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Utilization of peanut husks as a filler in aliphatic–aromatic polyesters: Preparation, characterization, and biodegradability
Polymer Degradation and Stability 97 (2012) 2388e2395
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Utilization of peanut husks as a filler in aliphaticearomatic polyesters: Preparation, characterization, and biodegradability Chin-San Wu* Department of Chemical and Biochemical Engineering, Kao Yuan University, Kaohsiung County 82101, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history: Received 20 May 2012 Received in revised form 12 July 2012 Accepted 21 July 2012 Available online 11 August 2012
The biodegradability, morphology, and mechanical properties of composite materials made of poly(butylene adipate-co-terephthalate) (PBAT) and peanut husks (PH) were evaluated. Composites containing maleic anhydride-grafted PBAT (PBAT-g-MA/PH) exhibited noticeably superior mechanical properties because of greater compatibility between the two components. The dispersion of PH in the PBAT-g-MA matrix was highly homogeneous as a result of ester formation between the anhydride carboxyl groups of PBAT-g-MA and hydroxyl groups in PH and the consequent creation of branched and cross-linked macromolecules. Each composite was subjected to biodegradation tests in Aminobacter aminovorans compost. Morphological observations indicated severe disruption of film structure after 60 days of incubation, and both the PBAT and the PBAT-g-MA/PH composite films were eventually completely degraded. Water resistance of PBAT-g-MA/PH was higher than that of PBAT/PH, although the weight loss of composites buried in A. aminovorans compost indicated that both were biodegradable, even at high levels of PH substitution. The PBAT-g-MA/PH films were more biodegradable than those made of PBAT, implying a strong connection between these characteristics and biodegradability. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Biodegradable Polyesters Peanut husks Composites
1. Introduction It is becoming increasingly difficult to find disposal sites for plastic-based materials [1e3]. The development of renewable and green biodegradable materials has been a trend in environmental projects in recent years. Green composites are gradually replacing general plastics to achieve the goal of environmental sustainability [4e6]. In recent years, because of economic and environmental concerns such as waste management and carbon emissions, the use of biodegradable polyesters from renewable or fossil sources, or a combination of both, has gained research and industry attention [7,8]. The biodegradation of poly(butylene adipate-coterephthalate) (PBAT) and the resulting aliphatic-co-aromatic copolyester has been investigated [9,10]. To obtain biodegradable polymers having satisfactory mechanical properties, many researchers have begun to synthesize aliphatic-co-aromatic copolyesters [11,12]. PBAT biodegrades into naturally-occurring products within only a few years, in contrast to conventional plastics like polystyrene (PS) and polypropylene (PP) that require hundreds or even thousands of years to biodegrade. The degradation of PBAT may result
* Fax: þ886 7 6077788. E-mail address: [email protected]. 0141-3910/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.polymdegradstab.2012.07.027
from chain scission and the generation of free radicals in the aromatic structures [13,14]. Because of its excellent biocompatibility and physical properties, PBAT and its copolymers have been proposed for use in various biomaterial applications, and several commercially successful applications have emerged [15,16]. PBAT begins to degrade after only a few days in soil and enzymatic environments [17,18]. Unfortunately, widespread commercialization of PBAT has been limited because its production is both complex and expensive. However, these limitations can potentially be overcome by using PBAT composites. The composites combine PBAT with polymers and natural compounds found in biodegradable agricultural residues such as rice husks, rice straw, and peanut husks (PH). These residues are abundant, inexpensive, renewable, and fully biodegradable [19,20]. Xiao et al. [21] explored the use of underutilized byproducts from both agricultural and industrial production to reduce environmental pollution. Composites of PBAT and agricultural residues would likely be less expensive than pure PBAT, and their biodegradability and mechanical properties can be adjusted by varying the composition [22]. There is also growing interest in exploiting renewable resources as raw materials for the production of commercially-useful biodegradable plastics [23]. Several researchers have successfully developed composites of thermoplastic polymers with lignin derived from pecan shell and peanut hull flour [24]. PH is an abundant agricultural resource. Although cellulose fibers in plastic
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composites can yield many desirable properties, fiber dispersion and fiber-matrix compatibility remains problematic [25]. Additionally, although composites with high fiber contents are inexpensive, their high viscosities and other undesirable rheological properties during processing have limited the application of these materials. This report describes a systematic investigation of the mechanical properties and biodegradability of PH composites made with PBAT and maleic anhydride-grafted-grafted PBAT (PBATg-MA). The composites were characterized using Fourier transform infrared spectroscopy (FTIR), 13C nuclear magnetic resonance (NMR) spectroscopy, and X-ray diffraction (XRD) to identify bulk structural changes induced by the maleic anhydride moiety. Water absorption and weight loss of blends exposed to Aminobacter aminovorans compost were also measured as indicators of water resistance and biodegradability.
