Multifunctional and robust polyhydroxyalkanoate nanocomposites with superior gas barrier, heat resistant and inherent antibacterial performances

Chemical Engineering Journal 382 (2020) 122864

Contents lists available at ScienceDirect

Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej

Multifunctional and robust polyhydroxyalkanoate nanocomposites with superior gas barrier, heat resistant and inherent antibacterial performances

T

Pengwu Xua,b, Weijun Yanga, Deyu Niua, Manman Yua, Mingliang Dua, Weifu Donga, ⁎ Mingqing Chena, Pieter Jan Lemstraa,c, Piming Maa, a

The Key Laboratory of Synthetic and Biological Colloids, Ministry of Education, Jiangnan University, 1800 Lihu Road, Wuxi 214122, China Institute of Physics, University of Freiburg, Hermann-Herder-Street, 3, 79104 Freiburg, Germany c PlemPolco BV, De Zicht 11, 5502 HV Veldhoven, The Netherlands b

HIGHLIGHTS

GRAPHICAL ABSTRACT

was tailor-synthesized as • GO-g-LAQ multifunctional fillers for bio-based PHA.

heat resistant and anti• Barrier, bacterial performances of PHA films are achieved.

adhesion, condensed crys• Interfacial tals and superior strength were generated simultaneously.

designed PHA nanocomposites • The could be ideal for eco-friendly (food-) packaging.

ARTICLE INFO

ABSTRACT

Keywords: PHA Nanocomposites Antibacterial Barrier Mechanical properties

Bio-based and biocompatible materials such as polyhydroxyalkanoates (PHA) suffer from severe bacterial infection, poor oxygen barrier, low strength and poor heat resistance that restrict their wide applications especially in packaging areas. In this work, high-performance PHA nanocomposites with antibacterial properties are successfully obtained by compounding PHA with tailor-made long alkyl chain quaternary salt (LAQ) functionalized graphene oxide (GO-g-LAQ). The GO-g-LAQ could disperse in the PHA matrix uniformly and improve the interfacial adhesion between GO and PHA due to the hydrophobic nature of LAQ. As a result, PHA/GO-g-LAQ nanocomposites have the antibacterial rate of 99.9% against Gram-negative and Gram-positive bacteria without any leaching. The oxygen barrier is improved which is suggested by a significantly reduced oxygen permeation. This could be due to the condensed crystal structure of PHA and the impermeable property of GO sheets. The tensile strength and storage modulus at room temperature of the PHA films increased by 60% and 140%, respectively at an optimized concentration of GO-g-LAQ. The heat resistant performance of the PHA nanocomposites was simultaneously improved significantly due to the enhanced crystallization capability. Therefore, the well-designed PHA/GO-g-LAQ nanocomposites could be ideal candidates of functional materials for (food-) packaging applications.

⁎

Corresponding author. E-mail address: [email protected] (P. Ma).

https://doi.org/10.1016/j.cej.2019.122864 Received 25 May 2019; Received in revised form 18 August 2019; Accepted 16 September 2019 Available online 17 September 2019 1385-8947/ © 2019 Elsevier B.V. All rights reserved.

Chemical Engineering Journal 382 (2020) 122864

P. Xu, et al.

1. Introduction

its use as multifunctional nanofillers to simultaneously improve the mechanical, gas barrier, heat resistance and no-leaching antimicrobial properties of PHA for (food-) packaging. In this work, we attempt to graft long alkyl chain quaternary salts (LAQ) onto GO to obtain GO-g-LAQ nanohybrids via a coupling reaction and a free radical polymerization process as a multi-functional nanofiller, in consideration of the combined advantages of both GO and the hydrophobic and inherent antibacterial feature of LAQ. Tan et al. prepared GO/quaternary salts nanocomposites with an efficient antibacterial feature via π-π interactions [39,40]. Unlike inorganic antibacterial agents such as ZnO that would leach out the polymer matrix and subsequently reduce of the antibacterial ability [41], LAQ was regarded as an efficient non-leaching antibacterial agent [42–44]. The combined advantages are ideal for food packaging applications. Various contents of GO-g-LAQ nanohybrids have been blended with the medium-chain-length PHA to prepare PHA nanocomposite films by a casting technique. We assumed that the interfacial interaction between GO and PHA will be improved due to the long hydrophobic alkyl chain, i.e., grafted LAQ. Finally, the mechanical, barrier, thermal, antibacterial behaviors of the nanocomposite films are expected to be improved. Therefore, the primary objective of this work was to provide a facile method for preparing bio-based nanocomposites with superior mechanical properties, gas barrier, heat resistant and antibacterial property for (food-) packaging.

Most of polymer materials are non-biodegradable and produced from non-renewable fossil fuels, which result in serious environmental problems [1,2]. With the increasing concerns on the environmental sustainable development, there is a widespread consensus among industrial and academic community on developing sustainable biopolymer materials such as the natural carbohydrate derivatives starch, chitosan, cellulose and pectin [3–7]. In addition, there are many types of synthetic bio-based polymers including poly(glycolic acid) (PGA), poly(lactic acid) (PLA), poly(butylene succinate) (PBS), polyhydroxyalkanoate (PHA) etc., have been drawn tremendous attention [8–13]. Among them, PHA produced by the bacterial fermentation is considered as a promising material due to its preferable properties such as full biodegradability, non-cytotoxicity and high crystallinity [14]. Poly(3-hydroxybutyrate) (PHB) as the first generation products in PHA family has been widely studied. However, the disadvantages of PHB are also remarkable such as processability and high brittleness. Until now, the medium-chain-length-PHA copolymers poly(3-hydroxybutyrate-cohydroxyvalerate) (PHBV) and poly(3-hydroxybutyrate-co-hydroxyhexanoate) (PHBHHx), have been developed to improve the toughness and the processability of PHA, but physical strength, gas barrier and poor heat resistance are still insufficient [15,16]. Moreover, lacking of functionality such as antibacterial property further confined the application range of the PHA especially in packaging areas. Now PHAbased materials are mainly used in medical fields such as drug carriers, tissue engineering [17–19], and there are few papers to research the PHA-based composites to simultaneously overcome these problems for (food-) packaging. Lagarón et al. prepared the PHBV-silver nanoparticle composites with a strong antimicrobial activity but insufficient gas barrier and physical strength [20]. Nowadays, the nanotechnology presents a new opportunity to address these problems. Addition of nanofillers [21–30] such as carbon zinc oxide [21], nanotubes [23], boron nitride [24], nanocellulose [22,26,27], silver nanoparticles [20,26], nano-clays [25], graphene [28–31], has shown to be a powerful and efficient method to improve the above properties. Two-dimensional graphene oxide (GO) with a high aspect ratio, super barrier to most gases and excellent mechanical performance, was regarded as an efficient nanofiller for preparing high performance polymer nanocomposites [28–31]. However, nano-scale GO shows a poor dispersibility in the polymer matrix and as a result, unsatisfactory performance. Zhang et al. developed polyvinyl acetate (PVA) composites with GO as a nanofiller, showing increased tensile strength but a sharply decreased elongation at break, because the interfacial adhesion between GO filler and the PVA matrix was poor and GO sheets were agglomerated in the PVA matrix [32]. Hence, many physical and chemical modifications have been considered to improve the dispersion of GO into the polymer matrix [33–35]. Haddon et al. obtained covalently modified GO with alkylamine via the reaction between the acidic functional groups of GO and octadecylamine, leading to a stable dispersion in organic solutions [33]. Recently, Tran et al. synthesized the polyethylene glycol modified GO (PEG-GO) via the formation of ester linkings and then blended with PLA to prepare the bio-based PLA/PEG-GO nanocomposites. The nanocomposites displayed slightly improved tensile strength and thermal stability than PLA/PEG [36]. Ambrosio-Martin et al. developed PHBV-graphene nanocomposites by the high-energy ball milling method and graphene sheets have a good dispersion in PHBH matrix which was crucial for the improvement of barrier and tensile properties [37]. Chen et al. synthesized unsaturated PHA from microbial fermentation and then prepared PHA-graft-reduced GO nanocomposites with enhanced electricity conductivity and higher thermal degradation temperature through click reaction [38]. Therefore, it has been demonstrated by previous papers that GO can be exfoliated through a physical or chemical methods and dispersed in a polymer in good extent as a kind of efficient filler to give good mechanical properties. However, little attention has been paid on

