Polyethylene glycol functionalized graphene oxide and its influences on properties of Poly(lactic acid) biohybrid materials

Composites Part B 161 (2019) 651–658

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Polyethylene glycol functionalized graphene oxide and its influences on properties of Poly(lactic acid) biohybrid materials

T

Nguyen Dang Maoa,b,c,1, Hun Jeongd,1, Thi Kim Ngan Nguyena, Thi Mai Loan Nguyene, Thi Vi Vi Doa, Chi Nhan Ha Thuca, Patrick Perréb,c, Sang Cheol Kod, Hong Gun Kimd, Duy Thanh Trana,f,g,∗ a

Faculty of Material Science, University of Science, Vietnam National University Ho Chi Minh city (VNU), Viet Nam LGPM, CentraleSupélec, Université Paris-Saclay, 8-10 rue Joliot-Curie, 91 190, Gif-sur-Yvette, France c LGPM, CentraleSupélec, Université Paris-Saclay, Centre Européen de Biotechnologie et de Bioéconomie (CEBB), 3 rue des Rouges Terres, 51 110, Pomacle, France d Institute of Carbon Technology, Jeonju University, Jeonju, Jeonbuk, 55069, Republic of Korea e CESP/UMR-S 1178, Univ. Paris-Sud, Fac. Pharmacie, INSERM, Université Paris-Saclay, Chatenay Malabry, 92290, France f Center of Excellence for Functional Polymers and NanoEngineering, Nguyen Tat Thanh University, Ho Chi Minh City, Viet Nam g Advanced Materials Institute of BIN Convergence Technology (BK21 plus Global), Dept. of BIN Convergence Technology, Chonbuk National University, Jeonju, Jeonbuk, 54896, Republic of Korea b

A R T I C LE I N FO

A B S T R A C T

Keywords: Poly (lactic acid) Modified graphene oxide Polyethylene glycol Biohybrid materials

A biohybrid material based on poly(lactic acid)(PLA) incorporated with low contents of polyethylene glycol (PEG) functionalized graphene oxide (GO) was prepared via melting process and their structure, morphology, mechanical performance, and thermal properties were studied in detail. SEM and TEM characterizations confirmed that the functionalization of GO with PEG (PEGmGO) promoted its exfoliation into thin exfoliated nanosheets, thereby improving the interactions between PEGmGO filler and PLA matrix at interface. FT-IR spectra showed the presence of strong polar and hydrogen bonding interactions between components in the biohybrid. Mechanical and thermal tests indicated that there was the significant improvement of the stiffness, strength, and thermal stability of such biohybrid material with the addition of 0.3 phr PEGmGO, as compared to pure PLA, PEG-plasticized PLA, PEG-plasticized PLA/GO, and other surveyed PEG-plasticized PLA/PEGmGO biohybrids. This behavior was attributed to the homogeneous dispersion of the PEGmGO nanofillers within PLA matrix along with their strong interfacial interaction. The as-obtained biohybrids show highly potential to be useful in the bioengineering applications.

1. Introduction In recent, the development of novel polymer based-biomaterials has been strongly considered to manage the environmental pollution, which is caused by large amount of the post-consumer polymer waste eliminated each year. Many efforts, including recycling of the postconsumer plastics [1–3] and preparation of the partially or fully biodegradable materials [4–6] have been widely reported. Regarding to the synthesis of partially biodegradable materials, these can be achieved by blending traditional polymer matrix with a suitable amount of biodegradable fillers, such as starch, chitosan, and cellulose fibers, thereby effectively reducing the volume of polymer matrix and also accelerating the biodegradation of polymer [7–11]. However, the

nano/micro-polymer particles, which are formed during degradation of polymer matrix, are found to easily diffuse into underground water sources and cause major problems towards the aquatic ecosystems [12–15]. Therefore, the development of full biodegradable materials has been greatly attracted as the next generation of polymer-based bioproducts in various industrial applications. In this context, poly (lactic acid) (PLA), a famous biodegradable thermoplastic polyester, has been extensively applied in diverse fields, such as bio-packaging and biomedical purposes [16–19]. PLA possesses good stiffness, strength, and thermal plasticity; however, the high cost, brittleness, inappropriate crystallization, low thermal resistance, rapid hydrolysis rate, poor barrier properties, and difficult processability of such polymer are still remaining issues, significantly limiting its practical

∗

Corresponding author. Faculty of Material Science, University of Science, Vietnam National University Ho Chi Minh city (VNU), Viet Nam. E-mail address: [email protected] (D.T. Tran). 1 First authors: Nguyen Dang Mao and Hun Jeong are co-first authors, having equal contribution. https://doi.org/10.1016/j.compositesb.2018.12.152 Received 12 July 2018; Received in revised form 22 December 2018; Accepted 31 December 2018 Available online 02 January 2019 1359-8368/ © 2019 Elsevier Ltd. All rights reserved.