Recovered PH samples obtained prior to grinding consisted of a mixture of fine pale-yellow fragments up to 0.5e3 cm long. For utilizing, the fragments were processed as follows: Firstly, crude PH was dried at 50e60 C under vacuum for 2 days. Then the product was ground in a high-speed rotary grinder (Yowlin Industrial Co. Ltd., Taiwan) at 90 s for six times and was vacuum-dried at 50e60 C for 2 days again. Thereafter, the crushed PH was passed through 200-mesh sieve to have PH powder at about 10e40 mm and was purified by immersing 60 g of PH powder in 1000 mL of distilled water for 2 days to remove any water-soluble components. Eventually, the PH samples were further air-dried for 2 days at 50e60 C and vacuum-dried at 105 C for at least 6 h to have the moisture content fall to 5.0 0.2%. The entire processing procedures can also be seen in Scheme 2.
2. Experimental
2.4. Composite preparation
2.1. Materials
Prior to composite fabrication, PH samples were washed with acetone and dried in an oven at 105 C for 24 h. Composites were prepared in a “Plastograph” 200-Nm Mixer W50EHT with a blade rotor (Brabender, Dayton, USA). The composites were mixed between 120 and 130 C for 20 min at a rotor speed of 50 rpm. Samples were prepared with mass ratios of PH to PBAT or to PBATg-MA of 10/90, 20/80, 30/70, and 40/60. Residual MA in the PBAT-gMA reaction mixture was removed via acetone extraction prior to the preparation of PBAT-g-MA/PH. After mixing, the composites were pressed into thin plates with a hot press and placed in a dryer for cooling. These thin plates were cut to standard sample dimensions for further characterization.
PBAT resins were purchased from BASF Corporation (Florham Park, USA). Maleic anhydride (MA), obtained from Sigma (St. Louis, USA), was purified before use by recrystallization from chloroform. Benzoyl peroxide (BPO; Sigma) was used as an initiator and was purified by dissolution in chloroform and reprecipitation in methanol. A PH composed of 70e79% cellulose and 10.1% hemicelluloses was obtained from the Council of Agriculture Executive Yuan (Taiwan). The levels of protein, lipid and ash in the PH were negligible.
2.3. Peanut husk (PH) processing
2.2. PBAT-g-MA copolymer 2.5. NMR/FTIR/XRD analyses The grafting reaction of MA onto PBAT is illustrated in Scheme 1. In preliminary experiments using tetrahydrofuran as the solvent, different amounts of BPO and MA were used in the grafting reaction at 45 2 C and 60 rpm for 10 h. The grafted product (4 g) was dissolved in 200 mL of refluxing tetrahydrofuran at 45 2 C, and the hot solution was filtered through several layers of cheesecloth. The cheesecloth was washed with 600 mL of acetone to remove the tetrahydrofuran-insoluble, unreacted maleic anhydride, and the remaining product was dried in a vacuum oven at 80 C for 24 h. The tetrahydrofuran-soluble component of the filtrate was extracted five times using 600 mL of cold acetone for each extraction. A grafting percentage of approximately 1.06 wt% was determined by titration [26]. BPO and MA loadings were maintained at 0.3 and 10 wt%, respectively.