2. Experimental section 2.1. Materials Polyhydroxyalkanoate (PHA, containing 93.1 mol% 3-hydroxybutyrate and 6.9 mol% of 3-hydroxyhexanoate) was bacterially synthesized with Mw of 5.9 × 105 g mol−1 and PDI of 2.5. Graphite (99.95%) was provided by The Six Element (changzhou) Materials Technology Co., Ltd China. The 2-(dimethylamino)ethyl methacrylate, 1-bromododecane (≥98%), benzoyl peroxide (BPO) (≥98%), 3-methacryloxypropyltrimethoxysilane (KH-570) (≥98%) and ethanol (≥99.5%) were supplied from Shanghai Aladdin Bio-Chem Technology Co., Ltd. 2.2. Synthesis of GO-KH570 GO was prepared by using Hummer’s method [45]. KH570 (10 ml) were first dispersed in a methanol/distilled water (45/5 ml) mixture under magnetic stirring to form homogeneous solution. Then, the solution was added to the GO/distilled water dispersion (10 mg/ml) under magnetic stirring in a silicone oil bath at 130 °C and the reaction was allowed for 12 h. The final product KH570-modified GO (GOKH570) was obtained by removing out the unreacted KH570 via centrifugation and extraction process. 2.3. Synthesis of long alkyl chain quaternary salts (LAQ) First, 2-(dimethylamino)ethyl methacrylate (20 mmol), 1-bromododecane (20 mmol), and ethanol (6 ml) were mixed together, and the reaction was maintained at 70 °C for 12 h. The LAQ was obtained via recrystallization in ethanol and a subsequent freeze-drying method. 2.4. Synthesis of GO-g-LAQ nanohybrids The GO-KH570 (0.5 g) was dispersed in 1-butanol (50 ml) at 80 °C under magnetic stirring and nitrogen atmosphere. Then BPO (8 mg) and LAQ (0.7 g) were added, and the reaction was continued for 24 h. The products were washed by distilled water for 3 times and then freezedried at −30 °C. Finally, the GO-g-LAQ nanohybrids were obtained. The synthesis processes are presented in Scheme 1. 2

Chemical Engineering Journal 382 (2020) 122864

P. Xu, et al.

(1) GO-KH570 preparation

(3) GO-g-LAQ preparation KH570:

coupling

GO

LAQ homopolymer: GO-KH570

KH570

copolymerization

(2) LAQ preparation

+ + + +

+ +

+

+ ++

quaternization C12H25-Br

+ + +

+ +

GO-g-LAQ

+ +

LAQ

Two-step chemical grafting reactions

+

HO HO HO

(1)

(3)

+ n

GO KH570

LAQ

GO-KH570

GO-g-LAQ

Scheme 1. Schematic diagram of the synthesis of GO-g-LAQ nanohybrids: (1) GO-KH570 preparation via the coupling reaction between GO and KH570, (2) LAQ preparation via the quaternization reaction and (3) GO-g-LAQ preparation via the free radical copolymerization of the C]C bond between LAQ and GO-KH570.

2.5. Preparation of PHA-based nanocomposite films

TEM coupled with JEM-2100F energy-dispersive X-ray spectroscopy (EDS). The spherulite morphology and the spherulite growth rate G were investigated by a polarizing optical microscope, POM (Axio Scope 1, Zeiss, Germany). Each sample was first held at 190 °C for 3 min and then cooled to 90 °C to observe the growth of PHA spherulites with crystallization time. Then, G was calculated by the equation G = dR/dt, where R is the radius of the spherulite and t is crystallization time. The calculation of G is shown in Fig. S1.

In detail, GO-g-LAQ was first dispersed in CHCl3 (50 ml) using ultrasonication. Then PHA was added under continuous stirring. The nanocomposite films were prepared by solvent-casting onto a glass culture dish. It has to remark that solvent-casting as a commonly used method is handy in laboratory because a limited amount of GO-g-LAQ nanohybrids was made, however melt processing such as film blowing should be preferred for large-scale production of PHAs films. The films were marked as PHA/GO-g-LAQn where n represents the weight ratio of GO-g-LAQ, for instance, PHA/GO-g-LAQ1 indicates 1.0 wt% of GO-gLAQ.

2.6.5. Differential scanning calorimetry (DSC) The crystallinity was calculated by a DSC 8000 analyzer (PerkinElmer, USA) under nitrogen at temperatures of −30 to 190 °C and a heating rate of 10 °C min−1.

2.6. Characterization methods

2.6.6. Wide angle X-ray diffraction (WAXD) WAXD spectrum was performed on an X-ray diffractometer (Bruker AXS D8, Germany) with scan angles from 5 to 50° at a scanning rate of 2°/min.

2.6.1. Fourier transform infrared spectroscopy (FTIR) FTIR spectra were obtained on a FTIR spectrometer (Nicolet 6700, US) in the wavenumber range of 400–4000 cm−1 with the resolution of 1 cm−1 and 128 scans.

2.6.7. Mechanical properties Tensile performance was measured using a tensile tester (Instron 5967, USA) at the crosshead speed of 10 mm min−1 according to the ISO 527 standard.

2.6.2. X-ray photoelectron spectroscopy (XPS) XPS measurements of GO and GO-g-LAQ were conducted on a Thermo Fisher Scientific 250Xi XPS microprobe instrument (Thermo Fisher Scientific, England). 2.6.3. Thermogravimetric analysis (TGA) TGA curves of GO, LAQ and GO-g-LAQ were performed on an instrument (TGA; Q500, TA Instruments) under nitrogen at a heating rate of 10 °C min−1.

2.6.8. Dynamic mechanical analysis (DMA) Dynamic mechanical properties were performed on a Q800 TA Instrument. The samples were tested under a nitrogen atmosphere from −30 to 100 °C at a frequency of 1 Hz. The constant amplitude was 20 μm and the temperature ramp was 1 °C/min.