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(HCl, 37%) were provided by Samchun Pure Chemical Co. (Korea). Poly (lactic acid) 4043D with density of 1.24 g/cm3, melt flow index of 0.6 g/min, and melting point of 145–160 °C, was supplied by Prospector® search engine Co. (USA).

applications [20,21]. In order to overcome these complications, considerable efforts have been conducted to satisfy the PLA properties via several approaches, such as modifying, blending, copolymerizing, and physical treatments [22]. Nowadays, nanomaterial science is an evolutionary approach for preparing new material with high performances, reduced prices, but high efficiency [23–25]. The hybridization of ultrafine inorganic nanomaterials at low content with PLA polymer to produce biohybrid materials has demonstrated to be a highly potential trend because the homogeneous dispersion of nanofillers in polymer matrix can result in superior properties to those of conventional composites due to the maximized interfacial adhesion [26]. Recently, biohybrids based on PLA matrix with layered silicates, carbon nanotubes, aluminum hydroxide, layered titanate, andhydroxyapatite have been extensively studied [27,28]. In particular, graphene, graphene oxide (GO) and functionalized GO nanosheets have been impressively concerned as great promising nanofillers, due to large surface area, excellent mechanical properties, high stability, good electrical conductivity, and ease of functionalization [29,30]. Recent reports indicated the mechanical performance, thermal properties, gas barrier, and water vapor permeability of the resulting biohybrid materials were highly improved after addition of graphene-based material [31,32], GO [33], GO modified with silane [34], GO modified with octadecylamine [35], GO modified with stearic acid [36], and GO modified with poly(ethylene glycol) (PEG) into PLA matrix by melting or solution methods. In this regard, the suitable functionalization of GO surface becomes a critical factor to achieve the compatible interfaces to promote the good dispersions of nanofiller into PLA matrix for resulting in enhanced properties of final products. Because GO material contains abundant hydrophilic groups, including hydroxyl, carboxyl, and epoxy groups, it is easy to be grafted with some macromolecules onto its surface through covalent or noncovalent functionalizations. Interestingly, the functionalization of GO with a biocompatible polymer can critically reduce cytotoxic feature of GO to cells and animals in biomedical applications. Poly(ethylene glycol) (PEG) is a very valuable ingredient in biology due to its nontoxicity, biocompatibility, and good solubility in water and various common solvents. The coupling of PEG with other polymers or nanomaterials can efficiently enhance their biocompatibility. In previous reports, researchers successfully applied PEG as an effective plasticizer for PLA matrix to significantly lower the melting temperature, reduce the brittleness, and improve the toughness [37–39]. This also allowed the improvement of processing efficiency for PLA, thereby enhancing thermal stability, mechanical properties, and permeability for diverse applications. In addition, the surface modification of GO nanosheets with PEG (PEGmGO) has been extensively studied in drug delivery application [40,41]. The ultrahigh surface area of PEGmGO has been also appropriate for filling into some polymer matrices to upgrade their properties [42–44]. To the best our knowledge, a biohybrid material based on the PEGmGO nanofillers reinforced PEG plasticizer/PLA(PLAPEG/PEGmGO) have been not studied so far. Therefore, in this study, we prepared PEGmGO through a solution method. Subsequently, we synthesized PLAPEG/PEGmGO biohybrids by a melting processing and investigated the influence of PEGmGO on the mechanical and thermal properties of the resulting biohybrid materials. The obtained results indicated PEGmGO nanosheets can effectively intercalate into the PLA matrix, then producing the significant increase in the properties of the final biohybrid materials.