Solid-state 13C NMR was performed with an AMX-400 NMR spectrometer, and spectra were obtained at 100 MHz under crosspolarization while spinning at the magic angle. Power decoupling conditions were set with a 90 pulse and a 4-s cycle time. Fourier transform infrared spectrometry (FTIR; FTS-7PC type; Bio-Rad, Hercules) was used to investigate the grafting reaction of MA onto PBAT and to verify ester bond formation between the anhydride carboxyl groups in PBAT-g-MA with the hydroxyl groups of PH. Samples subjected to FTIR analysis were ground into fine powders in a milling machine and pressed into pellets with potassium bromide. XRD diffractograms were recorded using a D/ max 3-V X-ray diffractometer (Rigaku, Tokyo, Japan) with a Cu target and Ka radiation at a scanning rate of 2 /min.
Scheme 1. Grafting reaction of MA onto PBAT.
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Scheme 2. Modification of PBAT with peanut husks (PH) and the preparation of composite materials.
2.6. Mechanical testing A mechanical tester (Lloyd Instruments, model LR5K, Bognor Regis, UK) was used to measure the tensile strength and the elongation at break according to ASTM D638. The test sample films, which were conditioned at 50 2% relative humidity for 24 h prior to the measurements, were prepared in a hydraulic press at 130 C, and then measurements were done at a crosshead speed of 20 mm/ min. Five measurements were performed for each sample, and the results were averaged to obtain a mean value. 2.7. Composite morphology A thin film (150 150 1 mm) of each composite was prepared with a hydraulic press and treated with vacuum oven at 60 C for 24 h. Specimens were cut according to ASTM D638. After rupture, a thin section of the fracture plane was removed. The thin sections were then coated with gold, and the fracture surface morphologies were observed using a scanning electron microscope (SEM, Hitachi, model S-1400, Tokyo, Japan). 2.8. Water absorption Samples were prepared for water absorption measurements by cutting into 60 25-mm strips (150 5 mm thickness) following ASTM D570. The samples were dried in a vacuum oven at 50 2 C for 8 h, cooled in a desiccator, and then immediately weighed to the nearest 0.001 g (this weight is designated Wc). Thereafter, the samples were immersed in distilled water and maintained at 30.0 0.1 C for a 120-day period. During this time, they were removed from the water at 3-day intervals, gently blotted with tissue paper to remove excess water from their surfaces, immediately weighed to the nearest 0.001 g (this weight is designated Ww), and returned to the water. Each Ww is an average value obtained from three measurements. The percentage of weight increase due to water absorption (Wf) was calculated to the nearest 0.01% according to Equation (1):
%Wf ¼
Ww Wc 100%: Wc
(1)
2.9. Microbiological sample preparation and exposure to A. aminovorans A. aminovorans (BCRC15819) was supplied by the Bioresource Collection and Research Center in Taiwan. The strain was cultivated at 26.0 0.1 C and stirred at 120 rpm in a medium consisting of
0.45 g of NB (nutrient broth), 0.75 g of peptone, and 150 mL of distilled water at pH 7.0 0.1. The culture was collected in its early stationary phase for cell entrapment. Samples were cast into films using a 45 15-mm plastic mold. Films were removed from the mold and rinsed several times with distilled water until the waste water had a neutral pH. The films were then clamped to a glass sheet and dried in a vacuum oven (50 2 C, 0.5 mm Hg, 24 h). After drying, the films were 0.05 0.02 mm thick. The dried films were placed in compost Petri dishes containing 30 mL of NB broth and A. aminovorans and incubated at pH 7.0 0.3, 26.0 0.1 C, and 50 5% relative humidity. After incubation, the films were washed extensively with deionized water and dried. Each study was conducted using three replicate test reactors and three replicate samples in each test reactor. Each result is therefore based on nine samples. 