Effect of chitosan and catechin addition on the structural, thermal, mechanical and disintegration properties of plasticized electrospun PLA-PHB biocomposites

Polymer Degradation and Stability xxx (2016) 1e12

Contents lists available at ScienceDirect

Polymer Degradation and Stability journal homepage: www.elsevier.com/locate/polydegstab

Effect of chitosan and catechin addition on the structural, thermal, mechanical and disintegration properties of plasticized electrospun PLA-PHB biocomposites
pez b, D. Lo
pez a, J.M. Kenny a, L. Peponi a, ** M.P. Arrieta a, *, J. Lo a b

Institute of Polymer Science and Technology, ICTP-CSIC, Madrid, Spain Instituto de Tecnología de Materiales, Universitat Polit ecnica de Valencia, Alcoy-Alicante, Spain

a r t i c l e i n f o

a b s t r a c t

Article history: Received 24 November 2015 Received in revised form 18 January 2016 Accepted 25 February 2016 Available online xxx

In this paper the processing and properties of flexible electrospun biocomposites based on poly(lactic acid) (PLA) blended with 25 wt% of poly(hydroxybutyrate) (PHB), plasticized with 15 wt% of acetyl(tributyl citrate) (ATBC) and further loaded with 1 wt% and 5 wt% of chitosan (Ch) or catechin (Cat) microparticles are reported. Both fillers present a high content of hydroxyl groups on their surfaces. The morphological, structural, thermal and mechanical performance of electrospun biocomposites was investigated. The lowest amounts of Ch or Cat added (1 wt%) produced better interactions among PLA, PHB and plasticizer. Chitosan produced some bead defects in the fibers, which leads to a reduction of the mechanical performance on biocomposites. Catechin antioxidant effect improved the thermal stability of biocomposites and produced beads-free fibers with better mechanical performance. All biocomposites were disintegrated in composting conditions showing their possible applications as biodegradable films. © 2016 Elsevier Ltd. All rights reserved.

Keywords: PLA PHB Chitosan Catechin Plasticizer Electrospinning

1. Introduction The environmental needs on the reduction of petrochemical sources consumption for the production of plastics and the accumulation of high amounts of plastic wastes have led to a growing interest on the use of biobased and biodegradable polymers for several short term applications such as food packaging and agricultural mulch films. Poly(lactic acid) (PLA), synthesized by ring open polymerization of lactic acid that is obtained by fermentation of dextrose, which in turn comes from renewable agricultural sources (i.e.: corn, cellulose and other polysaccharides), is currently the most used biopolymer [1,2]. It is already being commercialized as rigid packaging, containers, cups and cutlery, among others products [1]. However, the use of PLA as flexible film is restricted due to its low deformation at break, thermal stability and crystallization rate and

* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (M.P. Arrieta), [email protected]
pez), [email protected] (D. Lo
pez), [email protected] (J.M. Kenny), lpeponi@ (J. Lo ictp.csic.es (L. Peponi).

degree [1,3e7]. Thus, extensive research efforts have been focused on PLA modification for extending its application as flexible films, such as copolymerization [6,8,9], blending [3,10e12] and the addition of modifiers such as plasticizers [5,7,13] or filler materials to form composites [14e17] and nanocomposites [4,6,18,19]. Poly(hydroxybutyrate) (PHB) is the best known poly(hydroxyalkanoate) (PHA) synthesized by controlled bacterial fermentation with highly ordered stereochemical structure, which results in large crystallinity [3,20]. PHB presents high fragility as well as the difficulties of processing by melt extrusion, due to the narrow processing window, have also led to the search of new blending strategies to extend its industrial applications [20]. Consequently, blending PLA with PHB represents a simple approach to improve both polymer matrices properties by producing synergic effects. In this sense, it has been shown that 25 wt% of PHB produces a nucleating effect on PLA matrix enhancing its crystallinity, barrier properties and hydrophobicity [3,21,22]. Meanwhile, PLA reduces PHB brittleness and, thus, improves its processability [23,24]. However, PLA-PHB blends still remains brittleness and it makes necessary the addition of plasticizers to improve their processability and ductile properties as well as to get the flexibility required for films manufacturing [10]. Citrate-based plasticizers, derived from naturally occurring citric acid, are widely used as

http://dx.doi.org/10.1016/j.polymdegradstab.2016.02.027 0141-3910/© 2016 Elsevier Ltd. All rights reserved.

Please cite this article in press as: M.P. Arrieta, et al., Effect of chitosan and catechin addition on the structural, thermal, mechanical and disintegration properties of plasticized electrospun PLA-PHB biocomposites, Polymer Degradation and Stability (2016), http://dx.doi.org/ 10.1016/j.polymdegradstab.2016.02.027

2

M.P. Arrieta et al. / Polymer Degradation and Stability xxx (2016) 1e12

biopolymer plasticizers [25]. For instance, acetyl(tributyl citrate) (ATBC) has been suggested as one of the most efficient plasticizers for PLA, PHB and PLA-PHB blends [10,24e28]. One cost effective way to optimize PLA and PHB performance for sustainable film applications is the production of composites using different types of natural fillers [15,20]. Natural fillers provide some advantages such as low density, no toxicity and low environmental impact [29]. Polymer based composites offers the opportunity to obtain a material with enhanced elastic modulus and low weight [30]. In this work, two fillers were independently added, chitosan (Ch) and catechin (Cat) to offer some reinforcement to plasticized PLA-PHB matrix. Chitosan, a cationic polysaccharide obtained from chitin crustacean wastes, has gain attention in the industry due to its useful properties for film production including biodegradability, biocompatibility, non-toxicity, low permeability to oxygen and its inherent antimicrobial activity [31e33]. Ch posses a large number of hydroxyl and amino groups, which can act as adsorption sites [34]. Catechin is a flavonoid obtained from several species of the plant kingdom, but especially from the green tea [26,35] and grapes [36,37]. Catechin has gained high interest as natural antioxidants for plastic industry for both to protect polymer matrices during thermal processing and for the development of antioxidant active materials [26,38]. Cat has a high amount of hydroxyl groups and it is widely known that catechol groups are able to interact with carboxylic groups of several polymers, including PLA and PHB, by hydrogen bonding interactions [26,39,40]. Even though catechin is still expensive, several low-cost extraction process of phenolic compounds from different natural byproducts are under investigation [41], particularly those from the wine industry residues because of catechin is the major compound in all winery residues from red and white grapes [36]. Although biopolymers matrices can be considerably improved by means of the above mentioned strategies, there are still difficulties in improving biopolymers films production and performance through cost effective processing approaches for industrial applications. To solve this problem, extensive research and industrial attention has been focus on the use of innovative and scalable to industrial processing technologies for the production of biobased films. In this sense, the electrospinning process has gain considerably attention as sustainable processing technology for film manufacturing since it can produce multifunctional thin materials in the form of non-woven fibers from polymeric solutions subjected to high electric fields and at room temperature [42]. Thus, it is expected that electrospun materials based on biobased and biodegradable polymers may find a wide range of industrial applications because of their improved physical properties and low price [43]. Although, the electrospinning process optimization and scale up are required for the commercial production of electrospun materials, it is relatively simple, extremely flexible and low cost and, thus, it is expected that the transfer of an electrospinning technology from laboratory scale level to industrial production can be easily feasible [24,44]. Electrospun materials possess various structural and functional advantages since the size of the final fibers can be tailored by manipulating different parameters of the electrospinning process (i.e.: electrical potential applied, flow rate of the solution and working distance), the polymeric solution (i.e.: concentration, solvent used, viscosity and conductivity and surface tension) and controlling the ambient conditions (i.e.: temperature, humidity, etc.) [45e49]. Thus, the obtained high-performance electrospun polymeric fibers have diameters ranging from the micro to the nanoscale and possess large surface areas, a small inter-fibrous pore size with high porosity that are easy of functionalization [24,50,51]. Moreover, by changing the composition of the fibers, such as blending with different polymers, several physicochemical properties, i.e.: fiber diameter, density, glass