2.2. Preparation of GO material GO was synthesized from graphite flake by a modified Hummer's method reported elsewhere [45]. In a particular procedure, 100 mL of the concentrated H2SO4 solution was slowly added into a three-neck flask containing 3 g of graphite flakes and 5 g of NaNO3. The suspension was adjusted temperature at about 0 °C and magnetic stirred with 300 rpm. Then, 14 g of KMnO4 was slowly added into suspension. After that, the temperature was increased to 35 °C to allow the oxidation reaction happening for 30 min. During the reaction, the suspension would convert to brown-gray solidify and release of gas. After reaction finished, 300 mL of H2O was added into suspension and the temperature of system was increased and kept at 98 °C for 40 min and then at 68 °C for 20 min. Subsequently, 500 mL of H2O2 solution was added to suspension to reduce generated MnO2 and MnO4−. After 15 min, the suspension was centrifuged with 2000 rpm and washed many times with distilled water to obtain pH of 7. The GO suspension was freezedried to achieve finally powder with constant weight for further experiments. 2.3. Preparation of PEGmGO material To prepare the PEGmGO material, 100 mL of aqueous GO solution (1.0 mg/mL) was added into 100 mL aqueous solution containing 0.5 g of PEG. Subsequently, the obtained solution was mechanically stirred at 60 °C for 24 h. Finally, the PEGmGO was collected by centrifugation, followed by washing several times with DI water and drying in vacuum at 65 °C before it can be used for next steps. 2.4. Preparation of PLAPEG/PEGmGO biohybrid materials To prepare PLAPEG/PEGmGO biohybrid materials, 85 g of PLA matrix, 15 g of PEG as plasticizer, and different amounts of the PEGmGO nanofiller (0.3, 0.6, 0.9, and 1.2 phr) were simultaneously mixed in a Poly Haake mixer with screw rotation rate of 50 rpm at 170 °C for 7 min. Then, the melted compound was cut into small pieces and injected into dumb-bell shaped specimens by a Haake MiniJet injection molding machine at 185 °C and 350 bars for 4 min. For comparison, a biohybrid of PLAPEG/GO was also fabricated through the same process. All biohybrid samples were stored at 23 °C overnight before any further characterizations. Scheme 1 illustrated the procedure for fabrication of the PLAPEG/PEGmGO biohybrid materials. 2.5. Material characterizations Chemical properties of materials were characterized by a Fourier transform infrared (FT-IR) spectrometer Equinox 55 (Burker Co., Germany) in range from 4000 to 400 cm−1 with resolution at 4 cm−1. Crystallinity of GO and hybrid materials was recognized by X-ray diffraction D8 Advance diffractometer (Burker Co., Germany) with 2θ from 3° to 20° and scan rate of 0.03°/s. Morphology and structure of biohybrid materials were investigated by field emission scanning electron microscopy (FE-SEM) Hitachi S-4800 (Hitachi Co., Japan) and transmission electron microscopy (TEM) JEM-1400 Philips (JEOL Co., Japan). The tensile tests were carried out on AG-X Plus 20 kN (Shimadzu Co., Japan) with rate at 50 mm/min. Thermal properties of materials were evaluated in the range from −20 to 250 °C using differential scanning calorimetry (DSC) equipment (Mettle Toledo Co., USA) under N2 environment with heating rate of 10 °C/min. Thermogravimetric analysis (TGA) on the Universal V4.5A (TA Instruments Co. USA) was applied from 0 to 800 °C under N2

2. Experimental 2.1. Materials Graphite flakes and polyethylene glycol (PEG, Mw = 4000 g mol−1) were purchased from Sigma Aldrich Co. (USA). Sulfuric acid (H2SO4, 95–97%), hydrogen peroxide (H2O2, 30%), sodium nitrate (NaNO3), potassium permanganate (KMnO4), acetone (95%), and chloride acid 652

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Scheme 1. Schematic illustration for synthesis of the PLAPEG/PEGmGO biohybrid material.

typical peaks, corresponding to OeH stretching from eOH (3390 cm−1) and eCOOH (3147 cm−1), CeH stretching (2927 cm−1 and 2854 cm−1), C]O stretching from eC]O and eCOOH (1724 cm−1), C]C stretching (1616 cm−1), CeO stretching (1400 cm−1), and CeOeC stretching (1076 cm−1) [46]. Meanwhile, the spectrum of PEGmGO presents some additional characteristics compared to GO, due to the intercalation of PEG chains into GO structure. In this regard, the CeH stretching vibrations in the range of 2900–2980 cm−1 and the CeOeC stretching between 1270 and 1050 cm−1 for PEG modifier are detected. Besides, the presence of a strong and sharp peak at higher wavenumber of 3425 cm−1 is recognized because of the stretching of hydroxyl groups of the PEG. A shift of C]O stretching to higher wavenumber and the formation of new ester bonding 1816 cm−1 seem to be certain reactions between carboxylic groups from surface of the GO

atmosphere at a heating rate of 10 °C/min to evaluate the thermal stability of biohybrids.