3. Results and discussion 3.1. FTIR/NMR analysis The FTIR spectra of unmodified PBAT and PBAT-g-MA are shown in Fig. 1A and B, respectively. The characteristic absorptions of PBAT [27] at 3300e3700, 1700e1760, and 500e1500 cm1 appeared in the spectra of both polymers, with two additional shoulders observed at 1785 and 1856 cm1 in the modified PBAT spectrum. These features are characteristic of anhydride carboxyl groups. Similar results have been reported previously [28]. The shoulders represent free acid in the modified polymer and therefore denote the grafting of MA onto PBAT. In the composite PBAT/PH (20 wt%), the peak assigned to the OH stretching vibration at 32003700 cm1 intensified (Fig. 1C) due to contributions from the eOH group of PH. The FTIR spectrum of the PBAT-g-MA/PH (20 wt%) composite in Fig. 1D revealed a peak at 1737 cm1 that was not present in the FTIR spectrum of the PBAT/ PH (20 wt%) blend. This peak was assigned to the ester carbonyl stretching vibration of the copolymer. Kim et al. [29] also reported an absorption peak at 1739 cm1 for this ester carbonyl group. These data suggest the formation of branched and cross-linked macromolecules in PBAT-g-MA/PH by covalent reaction of the anhydride carboxyl groups in PBAT-g-MA with the hydroxyl groups of PH. To further support this conclusion, solid-state 13C NMR spectra of PBAT and PBAT-g-MA were compared (Fig. 2A and B, respectively). The 13C NMR spectrum of neat PBAT (Fig. 2A) was similar to that measured by Shi et al. [30] and exhibited 10 peaks: (1) d ¼ 173.9 ppm; (2) d ¼ 34.6 ppm; (3), (5), (10) d ¼ 26.2 ppm; (4), (9) d ¼ 65.2 ppm; (6) d ¼ 164.9 ppm; (8) d ¼ 134.3 ppm; and (7) d ¼ 129.7 ppm. The 13C NMR spectrum of PBAT-g-MA showed
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Fig. 1. FTIR spectra of (A) PBAT, (B) PBAT-g-MA, (C) PBAT/PH (20 wt%), and (D) PBAT-gMA/PH (20 wt%).
additional peaks: (11) d ¼ 41.9 ppm; (12) d ¼ 37.8 ppm; and (13) eC]O d ¼ 170.8 ppm, thus confirming that MA was covalently grafted onto PBAT. The solid-state 13C NMR spectra of PBAT-g-MA/PH (20 wt%), PBAT/PH (20 wt%), and PH are shown in Fig. 2CeE. The PH spectrum in Fig. 2E is similar to that reported by Sobolev et al. [31]. Relative to unmodified PBAT, additional peaks were observed in the spectra of composites containing PBAT-g-MA. These additional peaks were located at d ¼ 41.9 ppm (11) and d ¼ 37.8 ppm (12). These same features were observed in previous studies [32] and indicate grafting of MA onto PBAT. However, the peak at d ¼ 170.8 ppm (C]O) (13) (shown in Fig. 2B), which is also typical for MA-grafted onto PBAT, was absent in the solid-state spectrum of PBAT-g-MA/PH (20 wt%). This is most likely a result of an additional condensation reaction between the anhydride carboxyl group of MA and the eOH group of PH that caused the peak at d ¼ 170.8 ppm to split into two bands (d ¼ 177.5 and 178.9 ppm). This additional reaction converted the fully acylated groups in the original PH to esters (represented by peaks 14 and 15 in Fig. 2C) and did not occur between PBAT and PH, as indicated by the absence of corresponding peaks in the FTIR spectrum of PBAT/PH (20 wt%) in Fig. 2D. The formation of ester groups significantly affects the mechanical properties of PBAT-g-MA/PH and is discussed in greater detail in the following sections. 3.2. X-Ray diffraction X-Ray diffractograms of pure PBAT, PBAT/PH (20 wt%), PBAT-gMA/PH (20 wt%), and PH are shown in Fig. 3AeD. Similar to the results of Fukushima et al. [33], pure PBAT (Fig. 3A) observed four diffraction peaks at about 17.6 , 20.5 , 22.9 , and 24.6 (related to basal reflections (010), (111), (100) and (111)), designated 1, 2, 3, and 4, respectively; and indicating a crystalline structure for PBAT. The diffractogram of neat PH in Fig. 3D also revealed two peaks at 15.1 and 22.7, designated 6 and 7, respectively. Peak as indicated by the existence of highly organized crystalline cellulose, and the secondary rather weak peak is a measure of a less organized
Fig. 2. Solid-state 13C NMR spectra of (A) PBAT, (B) PBAT-g-MA, (C) PBAT/PH (20 wt%), (D) PBAT-g-MA/PH (20 wt%), and (E) PH.