2.6.4. Morphology The morphology of the composites was characterized on a scanning electron microscopy (S-4800, HITACHI, Japan) and JEOL-JEM-2100

2.6.9. Oxygen permeation (OP) OP of samples with the exposure area of 38.48 cm2 at 23 °C and 63.5% RH was obtained using an Oxygen Permeation Analyzer VAC-V2 3

P. Xu, et al.

Chemical Engineering Journal 382 (2020) 122864

(Labthink Instruments Co., LTD).

a

b

c

d

2.6.10. Antibacterial activity The killing efficiency against S. aureus and E. coli of PHA nanocomposites was evaluated by the standard plate count method [46–48]. The leaching behavior of GO-g-LAQ nanohybrids was evaluated using the typical zone of inhibition test [48,49]. The detailed procedures are addressed in Supporting information. 3. Results and discussion 3.1. Preparation and characterization of GO-g-LAQ Graphite sheets were successfully oxidized into GO by using Hummer method (WAXD spectrum of graphite and GO are provided as Supporting information in Fig. S2) [45]. GO has abundant carboxyl and hydroxyl groups at the edges and hydroxyl and epoxy groups on the surface [50,51], which greatly improve the chemical activity of graphite materials. In this work, KH570 was coupled to the surface of GO to form GO-KH570 via the coupled reaction between the acidic functional groups of GO and the siloxane functions of KH570. Then the long alkyl chain quaternary salts (LAQ) was synthesized by the quaternization reaction [52,53]. Finally, the GO-g-LAQ nanohybrid was synthesized via the free radical polymerization of the C]C bond between LAQ and GO-KH570. The chemical reaction diagram was shown in Scheme 1. FT-IR spectra were recorded to analyze the chemical structure of LAQ, GO, GO-KH570 and GO-g-LAQ, as shown in Fig. 1a. GO showed characteristic absorption peaks at 1619, 1731 and 3390 cm−1 (a broad peak) corresponding to CeC ring, C]O and OeH vibration, respectively. For GO-KH570, new bonds appeared at 1633 and 2850–2960 cm−1, corresponding to and C]C and CeH stretching. Meanwhile, the C]O stretch was shifted to 1720 cm−1 and the intensity increased as well, confirming the successful coupling reaction

C

2920

(3)

1480

1440

1720 1720

(4)

1633

1731 1619 C-C ring

Intensity (a.u.)

Transmittance (a.u.)

(2)

2850

C-N

(2) 1520

Br Si

between KH570 and GO. Furthermore, when LAQ was grafted to GOKH570, the peak of C]C bond (1633 cm−1) became almost invisible and a new bond at 1465 cm−1 assigned to CeN+ appeared (insert in Fig. 1a), consistent with the structure of LAQ, indicating that LAQ was grafted successfully on the surfaces of GO. Wide-scan XPS spectra of GO, GO-KH570 and GO-g-LAQ samples are shown in Fig. 1b, and the fitted C1s spectra of GO and GO-g-LAQ samples are also given in Fig. 1c and d. It could be observed from Fig. 1b that GO showed the signals corresponding to C1s and O1s. Compared with GO, GO-KH570 showed the new signals for Si2p and

b C=C C=O

O

Fig. 2. TEM images (the same scale) of (a) GO and (b) GO-g-LAQ, and EDS curves of (c) GO and (d) GO-g-LAQ.

(1)

CH2

GO-g-LAQ

GO

O

a (1)

C

GO GO-KH570 GO-g-LAQ

C1s

Br2d Si2p Si2s

O1s N1s

1720

3200

1800

1500 Wavenumbers (cm-1)

1200

0

600

C-C

C-C

C-O

(59.8%)

(38.4%)

C=O (1.8%)

290

(71.2%)

Intensity (a.u.)

Intensity (a.u.)

400

d

c

292

200

Binding Energy (eV)

C-O

C=O

(18.8%)

C-N

(5.3%)

(4.7%)

288

286

284

Binding Energy (eV)

292

282

290

288

286

284

Binding Energy (eV)

282

Fig. 1. (a) FT-IR spectra of (1) GO-g-LAQ, (2) GO-KH570, (3) GO and (4) LAQ, and (b) XPS wide-scan spectra of GO, GO-KH570 and GO-g-LAQ. C1s XPS spectra of (c) GO and (d) GO-g-LAQ.

4

Chemical Engineering Journal 382 (2020) 122864

P. Xu, et al.

a

b

100

LAQ

60 40

GO-g-LAQ

GO GO-g-LAQ LAQ

20

10

20

o

2θ ( )

30

0

40

a = 33.6

GO

100

200

300

400

500

Temperature (oC)

600

b = 47.1

plane

Weight (%)

002

Dg = 28.7 wt%

80

700

Fig. 3. (a) WAXD spectra and (b) TGA curves of GO, LAQ and GO-g-LAQ.

Si2s due to the coupling reaction between GO and KH570. GO-g-LAQ showed new signals for Br2d and N1s because of the grafting of LAQ onto GO. The C1s peak for GO were fitted into three peaks, i.e. C]O (288.6 eV), CeO (286.3 eV) and CeC (284.8 eV), respectively (Fig. 1c). In the case of GO-g-LAQ, one new peak emerged at 285.8 eV, correlated with the C-N bond. More importantly, the intensity of CeO bond decreased from 38.4 to 18.8%, while the intensity of CeC increased from 59.8 to 71.2% (Fig. 1d), suggesting that a considerable amount of LAQ was grafted onto the surface of GO. The TEM images of GO and GO-g-LAQ are shown in Fig. 2a and b, respectively. The GO sheet (1.5 um in length) exhibited a smooth surface, whereas GO-g-LAQ demonstrated a coarse surface. EDS characterization (Fig. 2c and d) elucidated that C/O ratio of GO was higher than that of GO-g-LAQ, and the new signals of Br and Si appeared, indicating the successful grafting of LAQ, in agreement with XPS results. Fig. 3a shows WAXD patterns of GO, LAQ, and GO-g-LAQ. The spectrum of GO exhibited an intense peak at 2θ = 10.5°, showing a 0.84 nm d-spacing (002 plane), which indicates that the oxidizing reaction increased the distance between graphitic interlayers (WAXD spectra of graphene are given in the Supporting Information) [34]. However, for GO-g-LAQ, the peak (0 0 2) almost disappeared, suggesting that GO became exfoliated after grafting LAQ. The similar results were also reported by Wu et al., who successfully grafted of polyepoxide onto GO [54]. Furthermore, the characteristic peaks of pure LAQ were also detected for GO-g-LAQ. These results also confirmed the successful grafting of LAQ onto the surface of GO. The GO, LAQ and GO-g-LAQ nanohybrids were further characterized by TGA (Fig. 3b). GO showed an initial decomposition temperature around 100 °C due to the water evaporation, and followed with a major decomposition around 220 °C that was ascribed to the decomposition of surface oxygenic functional groups. Finally, a 47.1 wt% of residual mass at 750 °C was detected. The LAQ sharply decomposed at 200–440 °C and almost completely decomposed, while the residual weight of GO-gLAQ was recorded as 33.6 wt% at 750 °C. The grafting degree of LAQ (Dg) could be estimated from TGA results according to following equation reported in our previous work [55]