3. Results and discussion The AFM analyses of pure GO and PEGmGO materials were investigated and shown in Fig. 1. The thickness of the pure GO and PEGmGO were determined to be 2 and 2.2 nm, respectively. The higher thickness of the PEGmGO nanosheets compared to that of GO is assumed to the effectively covalent grafting of the PEG onto the surface GO surface. Which is in good agreement with previously reported literature [28]. The FT-IR spectra of GO, PEG, and PEGmGO material were presented in Fig. 2. The spectrum of GO shows the existence of some

Fig. 1. AFM analyses of (a, b) GO and (c, d) PEGmGO material. 653

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unmodified GO into the PLA matrix results in the increase of modulus value due to the high mechanical feature of such rigid filler (Fig. 4a) [42]. However, the unssuficent compatibility between GO and PLA matrix led to the reduction of the tensile stress and elongation. The tensile strength of the biohybrids was improved as compared to that of the PLAPEG sample consistent with the increase of the PEGmGO content from 0.1 to 1.2 phr. In this context, it was found that the tensile stress and modulus values of the PLAPEG/PEGmGO biohybrids increased with the increase of the PEGmGO content and they achieved the best performance at 0.3 phr of nanofiller (Fig. 4b and c). The use of higher PEGmGO content (≥0.6 phr) may lead to the formation of large intercalated tactoids and certain aggregation of GO structure, then negatively influencing on the mechanical behavior of biohybrid materials. The elonggation of the biohybrids did not significnatly change as compared to PLAPEG, but much higher than that of PLAPEG/0.3-GO material. The better elongation of the PLAPEG/PEGmGO compared to PLAPEG/0.3-GO was assumed to the effective plasticizing effect of the PEG and a consequence of the minor hindering effect from nanofiller on the mobility of matrix chains [41]. The good mechanical results for the PLAPEG/0.3-PEGmGO can be explained by the formation of interactions between PEGmGO nanosheets and PLA matrix, as seen in Fig. 4d, thereby promoting the uniform dispersion of GO into continuous PLA matrix. These results are in good agreement with the dispersion status of modified GO throughout the PLA matrix observed in previous XRD and following SEM and TEM analyses. The dispersion state of the PEGmGO nanofiller in PLA matrix is animated for the final properties of hybrid materials. Fig. 5 shows the fractured surfaces of the PLAPEG/0.3-GO, PLAPEG/0.3-PEGmGO, and PLAPEG/0.6-PEGmGO hybrids. In the case of the PLAPEG/0.3-GO hybrid, it can be seen that the fractured surface was quite rough along with occurrence of some pore structures, because GO nanosheets were pulled out during brittle fracturing and left irregular holes (Fig. 5a–c) [36]. The use of 0.3-PEGmGO for PLAPEG exhibits uniform and smooth fracture surface with more ductile feature, informing the good dispersion of the PEGmGO filler due to the improved interfacial interaction between PEGmGO and PLA matrix (Fig. 5d–f). Whereas, the relative roughness and presence of some small cracks along with crumples and wrinkles on the fracture surface in the PLAPEG/0.6-PEGmGO informed the use of higher GO amount can lead to the restacking phenomenon (Fig. 5g–i). TEM characterization can provide evaluable understanding about the dispersion state of PEGmGO filler in PLA polymer matrix (Fig. 6). The TEM micrograph of the PLAPEG/0.3-PEGmGO indicates that the modified GO nanosheets are well embedded and fully dispersed into the PLA matrix without phenomenon of aggregation or agglomeration. This result further indicates the good dispersion of nanofillers in the PLA matrix to produce an enhanced mechanical property compared to that of pure PLA or PLA filling with unmodified filler.

Fig. 2. FT-IR spectra of the GO, PEG, and PEGmGO material.