polysaccharide structure [34]. A comparison of the diffractograms of PBAT/PH and PH suggests that peaks 6 and 7 may be the result of physical dispersion of PH throughout the PBAT matrix. The PH is characteristic for the cellulose form and it does not change during compounding. Furthermore, Fig. 3C shows an additional peak at 18.1 (designated 5) in the diffractogram of the PBAT-g-MA/PH composite. This peak, also identified by Shogren et al. [35], may have been caused by the formation of ester carbonyl groups. This would indicate that the crystalline structure of the PBAT/PH composite was altered when PBAT-g-MA was used in place of PBAT. 3.3. Composite morphology In most composite materials, effective wetting and uniform dispersion of all components in a given matrix and strong interfacial adhesion between the phases are required to obtain a composite having satisfactory mechanical properties. In the current study, PH may be thought of as a dispersed phase within a PBAT or PBAT-g-MA matrix. To evaluate the composite morphology, SEM was employed to examine tensile fracture
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Fig. 3. X-ray diffraction patterns of (A) PBAT, (B) PBAT/PH, (C) PBAT-g-MA/PH, and (D) PH.
surfaces of PBAT/PH (20 wt%) and PBAT-g-MA/PH (20 wt%) samples. The SEM micrograph of PBAT/PH (20 wt%) in Fig. 4A shows that the PH in this composite tended to agglomerate into bundles and was unevenly distributed in the matrix. This poor dispersion was due to the formation of hydrogen bonds between PH fragments and the disparate hydrophilicities of PBAT and PH. Poor wetting in these composites was also noted (Fig. 4A) because of large difference in surface energy between the PH and the PBAT matrix. The PBAT-gMA/PH (20 wt%) micrograph in Fig. 4B shows a more homogeneous dispersion and better wetting of PH in the PBAT-g-MA matrix, indicated by the complete coverage of PBAT-g-MA on the fragments and the removal of both materials when a fragment was pulled from the bulk. This improved interfacial adhesion was due to the similar hydrophilicity of the two components, which allowed for the formation of branched and cross-linked macromolecules and prevented hydrogen bonding between PH fragments. 3.4. Mechanical properties Fig. 5 shows the variation in tensile strength and elongation at break with PH content for PBAT/PH and PBAT-g-MA/PH composites. The tensile strength and elongation at break of pure PBAT decreased after grafting with maleic anhydride. For PBAT/PH composites (Fig. 5A), the tensile strength at break decreased markedly and continuously with increasing PH content. This was attributed to poor dispersion of PH in the PBAT matrix, as previously discussed and as shown in Fig. 4A. The effect of this incompatibility on the mechanical properties of the composites was
Fig. 4. SEM micrographs showing the distribution and adhesion of PH in (A) PBAT/PH (20 wt%) and (B) PBAT-g-MA/PH (20 wt%) composites.