Dg = 100

100 × a b

LAQ in the PHA matrix is much better than that of GO due to the long hydrophobic alkyl chain, greatly improving the interfacial adhesion between PHA and GO. Meanwhile, the photographs of GO and GO-gLAQ dispersed in chloroform are also shown in the inserted Fig. 4a and b, respectively. It can be observed that the GO was deposited in the bottom of vial, while GO-g-LAQ was uniformly dispersed in chloroform and formed a stable suspension. The microscopic morphologies of PHA/ GO5 and PHA/GO-g-LAQ5 nanocomposites were further studied by TEM, as shown in Fig. 4c and d. GO sheets obviously agglomerated while GO-g-LAQ showed a better separated sheet structure. These results suggested that GO-g-LAQ nanohybrids could be more compatible with PHA matrix than GO, due to the grafted long hydrophobic alkyl chain. The morphology of 5 wt% of GO and GO-g-LAQ incorporated within a PHA matrix was further examined by SEM. Fig. 5 displays the cryofractured surface of neat PHA, PHA/GO5, and PHA/GO-g-LAQ5 film, respectively. Neat PHA shows an extremely smooth surface (Fig. 5a), while PHA/GO5 exhibits a high rough surface, where some agglomerates could be seen (Fig. 5d), indicating a poor interfacial adhesion between PHA and GO. However, in the case of PHA/GO-g-LAQ5, it shows a homogeneous morphology and even unable to distinguish the GO phase from the PHA phase through SEM images. Therefore, TEM was used for better observation of the fine dispersed GO-g-LAQ. The TEM image (Fig. 5b′) is inserted in Fig. 5b, showing an exfoliated GO structure and a uniform dispersion, which is attributed to the improved interfacial adhesion between GO and PHA. POM was used to investigate the effect of GO-g-LAQ on the spherulite morphology of PHA nanocomposites. The spherulite images of PHA, PHA/GO5 and PHA/GO-g-LAQ5 at 90 °C are shown in Fig. 6. Neat PHA shows a large diameter spherulite (∼500 µm), indicating inferior crystallization behavior, which is consistent with the literature [56]. For PHA/GO nanocomposites, GO sheets agglomerated in the PHA matrix and could serve as nucleators to improve the overall crystallization speed of PHA, as shown in Fig. 6b. As a comparison, there are no aggregates in PHA/GO-g-LAQ, and smaller size of spherulites formed rapidly in 5 min and then crystalized completely in 20 min. To further quantify the crystallization of PHA, the nucleation density (N) was calculated as the following Eq. (2) [57].

(1)

where a and b are residual weights of GO-g-LAQ and GO from the TGA curves, respectively. In this study, the Dg was ca. 28.7 wt%.

N

3k (4 G )3

(2)

where Avrami constant k was obtained from the DSC results and the detailed process is shown in the Supporting information (Fig. S3). The growth rate G (3.7 µm min−1) of PHA spherulites is calculated from POM data (Fig. S1). It can be observed that The N values of PHA/GO and PHA/GO-g-LAQ increased from 0.5 cm−3 (PHA) to 92 cm−3 and 4700 cm−3, respectively (Fig. 7). Meanwhile, the DSC results indicate

3.2. Characterization of PHA/GO-g-LAQ nanocomposites PHA/GO-g-LAQ nanocomposite films were prepared by a solutioncasting method. The digital images of PHA/GO5 and PHA/GO-g-LAQ5 film are shown in Fig. 4a and b. Obviously, the dispersibility of GO-g5

Chemical Engineering Journal 382 (2020) 122864

P. Xu, et al.

Fig. 4. The digital photographs of (a) PHA/GO5 and (b) PHA/GO-g-LAQ5 film inserted with photos of (a′) GO and (b′) GO-g-LAQ in chloroform (30 mg/mL) and TEM images of (c) PHA/GO5 and (d) PHA/GO-g-LAQ5 nanocomposites.

Fig. 5. SEM images of the cryo-fractured surface of (a) PHA, (b) PHA/GO-g-LAQ5 and (c) PHA/GO5 composites. A TEM image of PHA/GO-g-LAQ5 as Fig. 5b’ is inset in Fig. 5b, and the green rectangle religion in 5c is enlarged as Fig. 5d for better visualization of GO agglomeration in the PHA/GO5 composites.

6

Chemical Engineering Journal 382 (2020) 122864

P. Xu, et al.

10

5

10

4

10

3

10

2

10

1

10

0

10

that the crystallinity (Xc) of PHA increased from 28.1% to 35.4%, when 5 wt% of GO-g-LAQ was present (Fig. S4). These results demonstrate that GO-g-LAQ nanohybrids greatly increase the nucleation density and the crystallinity of PHA, which would be beneficial to improve the barrier and physical performance. The oxygen permeation (OP) of the nanocomposite films is significant for packaging applications. The OP of PHA and PHA/GO-g-LAQ nanocomposite films was evaluated and the results are shown in Fig. 8, while the OP of PHA/GO-KH570 was shown in Fig. S5 as Supporting information. In general, it is considered as a promising barrier film for food packaging when the OP value is below 1.0 [11,58]. In this study, the neat PHA film showed an OP value of 1.45, suggesting a poor oxygen barrier property. After incorporation of 5 wt% of GO-g-LAQ, the OP value reduced significantly by 86% to 0.21, demonstrating a pronounced barrier performance. However, after incorporation of 5 wt% of GO-KH570, the OP value increased to 1.61, indicating even poorer barrier property. The mechanism of barrier improvement is usually attributed to increasing the pathway (tortuosity) of gas molecules to

4.7

-3

N (cm )

Fig. 6. Polarized optical microscopy images of (a) PHA, (b) PHA/GO5 and (c) PHA/GO-g-LAQ5 nanocomposites that isothermally crystallized at 90 °C for different crystallization times.

9.2

5

-1

PHA

PHA/GO

PHA/GO-g-LAQ

Fig. 7. The nucleation density N of PHA, PHA/GO5 and PHA/GO-g-LAQ5 nanocomposites at 90 °C.

Oxygen permeation (OP) (cm3 mm m-2 d atm)

a

b

2.0

GO-g-LAQ

1.6

PHA amorphous PHA crystal

O2

1.2 suitable for barrier food packaging

0.8 0.4 0.0

0

1

3

5

GO-g-LAQ content (wt %)

7

O2

Tortuosity pathways

Fig. 8. (a) Oxygen permeation of neat PHA and PHA/GO-g-LAQ nanocomposite films (b) illustration of gas barrier mechanism of PHA/GO-g-LAQ nanocomposite films.

7

Chemical Engineering Journal 382 (2020) 122864

P. Xu, et al.

104

b

PHA PHA/GO5

PHA PHA/GO5

0.16

PHA/GO-g-LAQ5

10

525 35.4% 103 795

15

20

25

0

30

20

30

32.2%

1240

0.04

28.1%

-20

17.0

10

0.08

1890

102

PHA/GO-g-LAQ5

0.12

3

16.5 0.1 15.6

Tan δ

Storage modulus (MPa)

a

Xc

35

20

40

60

Temperature (oC)

80

100

-20

0

20

40

60

Temperature ( oC)

80

100

Fig. 9. (a) Storage modulus (E’) and (b) Tan δ of PHA, PHA/GO5 and PHA/GO-g-LAQ5.

traverse the films [59–61]. There are three main factors to improve the barrier of nanocomposite films, i.e., i) the effect of nanofiller such as the microstructure and the aspect ratio, ii) the inherent performance of the polymer such as the crystallization behaviors, and iii) the interfacial interaction between nanofillers and matrix that could be the most significant factor for the barrier performance. Kyu et al. [34] have demonstrated that the OP value of the PVC/GO nanocomposites with a poor interfacial adhesion was higher than neat PVC, indicating lower barrier properties, while the oxygen barrier of the PVC/GO nanocomposites with a uniform dispersion was improved greatly. In this work, we designed GO-g-LAQ nanohybrids as suitable nanofillers with a two-dimensional nanostructure having a high aspect ratio. Meanwhile, the POM and DSC results have further demonstrated that GO-g-LAQ could be an efficient nucleator to enhance the crystal density of PHA matrix (Figs. 6 and 7), because of forming more condensed crystal structure and higher crystallinity (Fig. S4), resulting in a longer pathway of gas molecules. Importantly, GO-g-LAQ sheets could become exfoliated and disperse uniformly in the PHA matrix which could be observed obviously from the morphology (Fig. 5b and b′), illustrating an improved interfacial adhesion between GO-g-LAQ and PHA matrix. Therefore, the OP of PHA films was improved greatly and were obviously adequate for packing application. The illustration of gas barrier mechanism of the PHA/GO-g-LAQ nanocomposite films was shown in Fig. 8b. DMA measurements were performed to study the storage modulus (E′) and tan δ of the nanocomposites, as shown in Fig. 9. E′ of all samples decreased with increasing the temperature and followed the sequence of PHA/GO-g-LAQ5 > PHA/GO5 > PHA. For example, the E′ of PHA/GO5 at 25 °C increased from 795 to 1240 MPa, while that of