transition temperature and hydrophilicity can be tailored [50]. In an effort to develop flexible PLA-PHB based electrospun mats, in previous work a plasticizer has been added to such systems and the obtained material resulted far stretchable [24]. Since the fiber functionalities may be dominated by the molecules located at the surface of the fiber [52], in this work two different components with high hydroxyl content (Ch and Cat), able to interact with polymer matrices and to be exposed to the mat surface, were added to electrospun plasticized PLA-PHB mat. Thus, with the main objective to develop multifunctional electrospun biocomposites, PLA was blended with 25 wt% of PHB and further plasticized with 15 wt% of ATBC and, then, the ternary PLA-PHB-ATBC blends were loaded with 1 wt% and 5 wt% of chitosan or catechin. The influence of both Ch and Cat on the plasticized PLA-PHB electrospun fibers morphology, structural, thermal and mechanical properties as well as the surface wettability was investigated. Finally, the disintegration under composting conditions at a laboratory scale level was evaluated to obtain information about their compostability as sustainable end-life option after their useful-life. 2. Experimental 2.1. Materials Poly(lactic acid) (PLA 3051, Mn ¼ 110,000 Da, 3 wt% D-isomer, solubility parameter d ¼ 19.5e20.5 MPa1/2 [1]) was supplied by NatureWorks (USA), Poly(hydroxybutyrate) and (PHB, under the trade name P226, Mw ¼ 426,000 Da, d ¼ 18.5e20.1 MPa1/2 [53]) was supplied by Biomer (Krailling, Germany). The rest of additives: acetyl-tri-n-butyl citrate (ATBC, M ¼ 402 g mol1, 98% purity, d ¼ 20.2 MPa1/2 [10]), Chitosan (Ch, degree of deacetylation > 75%, d ¼ 40e42 MPa1/2 [54]) (Sigma Aldrich) and catechin (Cat, 98% purity, anhydrous grade, d ¼ 11.9 MPa1/2 [55]) were purchased from Sigma-Aldrich (Madrid, Spain). Chloroform (99.6% purity, d ¼ 19.0 MPa1/2 [48]) and dimethylformamide (DMF) (99.5% purity, d ¼ 24.9 MPa1/2 [48]) were supplied by Sigma Aldrich. 2.2. Preparation of plasticized PLA-PHB electrospun mats and their composites PLA pellets were pre-dried at 80  C in a vacuum oven overnight, while PHB pellets, Ch, Cat and ATBC were dried at 40  C for 4 h. Ch powder was grinded to reduce the granules size by means of a cutter grinder [12]. Meanwhile, Cat was directly added as received. The polymeric electrospun solutions were prepared at 8 wt% in a solvent mixture of chloroform: N,N-dimethyl-formamide in 80: 20 proportion (CF80: DMF20) [48] at 80  C and 1000 rpm for 2 h. Each formulation was prepared by blending PLA-PHB in 75:25 proportion and plasticized with 15 wt% of ATBC on the basis of our previous results [24]. For the biocomposites plasticized PLA-PHB blends were further reinforced with 1 wt% and 5 wt% of Ch or Cat. The solutions were sonicated during 10 min to improve the particles dispersion previously to be processed [56]. Electrospun biocomposite mats were processed in a coaxial electrospinner (Y flow 2.2.D-XXX, Nanotechnology Solutions) with a vertical standard configuration equipped with two concentric needles and connected to a high voltage power. Each solution was flowed through the inner needle (1.0 mL h1) while the solvent mixture (CF80: DMF20) was flowed through the outer needle (1.0 mL h1) during 4 h to obtain the biocomposites (thickness of about 25e50 mm). The positive and negative voltages applied were set at ± 10.8 kV. Electrospun biocomposites were randomly collected in a grounded aluminum foil collector situated perpendicular to the charged spinneret at 140 mm. The obtained electrospun biocomposites were then vacuumed for 24 h in a vacuum

Please cite this article in press as: M.P. Arrieta, et al., Effect of chitosan and catechin addition on the structural, thermal, mechanical and disintegration properties of plasticized electrospun PLA-PHB biocomposites, Polymer Degradation and Stability (2016), http://dx.doi.org/ 10.1016/j.polymdegradstab.2016.02.027

M.P. Arrieta et al. / Polymer Degradation and Stability xxx (2016) 1e12

chamber at room temperature to eliminate any potential residual solvents and stored in a desiccator before testing. The biocomposite mat formulations and the proportion of each component as well as their designation are summarized in Table 1. 2.3. Characterization techniques The morphology of the chitosan and catechin powder as well as the surface of the obtained mats was studied by a PHILIPS XL30 Scanning Electron Microscope (SEM). Samples were previously sputtered with a gold/palladium layer. The fiber diameters were statistically calculated from the SEM images by means of Fib_thick software executable under image analysis platform Fiji based on ImageJ. The fibers formation was corroborated by means of M568E Nikon Eclipse optical microscope at 100  magnifications equipped with a Nikon sight camera. Static water contact angle measurements were conducted to evaluate the surface wettability of mats with a standard goniometer (EasyDrop-FM140, KRÜSS GmbH, Hamburg, Germany). Drop Shape Analysis SW21; DSA1 software was used to test the water contact angle (WCA, q ). The contact angle was conducted at room temperature by randomly putting 5 drops of distilled water (z2 mL) with a syringe onto the biocomposite surfaces and, after 20 s, the average values of ten measurements for each drop were used with a maximum standard deviation of ±3% [57]. Attenuated total reflectance - Fourier transform infrared spectroscopy (ATR-FTIR) measurements were conducted by a Spectrum One FTIR spectrometer (Perkin Elmer instruments). Spectra were obtained in the 4000e650 cm1 region at room temperature in transmission mode with a resolution of 4 cm1. Thermogravimetric measurements were performed in a TA-TGA Q500 thermal analyzer under dynamic and isothermic mode, both weighing around 5e10 mg. Dynamic measurements were run from 30 to 700  C at 10  C min1 under nitrogen atmosphere, while isothermal tests were carried out at a 140  C during 50 min under air conditions. The initial degradation temperatures (T5%) were taken at 5% of mass loss and temperatures at the maximum degradation rate (Tmax) were obtained from the first derivative of the TGA curves (DTG). Dynamic DSC experiments were performed in a Mettler Toledo DSC822e instrument under nitrogen atmosphere (50 mL min1). About 4 mg of each mat were sealed in aluminum pans and heated from 50 to 200  C at a heating rate of 10  C min1. The glass transition temperature (Tg) was taken at the midpoint of heat capacity changes. The cold crystallization temperature (Tcc) and the melting temperature (Tm) were determined and the degree of crystallinity (cc) was calculated through Equation (1):

cc ¼ 100% 

  DH m  DH cc 1 c W PLA DH m

(1)

where DHm is the melting enthalpy, DHcc is the cold crystallization enthalpy, and DHcm is the melting heat associated with pure crystalline PLA (93 J g1) and 1/WPLA is the proportion of PLA in the