substantial. The PBAT-g-MA/PH composites in Fig. 5A exhibited unique behavior in regard to the tensile strength at break, which increased with increasing PH content despite the fact that PBAT-gMA had a lower tensile strength at break than pure PBAT. Furthermore, the tensile strength at break of the PBAT-g-MA/PH composites was constant with PH content beyond 20 wt%. This behavior was likely due to enhanced dispersion of PH in the PBATg-MA matrix resulting from the formation of branched or crosslinked macromolecules. Fig. 5B also indicates lower elongation at break values for the PBAT/PH composites relative to the PBAT-g-MA/PH composites. In PBAT/PH, the PH tended to agglomerate into bundles, illustrating the poor compatibility between the two phases. In the PBAT-g-MA/ PH composites, as shown in Fig. 5B, the elongation at break also decreased with increasing amounts of PH but exhibited greater elongation values than did PBAT/PH composites. However, these values were still lower than those of pure PBAT. The graphs in Fig. 5 indicate that the grafting reaction in PBAT-g-MA/PH composites improved the tensile strength and elongation at break of PBAT/PH. However, the degree of enhancement of the elongation at break was smaller than for the tensile strength at break. 3.5. Water absorption At the same PH content, the PBAT-g-MA/PH composites exhibited a higher resistance to water absorption than did the PBAT/PH composites (Fig. 6). The water resistance of the PBAT-gMA/PH composites was moderate, and it is proposed that the interaction of MA-grafted PBAT with PH increased the
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Fig. 6. Percent weight gain due to the absorption of water for PBAT/PH and PBAT-gMA/PH composites.
3.6. Biodegradation
Fig. 5. Effect of PH content on tensile strength (A) and elongation (B) at break is shown for PBAT/PH and PBAT-g-MA/PH composites.
hydrophobicity of PH in these composites. For both PBAT/PH and PBAT-g-MA/PH, the percentage water gain over the 120-day test period increased with higher PH content. Because the polymer chain arrangement in these systems is supposedly random, the above result was likely due to decreased chain mobility with greater amounts of PH and to the hydrophilic character of PH, which adheres weakly to the more hydrophobic PBAT.
Changes in the morphology of both PBAT and PBAT-g-MA/PH composites were noted as a function of the amount of time buried in an A. aminovorans compost. SEM micrographs taken after 30, 60, and 120 days in the A. aminovorans compost illustrate the extent of morphological change (Fig. 7). PBAT/PH (20 wt%) (Fig. 7FeH) exhibited larger and deeper pits that appeared to be more randomly distributed relative to those in the PBAT-g-MA/PH (20 wt%) composites (Fig. 7JeL). These analyses also indicate that biodegradation of the PH phase in PBAT/PH (20 wt%) increased with time, confirming the results presented in Fig. 8. After a 30-day incubation period, cell growth with gradual erosion and cracking was observed on the surface of the PBAT matrix (Fig. 7B). After 60 days, the disruption of the PBAT matrix structure became more obvious (Fig. 7C). This degradation was confirmed by increasing weight loss of the PBAT matrix with incubation time (Fig. 8), which reached nearly 15% after only 60 days. The most likely cause of this weight loss was biodegradation by A. aminovorans. Bacterial degradation of PBAT has been previously reported, and some have described degradation mechanisms involving enzymes such as lysozyme [36,37]. The results shown here indicate that A. aminovorans is very effective at degrading PBAT.
Fig. 7. SEM micrographs showing the morphology of PBAT (A through D), PBAT/PH (E through H), and PBAT-g-MA/PH (I through L) films as a function of incubation time in a Rhizopus oryzae compost.
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between mechanical properties and biodegradability of the composites should be considered. Acknowledgments The author thanks the National Science Council (Taipei City, Taiwan, R.O.C.) for financial support. References
Fig. 8. Weight loss percentages of PBAT, PBAT-g-MA, PBAT/PH, and PBAT-g-MA/PH as a function of incubation time in an Aminobacter aminovorans compost.