Stress (MPa)

Tensile strength (MPa)

PHA/GO-g-LAQ5

40

PHA/GO-g-LAQ3

PHA/GO-g-LAQ1

30

PHA/GO-g-LAQ7 PHA

20 10 0

0

4

8

Strain (%)

12

16

45 b

40

40

30

Elongation at break (%)

a

PHA/GO-g-LAQ5 increased to 1890 MPa (the inset in Fig. 10a). This improvement was due to the improved dispersion of GO-g-LAQ in PHA matrix. Mitra et al. also found that the E′ of polyimide/surface-imidized GO nanocomposites was 25–30% higher than unmodified GO due to the improved dispersion.[29] Interestingly, at a high temperature 75 °C, E′ of PHA decreased sharply to only 115 MPa, while that of PHA/GO-gLAQ still kept 525 MPa, demonstrating that GO-g-LAQ greatly improved heat resistance. The improvement was mainly attributed to the denser crystal structure and higher crystallinity of PHA/GO-g-LAQ nanocomposites. Moreover, the addition of GO-g-LAQ slightly increased the glass transition temperature (Tg) of PHA from 15.6 °C to 17.0 °C because GO-g-LAQ hindered the motion of PHA chains, as shown in Fig. 9b. Fig. 10 showed the stress-strain curves of PHA and PHA/GO-g-LAQ, elongation at break and tensile strength, respectively. The elongation at break and tensile strength of PHA/GO-KH570 were shown in Fig. S6. Neat PHA exhibited a tensile stress of ∼25 MPa and a low strain at break (∼4%), which are comparable to the values of commercial PHAs [62,63]. The tensile strength of our PHAs/GO-g-LAQ films increased from 24.8 MPa to 39.8 MPa with increasing the GO-g-LAQ content up to 5 wt%, which is higher than the reported results, e.g, Díez-Pascual et al. prepared PHA/ZnO nanocomposites with a tensile strength of 29.5 MPa when the content of ZnO is 4 wt% [62], while Turng et al. prepared PHA/nanofibrillated cellulose (NFC) nanocomposites with a tensile strength of 34.4 MPa when the content of NFC is 5 wt% [63]. On the other hand, the tensile strength of PHA/GO-KH570 film with 5 wt% GO-KH570 is only 24.2 MPa due to the poor interfacial adhesion between PHA and GO (Fig. S6). Neat PHA shows a low elongation at break because of its large size of spherulite. After incorporation of 1 wt% GOg-LAQ, the size of spherulite become much smaller resulting in higher

35

20

30

10

25 20

0

3 1 5 7 GO-g-LAQ content (wt %)

0

Fig. 10. (a) Stress-strain curves and (b) tensile strength and elongation at break of PHA/GO-g-LAQ nanocomposites. 8

Chemical Engineering Journal 382 (2020) 122864

P. Xu, et al.

a

b

100

80

ln{ln[(1-Wf)/WT]}

Weight (%)

80

70

60

60 260

40

270

280

PHA PHA/GO-g-LAQ1

20 0

300

400

PHA/GO-g-LAQ3

a

PHA/GO-g-LAQ5

a

-20

500

Fig. 11. (a) TGA curves and (b) Plots of ln ln

a

GO-g-LAQ

0

:84.8kJ mol-1

PHA/GO-g-LAQ1

a

:103.2kJ mol-1 :112.3kJ mol-1

:162.0kJ mol-1

-4

PHA/GO-g-LAQ5

Temperature (oC)

2

:76.7kJ mol-1

a

-2

PHA/GO-g-LAQ3

200

PHA

4

90

( ) 1

Wf

WT

toughness, thus higher elongation at break. However, the size of spherulite did not change so much with further increasing the GO-gLAQ content. On the other hand, GO-g-LAQ as a rigid reinforcing nanofiller would restrict the deformation of PHA matrix at higher loadings. Consequently, the elongation at break of PHA/GO-g-LAQ decreases when the content of GO-g-LAQ nanofillers is higher than 1 wt%. These results manifested that GO-g-LAQ also can greatly improve heat resistant performance and tensile strength of PHA. The thermal stability of PHA and PHA/GO-g-LAQ nanocomposites was analyzed by TGA as shown in Fig. 11a. Neat PHA decomposed in a narrow temperature range from 240 to 290 °C. When adding GO-g-LAQ nanohybrids, the thermal stability of PHA was improved. This improvement was supposed that the GO-g-LAQ nanohybrids might hinder the motion of PHA chains, thus increasing the activation energy of degradation (Ea) [64], which could be calculated from the following equation [65,66]:

vs

-10

0

10

of PHA and PHA/GO-g-LAQ nanocomposites.

ln ln

1

Wf WT

=

Ea 2 RTmax

(3)

where Wf is the final weight percent. WT is residual weight at T. Tmax is the temperature that the decomposition rate was the highest. = TTmax. Then, Ea could be calculated from the plots ofln ln

(

1

Wf

WT

)

vs

as given in Fig. 11b, where PHA/GO-g-LAQ showed a Ea of 162.0 kJ mol−1, higher than that of PHA (76.7 kJ mol−1), demonstrating that GO-g-LAQ could increase the thermal stability of PHA. Antimicrobial activity of PHA (the control sample) and PHA/GO-gLAQ nanocomposites against Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria was shown in Fig. 12. After 24 h incubation, the bacteria evidently aggregated on the film surface and formed larger colonies for the control sample, indicating a poor bactericidal ability (Fig. 12a and c). It has been demonstrated that GO does not antibacterial effects [67,68]. Compared to the control sample, PHA/GO-gLAQ sample showed significant bacterial reduction against both E. coli and S. aureus, indicating a remarkable antibacterial performance due to the presence of LAQ (the antibacterial rate is 99.9%), which caused disruption of bacteria cell membrane [69]. Therefore, the antibacterial ability of GO-g-LAQ in this work is even higher than or comparable to that of the traditional antibacterial agents, e.g., Díez-Vicente et al. prepared PHA/ZnO composites via solution casting method with an antibacterial rate of 97% after incorporation of 10 wt% ZnO [70], while Kang et al. prepared PHA/Ag nanocomposites with an antibacterial rate of 99.9% after incorporation of 1.0 wt% Ag [71]. It is known that the antimicrobial agents might leach out from polymer matrix, resulting in significant reduction of antibacterial ability and food security issues

Fig. 12. Formation of bacteria colonies: antibacterial activity of PHA (a and c) and PHA/GO-g-LAQ5 (b and d) composite towards E. coli and S. aureus.