3

blend [1]. The mechanical properties of biocomposites were evaluated by tensile test measurements. They were conducted at room temperature by an Instron dynamometer (model 3366) equipped with a 100 N load cell, at a crosshead speed of 10 mm min1 and initial length of 30 mm. Dogbone-style mat samples were used and at least five specimens were tested for each formulation. The crystalline profile of the electrospun biocomposites were examined by X-ray diffraction (XRD) equipment (BRUKER D8 Advance). Scanning was performed on square biocomposite mat surfaces (15 mm  15 mm). The diffraction patterns were obtained from a diffractometer using Cu Ka radiation at 40 kV with a scanning step of 0.02 between 5 and 50 with a collection time of 10 s per step. Electrospun biocomposites were disintegrated in composting conditions at laboratory scale level according to the ISO 20200 standard [58]. Electrospun biocomposite samples (15 mm  15 mm) were contained in a textile mesh to allow their easy removal after composting test, but also allowing the access of moisture and microorganisms [59]. They were buried at 4e6 cm depth in perforated plastic boxes containing a solid synthetic wet waste (10% of compost (Mantillo, Spain), 30% rabbit food, 10% starch, 5% sugar, 1% urea, 4% corn oil and 40% sawdust and approximately 50 wt % of water content) and were incubated at aerobic conditions (58  C). Electrospun biocomposites were recovered at 4, 10, 16, 23, 28 and 37 days of the disintegration test. A qualitative check of the physical disintegration in compost as a function of time was done by taken photographs, while the structural and chemical changes were followed by SEM observations and ATR-FTIR measurements, respectively. Significance differences in the wettability, TGA, DSC and mechanical results were statistically calculated by one-way analysis of variance (ANOVA) with OriginPro 8 software using Tukey's test with a 95% confidence level. 3. Results and discussions The microstructure of Ch powder was observed by SEM. Initially chitosan granules were irregular with a size between 80 and 200 mm (Fig. 1-a). Meanwhile, the size of Ch granules was reduced by mechanical grinding to values between 50 and 100 mm (Fig. 1-b). Catechin particles resulted in flakes of about 20e50 mm (Fig. 1-c). The optical observations indicates that appropriate electrospinning processing conditions have been successfully achieved for the preparation of randomly oriented, uniform and almost defectfree plasticized PLA-PHB fibers (Fig. 2-a), as it was reported in a previous work [24]. Fig. 1-d shows, as an example, the visual appearance of PLA-PHB-ATBC mat formulation. The morphological aspects and the average fiber diameter of the obtained mats were also studied by SEM. The PLA-PHB-ATBC mat presents slightly coarse fibers with average fiber diameters of 350 ± 50 nm (Fig. 2a0 ). Chitosan loaded electrospun PLA-PHB-ATBC fibers show some spindle-like defects (beads), mainly when it was added in 5 wt% amount (PLA-PHB-ATBC-Ch5%) (Fig. 2-c and c0 ). A small amount of beads were observed in PLA-PHB-ATBC-Cat1% (Fig. 2-d and d0 ).

Table 1 Electrospun biocomposite mat formulations. Formulations

PLA (wt%)

PHB (wt%)

ATBC (wt%)

Ch (wt%)

Cat (wt%)

PLA-PHB-ATBC PLA-PHB-ATBC-Ch1% PLA-PHB-ATBC-Ch5% PLA-PHB-ATBC-Cat1% PLA-PHB-ATBC-Cat5%

63.75 63 60 63 60

21.25 21 20 21 20

15 15 15 15 15

e 1 5 e e

e e e 1 5

Please cite this article in press as: M.P. Arrieta, et al., Effect of chitosan and catechin addition on the structural, thermal, mechanical and disintegration properties of plasticized electrospun PLA-PHB biocomposites, Polymer Degradation and Stability (2016), http://dx.doi.org/ 10.1016/j.polymdegradstab.2016.02.027

4

M.P. Arrieta et al. / Polymer Degradation and Stability xxx (2016) 1e12

Fig. 1. SEM micrographs of the granulometries of: a) chitosan powder, b) chitosan powder after the mechanical grinding and c) catechin powder. d) Visual appearance of electrospun PLA-PHB-ATBC mat.

Meanwhile, some beads were also observed in the electrospun composite with 5 wt% of Cat (PLA-PHB-ATBC-Cat5%) as reveals Fig. 2-e and e0 . No significant effects were observed on the average fiber diameters with the addition of chitosan, resulting in 250 ± 100 nm for PLA-PHB-ATBC-Ch1% (Fig. 2-b0 ) and 300 ± 100 nm for PLA-PHB-ATBC-Ch5% (Fig. 2-c0 ). The average fiber diameters of chitosan loaded mats also presented scattered values mainly due to the formation of the spindle-like defects such as beads which could influence the formation of fibers with different lengths [52]. Moreover, although the chitosan particles were dispersed in the organic solvent mixture (CF80: DMF20), the beads formations can be also related with the low solubility of chitosan in organic solvents as confirmed by the differences in the solubility parameters. On the other hand, the average fiber diameter was reduced by increasing the amount of catechin. Indeed, the average fiber diameter of PLA-PHB-ATBC was reduced from 350 ± 50 nm to 250 ± 50 nm for PLA-PHB-ATBC-Cat1% (Fig. 2-d0 ) and to 200 ± 50 nm for PLA-PHB-ATBC-Cat5% (Fig. 2-e0 ). This average fiber diameter reduction with catechin addition can be ascribed to the better interaction between both polymer matrices and the plasticizer due to Cat presence by means of hydrogen bonding interactions [26]. Moreover, they could be also reduced as a result of the increased Coulomb forces on the jet due to the high surface charge of Cat which favors the elongation of the polymeric drops resulting in thinner fibers. Similar findings have been previously reported in electrospun PLA-PHB blends reinforced with cellulose nanocrystals which also present high amount of hydroxyl groups and high surface charge [56]. The water contact angle (WCA) of PLA-PHB-ATBC (94.7 ± 2.6 ) (Fig. 2-a00 ) was significantly (p < 0.05) reduced in the biocomposites by increasing the amount of Ch or Cat. Ch and Cat present high amount of OH-groups, which have surface orientation, leading to an increase in the surface hydrophilicity of the biocomposite mats. Higher reductions on the WCA were observed for Ch

biocomposites, PLA-PHB-ATBC-Ch1% ¼ 69.8 ± 0.5 (Fig. 2-b00 ) and PLA-PHB-ATBC-Ch5% ¼ 60.6 ± 2.4 (Fig. 2-c00 ) than for Cat, PLAPHB-ATBC-Cat1% ¼ 88.1 ± 0.9 (Fig. 2-d00 ) and PLA-PHB-ATBCCat5% ¼ 79.4 ± 1.3 (Fig. 2-e00 ), probably due to the greater water affinity of Ch which is highly soluble under wet conditions [11], and also due to the higher amount of beads present in Ch based mats which produces defective fibers with flatter regions that facilitate the penetration of the water droplets into the mat surface increasing its wettability. The FTIR spectra (Fig. 3) showed the main characteristic bands of PLA and PHB as they were well described in a previous work [24]. Meanwhile, some differences were observed for the biocomposites. In catechin incorporated samples two peaks at 1521 cm1 and 1620 cm1 (grey arrows in Fig. 3-a) appeared, which correspond to stretching vibrations of the C]C group of the catechin aromatic ring [60]. A small shoulder is observed at 1600 cm1 in chitosan incorporated samples related with the amide I absorption [31]. The electrospun biocomposites in the region of eOH stretch (3600e3000 cm1) showed a broad peak related with the free hydroxyl groups (Fig. 3-b), which is particularly intense in the case of PLA-PHB-ATBC-Cat5% biocomposite. Similarly, there is a shoulder observed at about 3200 cm1 in catechin loaded samples, attributed to intramolecular and intermolecular self-associated phenolic hydroxyl groups [38], it was more marked in PLA-PHBATBC-Cat5% as a result of the high amount of catechin with exposed eOH surface groups. There is an increase of the band at 2940 cm1 for all composites, particularly in the PLA-PHB-ATBCCat1% (Fig. 3-b), probably due to the catechin eOH bonded with the carbonyl groups of PLA, PHB and ATBC by hydrogen bonding interactions [26]. The effect of Ch and Cat on the thermal properties of the plasticized electrospun PLA-PHB blends was investigated by thermogravimetric dynamic measurements and the main thermal parameters obtained from the TGA (Fig. 4-a) and DTG (Fig. 4-b)