The SEM micrographs in Fig. 7 indicate that the PBAT-g-MA/PH (20 wt%) composites were more easily degraded than was pure PBAT. After a 30-day incubation period, the PBAT-g-MA/PH composite was coated with a biofilm of bacterial cells (Fig. 7J), indicating more cell growth than on PBAT at the same incubation time. Moreover, at 60 and 120 days, larger pores were apparent on the PBAT-g-MA/PH composite (Fig. 7K and L), indicating a higher level of degradation. The degree of weight loss of the PBAT-g-MA/ PH composites was also accelerated relative to that of PBAT, exceeding 30% after 120 days (Fig. 8). These results clearly demonstrate that the addition of PH to the MA-grafted PBAT enhanced the biodegradability of the composite. Fig. 8 shows the percentage weight change as a function of time for PBAT/PH and PBAT-g-MA/PH composites buried in A. aminovorans compost. For both composites, the degree of weight loss increased with PH content. Composites with 40 wt% PH degraded rapidly over the first 120 days, losing a mass equivalent to their approximate PH content, and showed a gradual decrease in weight over the next 60 days. PBAT/PH exhibited a weight loss of approximately 3e10 wt% more than PBAT-g-MA/PH. 4. Conclusions The compatibility and mechanical properties of PH blended with PBAT and maleic anhydride-modified PBAT (PBAT-g-MA) were examined. FTIR and NMR analyses revealed the formation of ester groups due to reactions between eOH groups in PH and anhydride carboxyl groups in PBAT-g-MA, significantly altering the structure of the composite material. The morphology of PBAT-g-MA/PH composites was consistent with good adhesion between the PH phase and the PBAT-g-MA matrix. In mechanical tests, PBAT-g-MA enhanced the mechanical properties of the composite, especially the tensile strength. Although the water resistance of PBAT-g-MA/ PH was higher than that of PBAT/PH, the biodegradation rate of PBAT-g-MA/PH was lower than that of PBAT/PH but higher than that of pure PBAT when incubated with A. aminovorans. After 120 days, the PBAT-g-MA/PH (40 wt%) composite suffered weight loss of greater than 80%. The degree of biodegradation increased with increasing PH content. Finally, there was a conflict between mechanical properties and biodegradability of the composites. For commercial applications of the proposed composites, the balance
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Polymer Degradation and Stability journal homepage: www.elsevier.com/locate/polydegstab
Utilization of peanut husks as a filler in aliphaticearomatic polyesters: Preparation, characterization, and biodegradability Chin-San Wu* Department of Chemical and Biochemical Engineering, Kao Yuan University, Kaohsiung County 82101, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history: Received 20 May 2012 Received in revised form 12 July 2012 Accepted 21 July 2012 Available online 11 August 2012
The biodegradability, morphology, and mechanical properties of composite materials made of poly(butylene adipate-co-terephthalate) (PBAT) and peanut husks (PH) were evaluated. Composites containing maleic anhydride-grafted PBAT (PBAT-g-MA/PH) exhibited noticeably superior mechanical properties because of greater compatibility between the two components. The dispersion of PH in the PBAT-g-MA matrix was highly homogeneous as a result of ester formation between the anhydride carboxyl groups of PBAT-g-MA and hydroxyl groups in PH and the consequent creation of branched and cross-linked macromolecules. Each composite was subjected to biodegradation tests in Aminobacter aminovorans compost. Morphological observations indicated severe disruption of film structure after 60 days of incubation, and both the PBAT and the PBAT-g-MA/PH composite films were eventually completely degraded. Water resistance of PBAT-g-MA/PH was higher than that of PBAT/PH, although the weight loss of composites buried in A. aminovorans compost indicated that both were biodegradable, even at high levels of PH substitution. The PBAT-g-MA/PH films were more biodegradable than those made of PBAT, implying a strong connection between these characteristics and biodegradability. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Biodegradable Polyesters Peanut husks Composites