Fig. 13. Inhibition zone test of PHA (left) and PHA/GO-g-LAQ5 (right, the black sample) composite towards E. coli (a) and S. aureus (b). 9

Chemical Engineering Journal 382 (2020) 122864

P. Xu, et al.

[72]. Inhibition zone test as a standard technique is widely used to qualitatively characterize leaching behaviors of antibacterial agent for packaging materials [48,49]. In the present work, typical zone-of-inhibition results against E. coli and S. aureus indicate no leaching of LAQ from the films (Fig. 13). Since the antibacterial component LAQ was polymerized into large molecules via free radical polymerization in this work and further chemically immobilized onto GO particles, thus it is not expected to leach out regardless of the type of intermedium. To support this remark, an overall migration experiment (the detailed procedures were shown in Supporting information) was performed using nonpolar isooctane and polar ethanol 10% (v/v) in aqueous solution respectively as food simulants according to EN-1186-1 [73]. As a result, the overall migration values of PHA/GO-g-LAQ films are almost equal to that of neat PHA films which accomplish the requirements for food packaging according to Commission Regulation No. 10/2011/EU [74], as shown in Table S1.

[2] R.A. Gross, B. Kalra, Biodegradable polymers for the environment, Science 297 (2002) 803–807. [3] M. Jonoobi, R. Oladi, Y. Davoudpour, K. Oksman, A. Dufresne, Y. Hamzeh, R. Davoodi, Different preparation methods and properties of nanostructured cellulose from various natural resources and residues: a review, Cellulose 22 (2015) 935–969. [4] K.H. Prashanth, R. Tharanathan, Chitin/chitosan: modifications and their unlimited application potential-an overview, Trends Food Sci. Technol. 18 (2007) 117–131. [5] W. Wu, C. Xu, Z. Zheng, B. Lin, L. Fu, Strengthened, recyclable shape memory rubber films with rigid filler nano-capillary Network, J. Mater. Chem. A 7 (2019) 6901–6910. [6] M. Makaremi, P. Pasbakhsh, G. Cavallaro, G. Lazzara, Y.K. Aw, S.M. Lee, S. Milioto, Effect of morphology and size of halloysite nanotubes on functional pectin bionanocomposites for food packaging applications, ACS Appl. Mater. Inter. 9 (2017) 17476–17488. [7] X. Wei, R. Bao, Z. Cao, W. Yang, B. Xie, M. 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. [8] D.S. Cha, M.S. Chinnan, Biopolymer-based antimicrobial packaging: a review, Crit. Rev. Food Sci. Nutr. 44 (2004) 223–237. [9] L.S. Dilkes-Hoffman, J.L. Lane, T. Grant, S. Pratt, P.A. Lant, B. Laycock, Environmental impact of biodegradable food packaging when considering food waste, J. Clean. Prod. 180 (2018) 325–334. [10] P. Xu, Q. Zeng, Y. Cao, P. Ma, W. Dong, M. Chen, Interfacial modification on polyhydroxyalkanoates/starch blend by grafting in-situ, Carbohyd. Polym. 174 (2017) 716–722. [11] K. Goh, J.K. Heising, Y. Yuan, H.E. Karahan, L. Wei, S. Zhai, J. Koh, N.M. Htin, F. Zhang, R. Wang, Sandwich-architectured poly (lactic acid)-graphene composite food packaging films, ACS Appl. Mater. Inter. 8 (2016) 9994–10004. [12] L. Fu, F. Wu, C. Xu, T. Cao, R. Wang, S. Guo, Anisotropic shape memory behaviors of polylactic acid/citric acid-bentonite composite with a gradient filler concentration in thickness direction, Ind. Eng. Chem. Res. 57 (2018) 6265–6274. [13] B. Wu, Q. Zeng, D. Niu, W. Yang, W. Dong, M. Chen, P. Ma, Design of supertoughened and heat-resistant PLLA/elastomer blends by controlling the distribution of stereocomplex crystallites and the morphology, Macromolecules 52 (2019) 1092–1103. [14] S. Malmir, B. Montero, M. Rico, L. Barral, R. Bouza, Morphology, thermal and barrier properties of biodegradable films of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) containing cellulose nanocrystals, Compos. Part. A Appl. S. 93 (2017) 41–48. [15] H. Xiang, W. Chen, Z. Chen, B. Sun, M. Zhu, Significant accelerated crystallization of long chain branched poly (3-hydroxybutyrate-co-3-hydroxyvalerate) with high nucleation temperature under fast cooling rate, Compos. Sci. Technol. 142 (2017) 207–213. [16] J.S. Barrett, A.A. Abdala, F. Srienc, Poly (hydroxyalkanoate) elastomers and their graphene nanocomposites, Macromolecules 47 (2014) 3926–3941. [17] X.Y. Xu, X.T. Li, S.W. Peng, J.F. Xiao, C. Liu, G. Fang, K.C. Chen, G.Q. Chen, The behaviour of neural stem cells on polyhydroxyalkanoate nanofiber scaffolds, Biomaterials 31 (2010) 3967–3975. [18] V.C. Kalia, S. Ray, S.K. Patel, M. Singh, G.P. Singh, the dawn of novel biotechnological applications of polyhydroxyalkanoates, Biotechnological Applications of Polyhydroxyalkanoates, Springer, 2019, pp. 1–11. [19] N. Pramanik, S. Bhattacharya, T. Rath, J. De, A. Adhikary, R.K. Basu, P.P. Kundu, Polyhydroxybutyrate-co-hydroxyvalerate copolymer modified graphite oxide based 3D scaffold for tissue engineering application, Mat. Sci. Eng. C-Mater. 94 (2019) 534–546. [20] J. Castro-Mayorga, A. Martínez-Abad, M. Fabra, C. Olivera, M. Reis, J. Lagarón, Stabilization of antimicrobial silver nanoparticles by a polyhydroxyalkanoate obtained from mixed bacterial culture, Int. J. Biol. Macromol. 71 (2014) 103–110. [21] J.L. Castro-Mayorga, M.J. Fabra, A.M. Pourrahimi, R.T. Olsson, J. Lagaron, The impact of zinc oxide particle morphology as an antimicrobial and when incorporated in poly (3-hydroxybutyrate-co-3-hydroxyvalerate) films for food packaging and food contact surfaces applications, Food Bioprod. Process. 101 (2017) 32–44. [22] P. Ma, L. Jiang, P. Xu, W. Dong, M. Chen, P.J. Lemstra, Rapid stereocomplexation between enantiomeric comb-shaped cellulose-g-poly (l-lactide) nanohybrids and poly (d-lactide) from the melt, Biomacromolecules 16 (2015) 3723–3729. [23] C. Xu, Z. Qiu, Crystallization behavior and thermal property of biodegradable poly (3-hydroxybutyrate)/multi-walled carbon nanotubes nanocomposite, Polym. Adv. Technol. 22 (2011) 538–544. [24] J.A.S. Puente, A. Esposito, F. Chivrac, E. Dargent, Effect of boron nitride as a nucleating agent on the crystallization of bacterial poly (3-hydroxybutyrate), J. Appl. Polym. Sci. 128 (2013) 2586–2594. [25] A.M. El-Hadi, Investigation of the effect of nano-clay type on the non-isothermal crystallization kinetics and morphology of poly (3 (r)-hydroxybutyrate) PHB/clay nanocomposites, Polym. Bull. (Berlin) 71 (2014) 1449–1470. [26] H. Yu, B. Sun, D. Zhang, G. Chen, X. Yang, J. Yao, Reinforcement of biodegradable poly (3-hydroxybutyrate-co-3-hydroxyvalerate) with cellulose nanocrystal/silver nanohybrids as bifunctional nanofillers, J. Mater. Chem. B 2 (2014) 8479–8489. [27] Q. Yu, W. Yang, Q. Wang, W. Dong, M. Du, P. Ma, Functionalization of cellulose nanocrystals with γ-MPS and its effect on the adhesive behavior of acrylic pressure sensitive adhesives, Carbohydr. Polym. (2019). [28] M. Larsson, C.J. Hetherington, R. Wallenberg, P. Jannasch, Effect of hydrophobically modified graphene oxide on the properties of poly (3-hydroxybutyrateco-4-hydroxybutyrate), Polymer 108 (2017) 66–77. [29] M. Yoonessi, Y. Shi, D.A. Scheiman, M. Lebron-Colon, D.M. Tigelaar, R. Weiss,

