabrication of novel open-cell foams of poly(εcaprolactone)/poly(lactic acid) blends for tissue-engineering scaffolds, Ind. Eng. Chem. Res. 57 (2018) 12951–12958, https://doi.org/10.1021/acs.iecr.8b02233. [708] S. Pradeep, H. Kharbas, L.-S. Turng, A. Avalos, J. Lawrence, S. Pilla, Investigation of thermal and thermomechanical properties of biodegradable PLA/PBSA composites processed via supercritical fluid-assisted foam injection molding, Polymers 9 (2017) 22–39, https://doi.org/10.3390/polym9010022. [709] A. Kramschuster, L.-S. Turng, An injection molding process for manufacturing highly porous and interconnected biodegradable polymer matrices for use as tissue engineering scaffolds, J. Biomed. Mater. Res. B Appl. Biomater. 9999B (92) (2009) 366–441, https://doi.org/10.1002/jbm.b.31523. [710] B. Yao, A.V. Nawaby, X. Liao, R. Burk, Physical characteristics of PLLA/PMMA blends and their CO2 blowing foams, J. Cell. Plast. 43 (2007) 385–398, https://doi.org/10. 1177/0021955x07079209.

[711] D. Velasco, L. Benito, M. Fernández-Gutiérrez, J.S. Román, C. Elvira, Preparation in supercritical CO2 of porous poly(methyl methacrylate)–poly(L-lactic acid) (PMMA–PLA) scaffolds incorporating ibuprofen, J. Supercrit. Fluids 54 (2010) 335–341, https://doi.org/10.1016/j.supflu.2010.05.012. [712] D. Kohlhoff, M. Ohshima, Open cell microcellular foams of polylactic acid (PLA)based blends with semi-interpenetrating polymer networks, Macromol. Mater. Eng. 296 (2011) 770–777, https://doi.org/10.1002/mame.201000371. [713] C. Zhou, L. Ma, W. Li, D. Yao, Fabrication of tissue engineering scaffolds through solid-state foaming of immiscible polymer blends, Biofabrication 3 (2011), 045003. https://doi.org/10.1088/1758-5082/3/4/045003. [714] X. Liao, H. Zhang, Y. Wang, L. Wu, G. Li, Unique interfacial and confined porous morphology of PLA/PS blends in supercritical carbon dioxide, RSC Adv. 4 (2014) 45109–45117, https://doi.org/10.1039/c4ra07592g. [715] L. Tang, W. Zhai, W. Zheng, Autoclave preparation of expanded polypropylene/poly (lactic acid) blend bead foams with a batch foaming process, J. Cell. Plast. 47 (2011) 429–446, https://doi.org/10.1177/0021955x11406004. [716] D. Bao, X. Liao, T. He, Q. Yang, G. Li, Preparation of nanocellular foams from polycarbonate/poly(lactic acid) blend by using supercritical carbon dioxide, J. Polym. Res. 20 (2013)https://doi.org/10.1007/s10965-013-0290-6. [717] Y. Yoon, C.J.G. Plummer, J.-A.E. Månson, Solid heat-expandable polylactide-poly (methyl methacrylate) foam precursors prepared by immersion in liquid carbon dioxide, J. Mater. Sci. 50 (2015) 7208–7217, https://doi.org/10.1007/s10853-0159275-7. [718] M. Zhao, X. Ding, J. Mi, H. Zhou, X. Wang, Role of high-density polyethylene in the crystallization behaviors, rheological property, and supercritical CO2 foaming of poly (lactic acid), Polym. Degrad. Stab. 146 (2017) 277–286, https://doi.org/10. 1016/j.polymdegradstab.2017.11.003. [719] H. Zhou, M. Zhao, Z. Qu, J. Mi, X. Wang, Y. Deng, Thermal and rheological properties of poly(lactic acid)/low-density polyethylene blends and their supercritical CO2 foaming behavior, J. Polym. Environ. 26 (2018) 3564–3573, https://doi.org/10. 1007/s10924-018-1240-5. [720] H. Mi, M.R. Salick, X. Jing, B.R. Jacques, W.C. Crone, X. Peng, L. Turng, Characterization of thermoplastic polyurethane/polylactic acid (TPU/PLA) tissue engineering scaffolds fabricated by microcellular injection molding, Mater. Sci. Eng. C 33 (2013) 4767, https://doi.org/10.1016/j.msec.2013.07.037. [721] M. Barmouz, A.H. Behravesh, Statistical and experimental investigation on low density microcellular foaming of PLA-TPU/cellulose nano-fiber bionanocomposites, Polym. Test. 61 (2017) 300–313, https://doi.org/10.1016/j. polymertesting.2017.05.032. [722] M. Barmouz, A.H. Behravesh, Foaming and thermal characteristics of bio-based polylactic acid–thermoplastic polyurethane blends, J. Cell. Plast. 54 (2018) 931–955, https://doi.org/10.1177/0021955x18793841. [723] J.J. Song, H.H. Chang, H.E. Naguib, Design and characterization of biocompatible shape memory polymer (SMP) blend foams with a dynamic porous structure, Polymer 56 (2015) 82–92, https://doi.org/10.1016/j.polymer.2014.09.062. [724] L. Jia, G. Fu, X. Shi, Foaming and damping properties of ethylene vinyl-acetate copolymer/polylactic acid blends, J. Macromol. Sci., Part B: Phys. 54 (2015) 190–202, https://doi.org/10.1080/00222348.2014.998556. [725] D.-H. Han, M.-C. Choi, J.-H. Jeong, K.-M. Choi, H.-S. Kim, Properties of acrylonitrile butadiene rubber (NBR)/poly(lactic acid) (PLA) blends and their foams, Compos. Interfaces 23 (2016) 771–780, https://doi.org/10.1080/09276440.2016.1170518.