Please cite this article in press as: M.P. Arrieta, et al., Effect of chitosan and catechin addition on the structural, thermal, mechanical and disintegration properties of plasticized electrospun PLA-PHB biocomposites, Polymer Degradation and Stability (2016), http://dx.doi.org/ 10.1016/j.polymdegradstab.2016.02.027

M.P. Arrieta et al. / Polymer Degradation and Stability xxx (2016) 1e12

5

Fig. 2. Electrospun PLA-PHB-ATBC and the biocomposites Optical (left column), SEM observation (middle column) and water contact angles (right column). a) PLA-PHB-ATBC, b) PLA-PHB-ATBC-Ch1%, c) PLA-PHB-ATBC-Ch5%, d) PLA-PHB-ATBC-Cat1% and e) PLA-PHB-ATBC-Cat5%.

curves are summarized in Table 2. Fig. 4 also includes the thermograms of catechin and chitosan powders to better understand the interactions between these components and the polymer matrices. The addition of both, Ch and Cat, decreased the onset

degradation temperature (T5%). The previously reported results of unplasticized PLA-PHB mats have been included in Table 2 for comparison [24]. Plasticized electrospun PLA-PHB mats showed two thermal degradation processes, the first one related to the PHB

Please cite this article in press as: M.P. Arrieta, et al., Effect of chitosan and catechin addition on the structural, thermal, mechanical and disintegration properties of plasticized electrospun PLA-PHB biocomposites, Polymer Degradation and Stability (2016), http://dx.doi.org/ 10.1016/j.polymdegradstab.2016.02.027

6

M.P. Arrieta et al. / Polymer Degradation and Stability xxx (2016) 1e12

Fig. 3. FTIR spectrum of biocomposites in the region of: a) 650e1900 cm1 and b) 2700e3750 cm1.

(TmaxI) degradation and the second (TmaxII) to the PLA decomposition [3]. There is a smaller previous degradation process in the temperature range between 125  C and 200  C related with the loss of ATBC [10]. The addition of Ch in 1 wt % shifted the Tmax values of both, PHB (TmaxI, p < 0.05) and PLA (TmaxII, p > 0.05) to lower values. The main thermal degradation of chitosan occurs in the range of 250e400  C and it is related with the degradation of the saccharide structure, but at lower degradation temperatures (Tmax of chitosan powder around 300  C) degrade the deacetylated molecules [61], that can be influencing the TmaxII. However, by increasing the

amount of chitosan to 5 wt% an increase on the Tmax value of PHB (TmaxI) and PLA (TmaxII) was observed. Catechin addition in 1 wt % slightly increased the TmaxI of PHB (around 3  C), while it considerably increased the TmaxII of PLA of about 15  C (p < 0.05). Although these results showed an effective stabilizing effect for both polymer matrices, they suggest more stabilization efficiency in the case of PLA matrix. Higher amount of catechin (5 wt%) also stabilized PHB by shifting the TmaxI to higher values, but it does not stabilize the PLA matrix showed by a significant (p < 0.05) decrease of TmaxII. This behavior can be due to self-association of catechin

Fig. 4. Biocomposite mats results: a) TGA, b) DTG, c) isothermal TGA and d) DSC.

Please cite this article in press as: M.P. Arrieta, et al., Effect of chitosan and catechin addition on the structural, thermal, mechanical and disintegration properties of plasticized electrospun PLA-PHB biocomposites, Polymer Degradation and Stability (2016), http://dx.doi.org/ 10.1016/j.polymdegradstab.2016.02.027

M.P. Arrieta et al. / Polymer Degradation and Stability xxx (2016) 1e12

7

Table 2 TGA and DSC thermal properties of electrospun biocomposite mats (n ¼ 2). Formulations

TGA parameters T5% ( C)

PLA-PHB PLA-PHB-ATBC PLA-PHB-ATBC-Ch1% PLA-PHB-ATBC-Ch5% PLA-PHB-ATBC-Cat1% PLA-PHB-ATBC-Cat5% a-d

a

208.2 191.4b 184.7c 186.9b,c 185.4c 184.7c

DSC parameters

TmaxI ( C) a

256.7 272.1b 263.2c 273.3b 275.0b 275.2b

TmaxII ( C) a,b,c

334.5 340.8a,b 323.1a,c 348.2a,b,d 355.0d 308.6c

Tg ( C) a

51.0 26.0b,c 25.6b,c 24.8b,c 24.b 27.3c

Tcc ( C) a

107.6 80.7b 63.0c 67.0c 67.0c 66.3c

DHcc (J g1) 15.1 15.1 16.8 21.3 9.1 8.9

TmI ( C) a

154.8 147.5b 146.5b 147.2b 144.0b 144.0b

TmII ( C) a

173.7 162.5b 167.9c 167.3c 164.3c 165.0b,c

DHm (Jg1)

cc (%)

38.1 38.1 31.9 37.2 33.1 33.9

56.6a 38.8b 25.8c 28.5c 40.9b 44.8b

Different superscripts within the same column indicate significant differences between formulations (p < 0.05).

particles, already commented in FTIR results. The non-associated eOH groups were available to protect the polymer thermal degradation at the first stage shifting the TmaxI of the PHB to higher values, and then the degradation at higher temperatures is accelerated [26]. The thermal stability of the mat was also studied by thermogravimetric analysis conducted under isothermal mode during 50 min at 140  C, which is immediately before the onset degradation temperature of plasticized PLA-PHB calculated at 1% of mass loss (T1% ¼ 142  C). It was observed that PLA-PHB-ATBC lost 14% of the initial weight in 50 min. Although, both particles improved the thermal stability of PLA-PHB-ATBC, catechin offered major protection to the polymer from the thermal degradation than chitosan due to their well know antioxidant capacity. The stabilization effect of Cat was more marked for PLA-PHB-ATBC-Cat1% biocomposite (7% of weight loss) than for PLA-PHB-ATBC-Cat5% counterpart (10% of weight loss), in well agreement with dynamic TGA results. These findings suggest that both Cat and Ch are able to improve the thermal stability of PLA-PHB-ATBC that results interesting for several applications that require further processing, for instance for the development of multilayer packaging systems. DSC thermograms for the first heating scan of the electrospun biocomposites are reported in Fig. 4-d while the main thermal properties are summarized in Table 2. The DSC results of PLA-PHB electrospun mat previously reported have been also included for comparison [24]. The Tg values of all mats were considerably (p < 0.05) lower than that of the electrospun PLA-PHB mat previously reported (Tg ¼ 51  C) due to the plasticizer presence. No significant changes on the Tg values were observed due to Ch or Cat addition. PLA-PHB-ATBC mat shows an exothermic peak centered at 80.7  C due to the cold crystallization of PLA. Ch and Cat significantly (p < 0.05) shifted the cold crystallization of electrospun biocomposites to lower temperatures, showing that the recrystallization of PLA is influenced due to the Ch or Cat particles. Two melting peaks were observed in PLA-PHB-ATBC mat due to the melting of PLA (around 145  C) and the melting of PHB at about 163  C with two maximums, one at 160  C that corresponds to the melting of the as-formed PHB crystals during electrospinning process and the other one at 164  C which corresponds to the recrystallized PHB crystals formed during DSC heating [21,26,27]. While no changes or a slightly decrease on the Tm of PLA was observed for biocomposites, they presented an increase (p < 0.05) on the Tm of PHB with only one maximum that can be related with an improvement in the interfacial adhesion among PLA, PHB and ATBC due to Ch or Cat presence. Although no significant changes were observed in the Tm values of PLA due to Ch addition, the area of PLA melting decreased with a consequent reduction on the melting enthalpy (DHm). Chitosan is an amorphous polymer and retards the crystallization rate of PLA forming imperfect crystal structures [62] that present lower onset melting temperature as can be seen in the endothermic DSC curves (Fig. 4 d). Thus, the degree of crystallinity was decreased in chitosan added samples