nanosheets and hydroxyl groups of PEG molecules. Particularly, the availability of a stronger peak at 1828 cm−1 was identified for C]O stretching of ester ring which was formed due to the formation of bonding between GO and PEG structure. XRD technique was used to characterize the crystal structure of the synthesized materials. Fig. 3a shows the XRD patterns of graphite flakes and GO material. Meanwhile the graphite shows a strong and sharp d (002) peak at 2θ of 26.5° consistent with a d-spacing of 3.35 Ao, GO presents an abroad peak at low 2θ of 10.6°, which matches with a dspacing of 8.3 Ao. This implies that numerous oxygen functional groups, such as epoxyl, hydroxyl, carbonyl, and carboxyl were successfully covalently attached on carbon structure after an oxidation process [47]. Certainly, the intercalation of water molecules may also a reason leading to extend interlayer spacing between carbon layers [48]. In the case of the PEGmGO material, the peak shifts to lower 2θ value of 6.2°, associated with d-spacing of 14.1 Ao. The significant increase in the dspacing of the PEGmGO compared to GO reflects the highly effective intercalation of the PEG molecule chains into the interlayer spacing of GO, as similarly seen by previous reports [7]. The presence of a peak at 2θ of 19.1° is due to the crystalline characteristic of d(120) plane from PEG modifier [7]. In the case of the PLA, the absence of crystalline peak in the surveyed 2θ range clearly indicates its amorphous feature (Fig. 3b). Considering XRD patterns for all PLAPEG/PEGmGO biohybrid materials, it can be seen the crystalline peak of carbon layer structure was completely disappeared, suggesting that the graphitic layer structure of the GO material was fully exfoliated to form homogeneous dispersion states in the hybrid structure. Fig. 4 shows the tensile properties of the pure PLA, PLAPEG/0.3-GO, and different PLAPEG/PEGmGO biohybrid materials. The addition of the

Fig. 3. XRD patterns of (a) graphite and GO; (b) PLA, PEGmGO, and biohybrids. 654

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Fig. 4. (a) Tensile stress, (b) modulus, and (c) elongation of materials: (1) PLAPEG, (2) PLAPEG/0.3-GO, (3) PLAPEG/0.1-PEGmGO, (4) PLAPEG/0.3-PEGmGO, (5) PLAPEG/0.6-PEGmGO, (6) PLAPEG/0.9-PEGmGO, and (7) PLAPEG/1.2-PEGmGO biohybrid; (d) illustration of mechanism interaction between GO, PEG and PLA matrix for enhanced mechanical properties.

Fig. 5. FE-SEM images of (a–c) for PLAPEG/0.3-GO, (d–f) PLAPEG/0.3-PEGmGO, and (g–i) PLAPEG/0.6-PEGmGO materials. 655

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Table 1 Thermal properties of PLA, PLAPEG, and PLAPEG/0.3-PEGmGO materials. Sample

Tg (oC)

Tm (oC)

ΔHf (J/g)

Tc (oC)

PLA PLAPEG PLAPEG/0.3-PEGmGO

61.9 52.3 51.4

149; 156 133 129.6

−25.4 −164.2 −168.1

105.4 – –

this phenomenon produces better mobility of PLA matrix and thereby reducing energy consumption during glass transition [52]. Besides, the slight decrease of Tg value (1 °C) and Tm value (1.9 °C) for PLAPEG/0.3PEGmGO as compared to PLAPEG was attributed to the further increase in the molecule mobility of PLA because the certain enhancement of the free volume caused by the presence of good dispersed nanofillers and the loosened molecular packing of the chains [53–55]. Furthermore, the melting enthalpy (ΔHf) of the PLAPEG and PLAPEG/0.3-PEGmGO biohybrid was found to be 6 times higher than that of pure PLA matrix. In another regard, there was a crystallization temperature (Tc) for pure PLA occurring at 105 °C, whereas no Tc value was available for the PLAPEG and biohybrid material. This observation indicated that PEG and PEGmGO plays a strong influence to prohibit the rearangement of PLA polymer chains, thereby specially reducing the crystallinity degree of PLA. The use of nanofillers based on graphene derivatives usually improve the thermal stability of polymer biohybrid because the physical barrier ability of fillers can effectively hinder the diffusion of degradation products, gases, and heat [56]. Thermal stability of the pure PLA, PLAPEG, and PLAPEG/0.3-PEGmGO biohybrid material was characterized by TGA (Fig. 8). The onset degradation temperature (Tonset) and midpoint degradation temperature (Tmidpoint) of the PLAPEG are shifted to lower temperatures of 470 and 498 °C, respectively, in the presence of PEG plasticizer, as similarly seen from previous reports [57]. In the case of the biohybrid, it can be found that the Tonset for the biohybrid started at 487 °C which was 4 °C higher than that for pure PLA (483 °C). Besides, the Tmidpoint value of the biohybrid was found at 519 °C, almost similar to pure PLA material, but much higher than that of the PLAPEG (499 °C). The appreciable enhancement of the Tonset for the PLAPEG/0.3-PEGmGO at very small PEGmGO amount implies that the PEGmGO nanosheets, which were homogeneously dispersed in the PLA matrix and well-interactedwith the PLA polymer chains, is sufficient to generate an effective network that absorbs supplied thermal energy during heating process and retards transfer of the degraded

Fig. 6. TEM images of PLAPEG/0.3-PEGmGO biohybrid material.