4. Conclusions Long alkyl chain quaternary (LAQ) salt was successfully grafted onto graphene oxide to obtain GO-g-LAQ nanohybrids as a functionalized nanofiller by free radical polymerization of vinyl bond of LAQ on the surface of GO. Then, a series of PHA/GO-g-LAQ nanocomposite films were prepared by a solvent cast method. The results showed that the interfacial adhesion between GO and PHA matrix and the dispersibility of GO was improved greatly by the incorporation of GO-gLAQ, inducing a remarkable enhancement of crystallization behaviors of PHA. Thus, the antimicrobial ability, gas barrier, heat resistant and mechanical properties of the resulted PHA/GO-g-LAQ nanocomposite films were significantly improved, indicating that functionalized GO with the long alkyl chain of LAQ was beneficial to enhance the properties of PHA. For example, the oxygen permeation of the PHA films was reduced by 86%, while the tensile strength (room temperature) and storage modulus (100 °C) of the PHA films was increased from 25 MPa and 40 MPa to 40 MPa and 285 MPa, respectively, after incorporation of 5 wt% of GO-g-LAQ. Moreover, an antibacterial activity of 99.9% of the PHA/GO-g-LAQ nanocomposites without any leaching of antibacterial agent was obtained. Therefore, this work may provide a facile and highefficiency solution to design the high-performance PHA-based nanocomposites that could be promising candidates for multi-functional packaging materials in wide application ranges. Acknowledgements This work is supported by the National Natural Science Foundation of China (51573074, 51873082), the Excellent Youth Natural Science Foundation of Jiangsu Province (BK20170053), the Fundamental Research Funds for the Central Universities (JUSRP21909), the MOE & SAFEA 111 Project (B13025) and the scholarship from China Scholarship Council (201806790039). Appendix A. Supplementary data The growth rate G of PHA, WAXD spectrum of graphite and GO, Avrami curves and the crystallinity upon first melting DSC curves of PHA, PHA/GO5 and PHA/GO-g-LAQ5, the oxygen permeation and mechanical properties of PHA/GO-KH570, the detailed method of the antibacterial activity test and overall migration test. Supplementary data to this article can be found online at https://doi.org/10.1016/j.cej. 2019.122864. References [1] C.M. Rochman, M.A. Browne, B.S. Halpern, B.T. Hentschel, E. Hoh, H.K. Karapanagioti, L.M. Rios-Mendoza, H. Takada, S. Teh, R.C. Thompson, Policy: classify plastic waste as hazardous, Nature 494 (2013) 169.

10

Chemical Engineering Journal 382 (2020) 122864

P. Xu, et al.

[30]

[31] [32] [33] [34] [35] [36]

[37]

[38] [39] [40]

[41] [42]

[43]

[44] [45] [46] [47] [48] [49] [50] [51]

(2011) 7292–7295. [52] J. Zhao, W. Millians, S. Tang, T. Wu, L. Zhu, W. Ming, Self-stratified antimicrobial acrylic coatings via one-step UV curing, ACS Appl. Mater. Inter. 7 (2015) 18467–18472. [53] X. Cheng, T. Qu, C. Ma, D. Xiang, Q. Yu, X. Liu, Bioactive mono-dispersed nanospheres with long-term antibacterial effects for endodontic sealing, J. Mater. Chem. B 5 (2017) 1195–1204. [54] Y. Wu, P. Jia, L. Xu, Z. Chen, L. Xiao, J. Sun, J. Zhang, Y. Huang, C.W. Bielawski, J. Geng, Tuning the surface properties of graphene oxide by surface-initiated polymerization of epoxides: an efficient method for enhancing gas separation, ACS Appl. Mater. Inter. 9 (2017) 4998–5005. [55] P. Xu, Y. Cao, B. Wu, P. Ma, W. Dong, H. Bai, H. Zhang, H. Zhu, M. Chen, Effects of modified nanocrystalline cellulose on the hydrophilicity, crystallization and mechanical behaviors of poly (3-hydroxybutyrate-co-3-hydroxyhexanoate), New J. Chem. 42 (2018) 11972–11978. [56] P.W. Xu, Y. Cao, P. Lv, P.M. Ma, W.F. Dong, H.Y. Bai, W. Wang, M.L. Du, M.Q. Chen, Enhanced crystallization kinetics of bacterially synthesized poly(3-hydroxybutyrate-co-3-hydroxyhexanate) with structural optimization of oxalamide compounds as nucleators, Polym. Degrad. Stab. 154 (2018) 170–176. [57] Y. He, Y. Inoue, α-Cyclodextrin-enhanced crystallization of poly (3-hydroxybutyrate), Biomacromolecules 4 (2003) 1865–1867. [58] A.J. Svagan, A. Åkesson, M. Cárdenas, S. Bulut, J.C. Knudsen, J. Risbo, D. Plackett, Transparent films based on PLA and montmorillonite with tunable oxygen barrier properties, Biomacromolecules 13 (2012) 397–405. [59] Y. Cui, S. Kundalwal, S. Kumar, Gas barrier performance of graphene/polymer nanocomposites, Carbon 98 (2016) 313–333. [60] H. Bai, C. Huang, H. Xiu, Q. Zhang, H. Deng, K. Wang, F. Chen, Q. Fu, Significantly improving oxygen barrier properties of polylactide via constructing parallel-aligned shish-kebab-like crystals with well-interlocked boundaries, Biomacromolecules 15 (2014) 1507–1514. [61] P.J. Lemstra, Confined polymers crystallize, Science 323 (2009) 725–726. [62] A.M. Díez-Pascual, A.L. Diez-Vicente, ZnO-reinforced poly (3-hydroxybutyrate-co3-hydroxyvalerate) bionanocomposites with antimicrobial function for food packaging, ACS Appl. Mater. Inter 6 (2014) 9822–9834. [63] Y. Srithep, T. Ellingham, J. Peng, R. Sabo, C. Clemons, L.S. Turng, S. Pilla, Melt compounding of poly (3-hydroxybutyrate-co-3-hydroxyvalerate)/nanofibrillated cellulose nanocomposites, Polym. Degrad. Stab. 98 (2013) 1439–1449. [64] M. Zhang, H. Yan, L. Yuan, C. Liu, Effect of functionalized graphene oxide with hyperbranched POSS polymer on mechanical and dielectric properties of cyanate ester composites, RSC Adv. 6 (2016) 38887–38896. [65] L. Wei, A.G. McDonald, N.M. Stark, Grafting of bacterial polyhydroxybutyrate (PHB) onto cellulose via in situ reactive extrusion with dicumyl peroxide, Biomacromolecules 16 (2015) 1040–1049. [66] H.H. Horowitz, G. Metzger, A new analysis of thermogravimetric traces, Anal. Chem. 35 (1963) 1464–1468. [67] O.N. Ruiz, K.A.S. Fernando, B. Wang, Graphene oxide: a nonspecific enhancer of cellular growth, ACS Nano 5 (2011) 8100–8107. [68] W.P. Xu, L.C. Zhang, J.P. Li, Facile synthesis of silver@ graphene oxide nanocomposites and their enhanced antibacterial properties, J. Mater. Chem. 12 (2011) 4593–4597. [69] S. Wessels, H. Ingmer, Modes of action of three disinfectant active substances: a review, Regul. Toxicol. Pharm. 67 (2013) 456–467. [70] A. Díez-Pascual, A. Díez-Vicente, Poly (3-hydroxybutyrate)/ZnO bionanocomposites with improved mechanical, barrier and antibacterial properties, Int. J. Mol. Sci. 15 (2014) 10950–10973. [71] Z.C. Xing, W.P. Chae, J.Y. Baek, M.J. Choi, Y. Jung, I.K. Kang, In vitro assessment of antibacterial activity and cytocompatibility of silver-containing PHBV nanofibrous scaffolds for tissue engineering, Biomacromolecules 11 (2010) 1248–1253. [72] S. Benavides, R. Villalobos-Carvajal, J. Reyes, Physical, mechanical and antibacterial properties of alginate film: effect of the crosslinking degree and oregano essential oil concentration, J. Food Eng. 110 (2012) 232–239. [73] EN-1186-1, Materials and articles in contact with foodstuffs. In: plastics: part 1. guide to the selection of conditions and test methods for overall migration, CEN, European committee for standardization: Brussels, Belgium, 2002. [74] Commission regulation No 10/2011/EU, Commission regulation on plastic materials and articles intended to come into contact with foodstuffs, In: official journal of European communities, EUR-OP: Brussels, Belgium, 2011.