(p < 0.05). Meanwhile, the electrospun biocomposites with catechin reached the highest crystallinity degree. Cat was able to reduce the melting temperature of PLA (of about 3.5  C) showing that the better dispersed Cat particles lead to an improvement on the interaction between PLA and PHB, which is in good accordance with a previous work on the corresponding melt-extruded samples [26]. Fig. 5 displays the X-ray diffraction pattern of the electrospun PLA-PHB-ATBC, which shows one broad peak centered at 2q ¼ 30 , related with the formation of small PLA crystallite size and semicrystalline character and the increase of polymer chain mobility, which is able to distort the crystal structure observed in electrospun PLA-PHB (75:25) mat previously reported [24]. The crystalline profile of biocomposites showed the characteristic peaks of PLA at 2q ¼ 16.5 attributed to the typical a crystal form of the crystalline phase of PLA in addition to two small peaks at 2q ¼ 13.6 and 2q ¼ 22.4 typically of PHB [63]. Catechin particles, which are smaller than chitosan granules (Fig. 1), offers higher surface area that allowed to develop a huger interfacial area and a higher nucleation effect, which is favored by the plasticizer presence. In fact, plasticizer positively influenced the nucleation and produced a better packaging of segments leading to better interface interaction between PLA and PHB matrices [3,63]. Catechin promoted faster crystallization of plasticized PLA-PHB, most likely due to hydrogenbonding interactions between catechin hydroxyl groups and carbonyl groups of PLA, PHB and ATBC [26]. The higher granules of chitosan with smaller surface area lead to the formation of beads, which leads to defective fibers with lower crystallinity degree (Table 2). The mechanical properties were investigated by tensile test measurements and the results are summarized in Table 3. The addition of plasticizer increased the polymer chain mobility and, thus, increased the elongation at break while reduced the elastic modulus and tensile strength with respect of electrospun PLA-PHB

Fig. 5. X-ray diffraction pattern of electrospun mats.

Please cite this article in press as: M.P. Arrieta, et al., Effect of chitosan and catechin addition on the structural, thermal, mechanical and disintegration properties of plasticized electrospun PLA-PHB biocomposites, Polymer Degradation and Stability (2016), http://dx.doi.org/ 10.1016/j.polymdegradstab.2016.02.027

8

M.P. Arrieta et al. / Polymer Degradation and Stability xxx (2016) 1e12

mats previously reported [24]. The plasticized biocomposites presented significantly (p < 0.05) higher tensile strength values than PLA-PHB-ATBC mat (Table 3) and also than PLA-PHB mat (6.0 ± 1.0 MPa) [24]. Chitosan added samples presented significant higher tensile strength, but lower elastic modulus and elongation a break than PLA-PHB-ATBC. Catechin also significant reduced εB values, but it was able to significant increase both E and TS values. This different behavior on the mechanical properties between Ch and Cat added biocomposites can be related with the fact that chitosan granules whit higher sizes have less surface area to interact with polymer matrices and also the higher amount of beads leads to lower mechanical performance. The lower dispersion of chitosan granules also created discontinuities in the fiber networks and thus preferential breaking zones. Separation into discrete phases due to particle agglomeration, beads formation, etc., normally occurs in composites, which tends to reduce the final properties of the material [64]. Conversely, the more efficient dispersion of smaller catechin particles resulted in an enhancement in the interfacial adhesion and in a better interaction between PLA and PHB, which results in stiffer materials. However, as frequently in composites, at the expense of the reduction of the elasticity [65]. The reinforcing effect of catechin particles has been previously observed in polypropylene [38], PLA and PLA-PHB blends [26]. Electrospun mats were disintegrated under composting conditions at laboratory scale level and their visual appearance during the disintegrability test are shown in Fig. 6. After 10 days of disintegration, all electrospun mats showed clear signs of disintegration such as increased opacity and increased surface roughness. SEM micrographs (Fig. 7) confirm the lost of structural properties of mats showing hydrolyzed fibers as junctions zones on the mat surfaces after 10 testing days. This was particularly evident in biocomposites whit higher amounts of Ch (PLA-PHB-ATBC-Ch5%, Fig. 7-d) or Cat (PLA-PHB-ATBC-Cat5%, Fig. 7-f), where the beads favor the hydrolysis process. Water absorption and diffusion through the polymeric fibers in the initial phase of disintegration in Ch based biocomposites were faster than in Cat based biocomposites, resulting in higher fiber hydrolysis that leads to small molecules (i.e.: monomers and short-chain oligomers) that are available for the microorganisms attack [59]. Additionally, it seems that the disintegration phenomenon was accelerated due to the addition of Ch and Cat (Fig. 6), in well agreement with the higher wettable surfaces presented by the electrospun biocomposites, as measured by WCA (right Fig. 2). Thus, electrospun biocomposites with higher hydrophilic surfaces resulted more susceptible for hydrolysis that starts the disintegration process, which is then followed by the microorganisms enzymatic degradation. Some changes in compost color were observed at 10 days of composting (Fig. 7 a-ii) due to the aerobic fermentation. After 16 days of hydrolysis the electrospun mats resulted totally breakable and they were recovered in small pieces. Finally, PLA-PHB-ATBC and chitosan based biocomposites were totally disintegrated in 28 days. Whereas catechin based electrospun mats

Table 3 Tensile test results of electrospun PLA-PHB biocomposite mat formulations (n ¼ 5). Formulations

E (MPa)

TS (MPa)

εB (%)

PLA-PHB-ATBC PLA-PHB-ATBC-Ch1% PLA-PHB-ATBC-Ch5% PLA-PHB-ATBC-Cat1% PLA-PHB-ATBC-Cat5%

70 ± 10a 60 ± 10a,b 35 ± 5b 150 ± 30c 135 ± 10c

4.5 ± 1.0a 9.6 ± 1.2b 8.6 ± 1.5c 10.8 ± 2.0b,c 11.5 ± 1.5b

105 ± 10a 46 ± 10b 45 ± 14b 42 ± 8b 50 ± 1b

a-c

Different superscripts within the same column indicate significant differences between formulations (p < 0.05).