Fig. 7 shows the thermal properties of the graphite flakes, GO, PLA, PLAPEG, and PLAPEG/0.3-PEGmGO material. The corresponding results of thermal factors, including glass transition temperatures (Tg), melting temperature (Tm), crystalline temperature (Tc), and melting enthalpy (ΔHf) were presented in Table 1. The DSC measurement of graphite shows no change in range of temperature from 0 to 400 °C due to the high crystal quality of layer carbon structure (Fig. 7a). Meanwhile the GO appears one abroad endothermic peak in the temperature range from 50 to 100 °C because the absorbed H2O molecules on GO were eliminated under heating condition [49]. An exothermic peak recognized at higher temperature (240 °C) was ascribed to the reduction of GO [50,51]. The influence of PEG plasticizer and PEGmGO fillers on the thermal behavior of the PLA matrix was observed in Fig. 7b. The pure PLA polymer shows the Tg value at 61.9 °C and Tm values at 149 °C and 156 °C. Meanwhile, Tg and Tm values were found at 52.3 and 133 °C for PLAPEG and 51.4 and 129.6 °C for PLAPEG/0.3-PEGmGO biohybrid material, respectively. The significant decrease in Tg and Tm of the PLAPEG sample compared to that of pure PLA implies the good plasticization of PEG for PLA matrix, which leads to the increase in the mobility of PLA chains for the Tg reduction. In this regard, small PEG molecules can enter between the PLA polymer chains during the melt mixing procedure and generate physical interactions, such as hydrogen bonding and dipole-dipole communication, between atoms. As a result,

Fig. 7. DSC analyses for (a) graphite and GO; (b) PLA, PLAPEG, and PLAPEG/0.3-PEGmGObiohybrid material. 656

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Fig. 8. TGA analyses of the pure PLA, PLAPEG, and PLAPEG/0.3-PEGmGO biohybrid material.

products [58]. 4. Conclusion We sucessfully fabricated and studied the structure and properties of a biohybrid material based on the use of PEGmGO as a nanofiller for PLA matrix. It was found that PEG generated good interations with GO nanosheets through the formation of ester linkings, thereby easily intercalating into GO interlayers. The addition of low PEGmGO loading into PLA matrix produced some significant modulation in microstructure, mechanical performance, and thermal properties of the resulting biohybrid. The mechanical properties, such as modulus and tensile stress of the biohybrid were significantly improved. The Tg and Tm values of the biohybrid decreased as compared with pure PLA. Thermal stability of such biohybrid increased 7 °C at 0.3 phr of PEGmGO nanofiller. The obtained results for the PLAPEG/PEGmGO biohybrid suggest its potential for various bio-related applications in future. Acknowledgment Authors would like to acknowledge support from the Basic Science Research Program (2017R1D1A1B03028413) and (2016R1A6A1A03012069) through the National Research Foundation (NRF) funded by the Ministry of Education of Korea. This research was also supported by Faculty of Material Science, University of Science, Viet Nam National University Ho Chi Minh city, Viet Nam. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.compositesb.2018.12.152. References [1] Mao ND, Thanh TD, Thuong NT, Grillet AC, Kim NH, Lee JH. Enhanced mechanical and thermal properties of recycled ABS/nitrile rubber/nanofil N15 nanocomposites. Compos B Eng 2016;93:280–8. [2] Hamad K, Kaseem M, Deri F. Recycling of waste from polymer materials: an overview of the recent works. Polym Degrad Stabil 2013;98:2801–12. [3] Singh N, Hui D, Singh R, Ahuja IPS, Feo L, Fraternali F. Recycling of plastic solid waste: a state of art review and future applications. Compos B Eng 2017;115:409–22. [4] Chavalitpanya K, Phattanarudee S. Poly(lactic acid)/polycaprolactone blends compatibilized with block copolymer. Energy Procedia 2013;34:542–8. [5] Imre B, Pukánszky B. Compatibilization in bio-based and biodegradable polymer blends. Eur Polym J 2013;49:1215–33. [6] Nguyen DM, Vu TT, Grillet AC, Ha Thuc H, Ha Thuc CN. Effect of organoclay on morphology and properties of linear low density polyethylene and Vietnamese cassava starch biobased blend. Carbohydr Polym 2016;136:163–70.

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