M.A. Meador, Graphene polyimide nanocomposites; thermal, mechanical, and hightemperature shape memory effects, ACS Nano 6 (2012) 7644–7655. Y. Zhang, S.J. Park, Influence of the nanoscaled hybrid based on nanodiamond@ graphene oxide architecture on the rheological and thermo-physical performances of carboxylated-polymeric composites, Compos. Part A-Appl. S. 112 (2018) 356–364. Y. Zhang, U.R. Cho, Enhanced thermo-physical properties of nitrile-butadiene rubber nanocomposites filled with simultaneously reduced and functionalized graphene oxide, Polym. Compos. 39 (2018) 3227–3235. X. Zhao, Q. Zhang, D. Chen, P. Lu, Enhanced mechanical properties of graphenebased poly (vinyl alcohol) composites, Macromolecules 43 (2010) 2357–2363. S. Niyogi, E. Bekyarova, M.E. Itkis, J.L. McWilliams, M.A. Hamon, R.C. Haddon, Solution properties of graphite and graphene, J. Am. Chem. Soc. 128 (2006) 7720–7721. K.W. Lee, J.W. Chung, S. Kwak, Flexible poly (vinyl chloride) nanocomposites reinforced with hyperbranched polyglycerol-functionalized graphene oxide for enhanced gas barrier performance, ACS Appl. Mater. Inter. 9 (2017) 33149–33158. S.H. Shim, K.T. Kim, J.U. Lee, W.H. Jo, Facile method to functionalize graphene oxide and its application to poly (ethylene terephthalate)/graphene composite, ACS Appl. Mater. Inter. 4 (2012) 4184–4191. N.D. Mao, H. Jeong, T.K.N. Nguyen, T.M.L. Nguyen, T.V.V. Do, C.N.H. Thuc, P. Perré, S.C. Ko, H.G. Kim, D.T. Tran, Polyethylene glycol functionalized graphene oxide and its influences on properties of poly (lactic acid) biohybrid materials, Compos. Part B: Eng. 161 (2019) 651–658. J. Ambrosio-Martín, G. Gorrasi, A. Lopez-Rubio, M.J. Fabra, L.C. Mas, M.A. LópezManchado, J.M. Lagaron, On the use of ball milling to develop poly (3-hydroxybutyrate-co-3-hydroxyvalerate)-graphene nanocomposites (II)-Mechanical, barrier, and electrical properties, J. Appl. Polym. Sci. 132 (2015). H. Yao, L.P. Wu, G.Q. Chen, Synthesis and characterization of electroconductive PHA-graft-graphene nanocomposites, Biomacromolecules 20 (2019) 645–652. X. Ye, X. Qin, X. Yan, J. Guo, L. Huang, D. Chen, S. Tan, X. Cai, π–π conjugations improve the long-term antibacterial properties of graphene oxide/quaternary ammonium salt nanocomposites, Chem. Eng. J. 304 (2016) 873–881. X. Ye, J. Feng, J. Zhang, X. Yang, X. Liao, Q. Shi, S. Tan, Controlled release and long-term antibacterial activity of reduced graphene oxide/quaternary ammonium salt nanocomposites prepared by non-covalent modification, Colloids Surf. B 149 (2017) 322–329. E. Tang, S. Dong, Preparation of styrene polymer/ZnO nanocomposite latex via miniemulsion polymerization and its antibacterial property, Colloid Polym. Sci. 287 (2009) 1025–1032. T. Shalev, A. Gopin, M. Bauer, R.W. Stark, S. Rahimipour, Non-leaching antimicrobial surfaces through polydopamine bio-inspired coating of quaternary ammonium salts or an ultrashort antimicrobial lipopeptide, J. Mater. Chem. 22 (2012) 2026–2032. S. Ye, P. Majumdar, B. Chisholm, S. Stafslien, Z. Chen, Antifouling and antimicrobial mechanism of tethered quaternary ammonium salts in a cross-linked poly (dimethylsiloxane) matrix studied using sum frequency generation vibrational spectroscopy, Langmuir 26 (2010) 16455–16462. C. Wu, K. Schwibbert, K. Achazi, P. Landsberger, A. Gorbushina, R. Haag, Active antibacterial and antifouling surface coating via a facile one-step enzymatic crosslinking, Biomacromolecules 18 (2016) 210–216. D.C. Marcano, D.V. Kosynkin, J.M. Berlin, A. Sinitskii, Z. Sun, A. Slesarev, L.B. Alemany, W. Lu, J.M. Tour, Improved synthesis of graphene oxide, ACS Nano 4 (2010) 4806–4814. G. He, Y. Wu, Y. Zhang, Y. Zhu, Y. Zheng, Addition of Zn to the ternary Mg-Ca-Sr alloys significantly improves their antibacterial properties, J. Mater. Chem. B 3 (2015) 6676–6689. J. Guo, Q. Xu, R. Shi, Z. Zheng, H. Mao, F. Yan, Polyanionic antimicrobial membranes: an experimental and theoretical study, Langmuir 33 (2017) 4346–4355. R. Chen, T. Li, Q. Zhang, Z. Ding, S. Zhang, W. Ming, Design of polyurethane acrylic antimicrobial films via one-step UV curing, New J. Chem. 41 (2017) 9762–9768. N. Beyth, I. Yudovin-Farber, R. Bahir, A.J. Domb, E.I. Weiss, Antibacterial activity of dental composites containing quaternary ammonium polyethylenimine nanoparticles against Streptococcus mutans, Biomaterials 27 (2006) 3995–4002. H. Kim, A. Abdala, C.W. Macosko, Graphene/polymer nanocomposites, Macromolecules 43 (2010) 6515. D.R. Dreyer, H.P. Jia, A.D. Todd, J. Geng, C.W. Bielawski, Graphite oxide: a selective and highly efficient oxidant of thiols and sulfides, Org. Biomol. Chem. 9

11