needed 37 days to reach the disintegration. Catechin delays the second step of the disintegration process, which is the microorganisms enzymatic attack, because it acts as a nucleating agent increasing the crystallinity of the biocomposites that hinder the action of microorganisms. Finally, the compost at the end of the test resulted in dark humus soil (Fig. 7 a-iii) [22]. Fig. 8 shows the FTIR spectra of electrospun PLA-PHB-ATBC mat and the biocomposites before the exposition to the compost medium at 4 and 10 composting days. The intensity of the stretching of the crystalline carbonyl groups, centered at 1722 cm1, increased for all mats with the composting time as a consequence of the hydrolytic degradation, which results in some increase in the number of carboxylic end groups in the polymer chains [16,59]. This band was accompanied with a broad band between 3400 and 3200 cm1 due to the increased OeH stretching of the carboxylic end groups as it is shown as example for PLA-PHB-ATBC in Fig. 8-a. Also an increase of the band at 975 cm1 due to OeH bend was observed. Around 1600 cm1 appears a broad band, corresponding to the formation of carboxylate anions at the chain ends due to the hydrolytic degradation [17,66]. In fact, microorganisms attacked polymer chains and oligomers leaving more carboxylate anions at the chain end [17]. This band appeared at 4 days in PLA-PHB-ATBC (Fig. 8-b) and the biocomposites with higher amount of Ch (Fig. 8d) and Cat (Fig. 8-f). Meanwhile, it appeared after 10 days in composting for PLA-PHB-ATBC-Ch1% (Fig. 8-c) and PLA-PHB-ATBCCat1% (Fig. 8-e). These results confirm that the higher amount of Ch and Cat promotes faster hydrolysis favoring the microorganisms attack. 4. Conclusions Flexible electrospun biocomposites based on plasticized PLAPHB blends added with chitosan or catechin were developed. Morphological investigations of the obtained biocomposites revealed that while 1 wt% of Ch or Cat produced some fiber structural changes (i.e.: smaller diameters and bead-free electrospun fibers), 5 wt% of Ch and Cat produced some structural defects. Cat induced a decrease of the average fiber diameter, but no significant effects were observed on the average fiber diameters of chitosan based biocomposites. In addition, chitosan produced some bead defects, while catechin produced mainly beads-free biocomposites, mostly at low amount (PLA-PHB-ATBC-Cat1%). The wettability of the biocomposites was increased with increasing amount of polar particles. Chitosan based formulations showed more hydrophilic character. Dynamic and isothermal TGA reveals that PLA-PHB-ATBC-Cat1% was the most effective formulation in improving the thermal stability of the electrospun biocomposite mats. DSC showed that Cat improved in turn the ability of the polymer matrix to crystallize, and X-ray diffraction profiles revealed the appearance of the typical crystalline structures of PLA and PHB in biocomposites, amorphous without particles. The addition of Ch and Cat always resulted in biocomposites with increased tensile strength at the expense of the reduction of the elongation at break. Nevertheless, the addition of the smaller Cat particles led to a higher nucleation effect and better interaction between PLA and PHB, which displays biocomposites with increased elastic modulus and tensile strength. All biocomposites were disintegrated in composting conditions as a sustainable endlife option showing their possible applications as biodegradable films. In summary, this study showed that the electrospun plasticized PLA-PHB biocomposites loaded with both chitosan and catechin are promising materials for biodegradable film applications in several fields, such as agricultural mulch films or films for food packaging. In view of the well-known antimicrobial activity of chitosan as well

Please cite this article in press as: M.P. Arrieta, et al., Effect of chitosan and catechin addition on the structural, thermal, mechanical and disintegration properties of plasticized electrospun PLA-PHB biocomposites, Polymer Degradation and Stability (2016), http://dx.doi.org/ 10.1016/j.polymdegradstab.2016.02.027

M.P. Arrieta et al. / Polymer Degradation and Stability xxx (2016) 1e12

9

Fig. 6. Visual appearance of electrospun biocomposites before and after different incubation days under composting conditions.

Fig. 7. a) Visual appearance of compost i) before, ii) after 10 days and at iii) 37 days of disintegration. SEM observations of biocomposites: b) PLA-PHB-ATBC, c) PLA-PHB-ATBC-Ch1%, d) PLA-PHB-ATBC-Ch5%, e) PLA-PHB-ATBC-Cat1% and f) PLA-PHB-ATBC-Cat5% different degradation time under composting conditions.

Please cite this article in press as: M.P. Arrieta, et al., Effect of chitosan and catechin addition on the structural, thermal, mechanical and disintegration properties of plasticized electrospun PLA-PHB biocomposites, Polymer Degradation and Stability (2016), http://dx.doi.org/ 10.1016/j.polymdegradstab.2016.02.027

10

M.P. Arrieta et al. / Polymer Degradation and Stability xxx (2016) 1e12

Fig. 8. FTIR at different disintegration times under composting conditions: a) Infrared spectra (3800e2700 cm1) of PLA-PHB-ATBC. Infrared spectra (1850e650 cm1) of: b) PLAPHB-ATBC, c) PLA-PHB-ATBC-Ch1%, d) PLA-PHB-ATBC-Ch5%, e) PLA-PHB-ATBC-Cat1% and f) PLA-PHB-ATBC-Cat5%.

as the well-known antioxidant activity of catechin, further assessment will be needed in order to evaluate the feasibility of these biocomposites as active film materials. Acknowledgements Authors thank Spanish Ministry of Science and Innovation (MAT2013-48059-C2-1-R and MAT2014-55778-REDT) and Regional Government of Madrid (S2013/MIT-2862). M. P. Arrieta and L. Peponi are recipients of a “Juan de la Cierva” contract (FJCI2014-20630) and “Ramon y Cajal” contract (RYC-2014-15595) from the Spanish Ministry of Economy and Competitiveness, respectively. References [1] R. Auras, B. Harte, S. Selke, An overview of polylactides as packaging materials, Macromol. Biosci. 4 (2004) 835e864.

[2] M. Jamshidian, E.A. Tehrany, M. Imran, M. Jacquot, S. Desobry, Poly-lactic acid: production, applications, nanocomposites, and release studies, Compr. Rev. Food Sci. Food Sci. F. 9 (2010) 552e571.
pez, A. Herna
ndez, E. Rayo
n, Ternary PLA-PHB-Limonene [3] M.P. Arrieta, J. Lo blends intended for biodegradable food packaging applications, Eur. Polym. J. 50 (2014) 255e270.
nez, R.A. Ruseckaite, L. Ave
rous, Structure and properties [4] V.P. Martino, A. Jime of clay nano-biocomposites based on poly(lactic acid) plasticized with polyadipates, Polym. Adv. Technol. 22 (2011) 2206e2213.
nez, Synthesis and characterization of [5] N. Burgos, D. Tolaguera, S. Fiori, A. Jime lactic acid oligomers: evaluation of performance as poly(lactic acid) plasticizers, J. Polym. Environ. 22 (2014) 227e235. [6] G.L. Re, S. Benali, Y. Habibi, J.-M. Raquez, P. Dubois, Stereocomplexed PLA nanocomposites: from in situ polymerization to materials properties, Eur. Polym. J. 54 (2014) 138e150. [7] A. Ruellan, A. Guinault, C. Sollogoub, V. Ducruet, S. Domenek, Solubility factors as screening tools of biodegradable toughening agents of polylactide, J. Appl. Polym. Sci. 132 (2015).
ndez, A. Fern
[8] I. Navarro-Baena, A. Marcos-Ferna andez-Torres, J.M. Kenny, L. Peponi, Synthesis of PLLA-b-PCL-b-PLLA linear tri-block copolymers and their corresponding poly(ester-urethane)s: effect of the molecular weight on their crystallisation and mechanical properties, RSC Adv. 4 (2014) 8510e8524.
ez, J.M. Kenny, A. Marcos-Fern
[9] L. Peponi, I. Navarro-Baena, J.E. Ba andez, Effect

Please cite this article in press as: M.P. Arrieta, et al., Effect of chitosan and catechin addition on the structural, thermal, mechanical and disintegration properties of plasticized electrospun PLA-PHB biocomposites, Polymer Degradation and Stability (2016), http://dx.doi.org/ 10.1016/j.polymdegradstab.2016.02.027

M.P. Arrieta et al. / Polymer Degradation and Stability xxx (2016) 1e12

[10]

[11]

[12]

[13]

[14]

[15]

[16]

[17]

[18]

[19]

[20]

[21]

[22]

[23]

[24]

[25]

[26]

[27]

[28]

[29]

[30]

[31]

[32]

[33]

[34]

[35]

of the molecular weight on the crystallinity of PCL-b-PLLA di-block copolymers, Polymer 53 (2012) 4561e4568.
pez, A. Jime
nez, Combined effect of poly(M.P. Arrieta, M.D. Samper, J. Lo hydroxybutyrate) and plasticizers on polylactic acid properties for film intended for food packaging, J. Polym. Environ. 22 (2014) 460e470. H. Gartner, Y. Li, E. Almenar, Improved wettability and adhesion of polylactic acid/chitosan coating for bio-based multilayer film development, Appl. Surf. Sci. 332 (2015) 488e493. J. Bonilla, E. Fortunati, M. Vargas, A. Chiralt, J.M. Kenny, Effects of chitosan on the physicochemical and antimicrobial properties of PLA films, J. Food Eng. 119 (2013) 236e243.
pez, S. Ferra
ndiz, M.A. Peltzer, Characterization of PLAM.P. Arrieta, J. Lo limonene blends for food packaging applications, Polym. Test. 32 (2013) 760e768. A. Carbonell, T. Boronat, E. Fages, S. Girones, E. Sanchez-Zapata, J.A. PerezAlvarez, et al., Wet-laid technique with Cyperus esculentus: development, manufacturing and characterization of a new composite, Mater Des. 86 (2015) 887e893. M.A.S. Anwer, H.E. Naguib, A. Celzard, V. Fierro, Comparison of the thermal, dynamic mechanical and morphological properties of PLA-Lignin & PLATannin particulate green composites, Compos Part B Eng 82 (2015) 92e99. E. Fortunati, D. Puglia, M. Monti, C. Santulli, M. Maniruzzaman, M.L. Foresti, et al., Okra (Abelmoschus esculentus) fibre based pla composites: mechanical behaviour and biodegradation, J. Polym. Environ. 21 (2013) 726e737. E. Fortunati, I. Armentano, A. Iannoni, M. Barbale, S. Zaccheo, M. Scavone, et al., New multifunctional poly(lactide acid) composites: mechanical, antibacterial, and degradation properties, J. Appl. Polym. Sci. 124 (2012) 87e98.
n, J. Lo
pez, J.M. Kenny, MultiM.P. Arrieta, E. Fortunati, F. Dominici, E. Rayo functional PLA-PHB/cellulose nanocrystal films: processing, structural and thermal properties, Carbohydr. Polym. 107 (2014) 16e24. F. Luzi, E. Fortunati, D. Puglia, R. Petrucci, J.M. Kenny, L. Torre, Study of disintegrability in compost and enzymatic degradation of PLA and PLA nanocomposites reinforced with cellulose nanocrystals extracted from Posidonia Oceanica, Polym. Degrad. Stabil. 121 (2015) 105e115. L.D. Alberti, O.F. Souza, D.Z. Bucci, I.O. Barcellos, Study on physical and mechanical properties of PHB biocomposites with rice hull ash, Mater Sci. Forum 775e776 (2014) 557e561. M. Zhang, N.L. Thomas, Blending polylactic acid with polyhydroxybutyrate: the effect on thermal, mechanical, and biodegradation properties, Adv. Polym. Tech. 30 (2011) 67e79.
n, J. Lo
pez, J.M. Kenny, PLA-PHB/ M.P. Arrieta, E. Fortunati, F. Dominici, E. Rayo cellulose based films: mechanical, barrier and disintegration properties, Polym. Degrad. Stabil. 107 (2014) 139e149. C. Vogel, H.W. Siesler, Thermal degradation of poly(ε-caprolactone), poly(Llactic acid) and their blends with poly(3-hydroxy-butyrate) studied by TGA/ FT-IR spectroscopy, Macromol. Symp. 265 (2008) 183e194.
pez, D. Lo
pez, J.M. Kenny, L. Peponi, Development of plastiM.P. Arrieta, J. Lo cized electrospun PLA-PHB based materials for food packaging: structural, thermal, mechanical and disintegration properties, Eur. Polym. J. 73 (2015) 433e446.
rous, V. Ducruet, Analysis of the C. Courgneau, S. Domenek, A. Guinault, L. Ave structure-properties relationships of different multiphase systems based on plasticized poly(lactic acid), J. Polym. Environ. 19 (2011) 362e371.
pez, E. Rayo
n, L.F. Barral-Losada, J.M. Lo
pezM.P. Arrieta, M.D.M. Castro-Lo ~ o, J. Lo
pez, et al., Plasticized poly(lactic acid)-poly(hydroxybutyrate) Vilarin (PLA-PHB) blends incorporated with catechin intended for active foodpackaging applications, J. Agr. Food Chem. 62 (2014) 10170e10180.
pez, J.M. Kenny, Bionanocomposite M.P. Arrieta, E. Fortunati, F. Dominici, J. Lo films based on plasticized PLA-PHB/cellulose nanocrystal blends, Carbohydr. Polym. 121 (2015) 265e275. M. Erceg, T. Kova ci
c, I. Klari
c, Thermal degradation of poly(3-hydroxybutyrate) plasticized with acetyl tributyl citrate, Polym. Degrad. Stabil. 90 (2005) 313e318. D. García-García, A. Carbonell, M.D. Samper, D. García-Sanoguera, R. Balart, Green composites based on polypropylene matrix and hydrophobized spend coffee ground (SCG) powder, Compos Part B Eng 78 (2015) 256e265. n, Statistical analysis of the L. Peponi, J. Biagiotti, J.M. Kenny, I. Mondrago mechanical properties of natural fibers and their composite materials. II. Composite materials, Polym. Compos. 29 (2008) 321e325.
s, A. Chiralt, J.M. Kenny, Physical, structural and J. Bonilla, E. Fortunati, L. Atare antimicrobial properties of poly vinyl alcoholechitosan biodegradable films, Food Hydrocoll. 35 (2014) 463e470.
ndez-Pan, J.I. Mate
, C. Gardrat, V. Coma, Effect of chitosan molecular I. Ferna weight on the antimicrobial activity and release rate of carvacrol-enriched films, Food Hydrocoll. 51 (2015) 60e68.
pez-Caballero, M.C. Go
mez-Guille
n, M. Ferna
ndezM.Y. Arancibia, M.E. Lo
ndez-Martín, P. Montero, Antimicrobial and rheological García, F. Ferna properties of chitosan as affected by extracting conditions and humidity exposure, LWT - Food Sci. Tech. 60 (2015) 802e810. G.Z. Kyzas, N.A. Travlou, E.A. Deliyanni, The role of chitosan as nanofiller of graphite oxide for the removal of toxic mercury ions, Colloid Surf. B 113 (2014) 467e476.
pez, C.L. De Dicastillo, J.M.L. Vilarin ~ o, M.V.G. Rodríguez, M.D.M. Castro Lo Improving the capacity of polypropylene to be used in antioxidant active films: incorporation of plasticizer and natural antioxidants, J. Agr. Food Chem.

11

61 (2013) 8462e8470. [36] A. Teixeira, N. Baenas, R. Dominguez-Perles, A. Barros, E. Rosa, D.A. Moreno, et al., Natural bioactive compounds from winery by-products as health promoters: A review, Int. J. Mol. Sci. 15 (2014) 15638e15678. [37] T.M. Rababah, N.S. Hettiarachchy, R. Horax, Total phenolics and antioxidant activities of fenugreek, green tea, black tea, grape seed, ginger, rosemary, gotu kola, and ginkgo extracts, vitamin E, and tert-butylhydroquinone, J. Agr. Food Chem. 52 (2004) 5183e5186.
pez de Dicastillo, M.D.M. Castro-Lo
pez, J.M. Lo
pez-Vilarin ~ o, [38] C. Lo
lez-Rodríguez, Immobilization of green tea extract on polyM.V. Gonza propylene films to control the antioxidant activity in food packaging, Food Res. Int. 53 (2013) 522e528.
pez De Dicastillo, M.D.M. Castro-Lo
pez, A. Lasagabaster, J.M. Lo
pez[39] C. Lo ~ o, M.V. Gonz
Vilarin alez-Rodríguez, Interaction and release of catechin from anhydride maleic-grafted polypropylene films, ACS Appl. Mater Inter 5 (2013) 3281e3289.
~ oz-Bonilla, M. Ferna
ndez-García, Cat[40] M. Alvarez-Paino, G. Marcelo, A. Mun echolic chemistry to obtain recyclable and reusable hybrid polymeric particles as catalytic systems, Macromolecules 46 (2013) 2951e2962. [41] H.N. Rajha, N. Darra, E. Vorobiev, N. Louka, R. Maroun, An environment friendly, low-cost extraction process of phenolic compounds from grape byproducts. optimization by multi-response surface methodology, Food Nut. Sci. 4 (2013) 650e659. [42] M.J. Fabra, A. Lopez-Rubio, J.M. Lagaron, Nanostructured interlayers of zein to improve the barrier properties of high barrier polyhydroxyalkanoates and other polyesters, J. Food Eng. 127 (2014) 1e9. [43] E. Korina, O. Stoilova, N. Manolova, I. Rashkov, Poly(3-hydroxybutyrate)-based hybrid materials with photocatalytic and magnetic properties prepared by electrospinning and electrospraying, J. Mater Sci. 49 (2014) 2144e2153. [44] F.R. Lamastra, D. Puglia, M. Monti, A. Vella, L. Peponi, J.M. Kenny, et al., Poly(εcaprolactone) reinforced with fibres of Poly(methyl methacrylate) loaded with multiwall carbon nanotubes or graphene nanoplatelets, Chem. Eng. J. 195e196 (2012) 140e148. [45] J. Anu Bhushani, C. Anandharamakrishnan, Electrospinning and electrospraying techniques: potential food based applications, Trends Food Sci. Tech. 38 (2014) 21e33. [46] C. Wang, K.W. Yan, Y.D. Lin, P.C.H. Hsieh, Biodegradable core/shell fibers by coaxial electrospinning: processing, fiber characterization, and its application in sustained drug release, Macromol 43 (2010) 6389e6397. [47] J.M. Deitzel, J. Kleinmeyer, D. Harris, N.C. Beck Tan, The effect of processing variables on the morphology of electrospun nanofibers and textiles, Polymer 42 (2001) 261e272. [48] A. Mujica-Garcia, I. Navarro-Baena, J.M. Kenny, L. Peponi, Influence of the processing parameters on the electrospinning of biopolymeric fibers, J. Renew. Mater. 2 (2014) 23e34.
nez, Electrospinning of [49] A. Sonseca, L. Peponi, O. Sahuquillo, J.M. Kenny, E. Gime biodegradable polylactide/hydroxyapatite nanofibers: study on the morphology, crystallinity structure and thermal stability, Polym. Degrad. Stab. 97 (2012) 2052e2059. [50] R. Dai, L.-T. Lim, Release of allyl isothiocyanate from mustard seed meal powder entrapped in electrospun PLAePEO nonwovens, Food Res. Int. 77 (2015) 467e475. [51] L. Peponi, A. Mujica García, J.M. Kenny, Electrospinning of PLA. Poly(lactic acid) science and technology: processing, properties, additives and applications, R. Soc. Chem. (2014) 171e194. [52] C. Kriegel, A. Arrechi, K. Kit, D.J. McClements, J. Weiss, Fabrication, functionalization, and application of electrospun biopolymer nanofibers, Crit. Rev. Food Sci. 48 (2008) 775e797. [53] P.S. Calv~ ao, J.M. Chenal, C. Gauthier, N.R. Demarquette, A. Bogner, J.Y. Cavaille, Understanding the mechanical and biodegradation behaviour of poly(hydroxybutyrate)/rubber blends in relation to their morphology, Polym. Int. 61 (2012) 434e441. [54] R. Ravindra, K.R. Krovvidi, A.A. Khan, Solubility parameter of chitin and chitosan, Carbohydr. Polym. 36 (1998) 121e127. [55] J.H. Kang, S.T. Chung, K.H. Row, Comparison of experimental and calculated solubilities of (þ)-catechin in green tea, J. Ind. Eng. Chem. 8 (2002) 354e358.
pez, D. Lo
pez, J.M. Kenny, L. Peponi, Biodegradable electro[56] M.P. Arrieta, J. Lo spun bionanocomposite fibers based on plasticized PLAePHB blends reinforced with cellulose nanocrystals, Ind. Crop Prod. (2016), http://dx.doi.org/ 10.1016/j.indcrop.2015.12.058.
nchez-N
[57] V. Fombuena, D. García-Sanoguera, L. Sa acher, R. Balart, T. Boronat, Optimization of atmospheric plasma treatment of LDPE films: influence on adhesive properties and ageing behavior, J. Adhes. Sci. Technol. 28 (2014) 97e113. [58] UNE. UNE-EN ISO-20200, Determination of the Degree of Disintegration of Plastic Materials Under Simulated Composting Conditions in a Laboratoryscale Test, 2006.
pez, E. Rayo
n, A. Jime
nez, Disintegrability under composting [59] M.P. Arrieta, J. Lo conditions of plasticized PLAePHB blends, Polym. Degrad. Stabil. 108 (2014) 307e318.
n, A. Ontiveros-Ortega, M. Espinosa-Jimenez, [60] M.M. Ramos-Tejada, J.D.G. Dura R. Perea-Carpio, E. Chibowski, Investigation of alumina/(þ)-catechin system properties. Part I: a study of the system by FTIR-UVeVis spectroscopy, Colloid Surf. B 24 (2002) 297e308. [61] A.T. Paulino, J.I. Simionato, J.C. Garcia, J. Nozaki, Characterization of chitosan

Please cite this article in press as: M.P. Arrieta, et al., Effect of chitosan and catechin addition on the structural, thermal, mechanical and disintegration properties of plasticized electrospun PLA-PHB biocomposites, Polymer Degradation and Stability (2016), http://dx.doi.org/ 10.1016/j.polymdegradstab.2016.02.027

12

M.P. Arrieta et al. / Polymer Degradation and Stability xxx (2016) 1e12

and chitin produced from silkworm crysalides, Carbohydr. Polym. 64 (2006) 98e103. [62] H.T. Au, L.N. Pham, T.H.T. Vu, J.S. Park, Fabrication of an antibacterial nonwoven mat of a poly(lactic acid)/chitosan blend by electrospinning, Macromol. Res. 20 (2012) 51e58. [63] M.A. Abdelwahab, A. Flynn, B.S. Chiou, S. Imam, W. Orts, E. Chiellini, Thermal, mechanical and morphological characterization of plasticized PLA-PHB blends, Polym. Degrad. Stabil. 97 (2012) 1822e1828. [64] L. Peponi, D. Puglia, L. Torre, L. Valentini, J.M. Kenny, Processing of nanostructured polymers and advanced polymeric based nanocomposites, Mater

Sci. Eng. R Rep 85 (2014) 1e46.
Sonseca, S. Camarero-Espinosa, L. Peponi, C. Weder, E.J. Foster, J.M. Kenny, [65] A. et al., Mechanical and shape-memory properties of poly(mannitol sebacate)/ cellulose nanocrystal nanocomposites, J. Polym. Sci. Part A Polym. Chem. 52 (2014) 3123e3133.
pez, E. Gime
nez, et al., [66] I. Navarro-Baena, M.P. Arrieta, A. Sonseca, L. Torre, D. Lo Biodegradable nanocomposites based on poly(ester-urethane) and nanosized hydroxyapatite: plastificant and reinforcement effects, Polym. Degrad. Stabil. 121 (2015) 171e179.

Please cite this article in press as: M.P. Arrieta, et al., Effect of chitosan and catechin addition on the structural, thermal, mechanical and disintegration properties of plasticized electrospun PLA-PHB biocomposites, Polymer Degradation and Stability (2016), http://dx.doi.org/ 10.1016/j.polymdegradstab.2016.02.027