1. Introduction It is becoming increasingly difficult to find disposal sites for plastic-based materials [1e3]. The development of renewable and green biodegradable materials has been a trend in environmental projects in recent years. Green composites are gradually replacing general plastics to achieve the goal of environmental sustainability [4e6]. In recent years, because of economic and environmental concerns such as waste management and carbon emissions, the use of biodegradable polyesters from renewable or fossil sources, or a combination of both, has gained research and industry attention [7,8]. The biodegradation of poly(butylene adipate-coterephthalate) (PBAT) and the resulting aliphatic-co-aromatic copolyester has been investigated [9,10]. To obtain biodegradable polymers having satisfactory mechanical properties, many researchers have begun to synthesize aliphatic-co-aromatic copolyesters [11,12]. PBAT biodegrades into naturally-occurring products within only a few years, in contrast to conventional plastics like polystyrene (PS) and polypropylene (PP) that require hundreds or even thousands of years to biodegrade. The degradation of PBAT may result
* Fax: þ886 7 6077788. E-mail address: [email protected]. 0141-3910/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.polymdegradstab.2012.07.027
from chain scission and the generation of free radicals in the aromatic structures [13,14]. Because of its excellent biocompatibility and physical properties, PBAT and its copolymers have been proposed for use in various biomaterial applications, and several commercially successful applications have emerged [15,16]. PBAT begins to degrade after only a few days in soil and enzymatic environments [17,18]. Unfortunately, widespread commercialization of PBAT has been limited because its production is both complex and expensive. However, these limitations can potentially be overcome by using PBAT composites. The composites combine PBAT with polymers and natural compounds found in biodegradable agricultural residues such as rice husks, rice straw, and peanut husks (PH). These residues are abundant, inexpensive, renewable, and fully biodegradable [19,20]. Xiao et al. [21] explored the use of underutilized byproducts from both agricultural and industrial production to reduce environmental pollution. Composites of PBAT and agricultural residues would likely be less expensive than pure PBAT, and their biodegradability and mechanical properties can be adjusted by varying the composition [22]. There is also growing interest in exploiting renewable resources as raw materials for the production of commercially-useful biodegradable plastics [23]. Several researchers have successfully developed composites of thermoplastic polymers with lignin derived from pecan shell and peanut hull flour [24]. PH is an abundant agricultural resource. Although cellulose fibers in plastic
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composites can yield many desirable properties, fiber dispersion and fiber-matrix compatibility remains problematic [25]. Additionally, although composites with high fiber contents are inexpensive, their high viscosities and other undesirable rheological properties during processing have limited the application of these materials. This report describes a systematic investigation of the mechanical properties and biodegradability of PH composites made with PBAT and maleic anhydride-grafted-grafted PBAT (PBATg-MA). The composites were characterized using Fourier transform infrared spectroscopy (FTIR), 13C nuclear magnetic resonance (NMR) spectroscopy, and X-ray diffraction (XRD) to identify bulk structural changes induced by the maleic anhydride moiety. Water absorption and weight loss of blends exposed to Aminobacter aminovorans compost were also measured as indicators of water resistance and biodegradability.
Recovered PH samples obtained prior to grinding consisted of a mixture of fine pale-yellow fragments up to 0.5e3 cm long. For utilizing, the fragments were processed as follows: Firstly, crude PH was dried at 50e60 C under vacuum for 2 days. Then the product was ground in a high-speed rotary grinder (Yowlin Industrial Co. Ltd., Taiwan) at 90 s for six times and was vacuum-dried at 50e60 C for 2 days again. Thereafter, the crushed PH was passed through 200-mesh sieve to have PH powder at about 10e40 mm and was purified by immersing 60 g of PH powder in 1000 mL of distilled water for 2 days to remove any water-soluble components. Eventually, the PH samples were further air-dried for 2 days at 50e60 C and vacuum-dried at 105 C for at least 6 h to have the moisture content fall to 5.0 0.2%. The entire processing procedures can also be seen in Scheme 2.
2. Experimental
2.4. Composite preparation
2.1. Materials
Prior to composite fabrication, PH samples were washed with acetone and dried in an oven at 105 C for 24 h. Composites were prepared in a “Plastograph” 200-Nm Mixer W50EHT with a blade rotor (Brabender, Dayton, USA). The composites were mixed between 120 and 130 C for 20 min at a rotor speed of 50 rpm. Samples were prepared with mass ratios of PH to PBAT or to PBATg-MA of 10/90, 20/80, 30/70, and 40/60. Residual MA in the PBAT-gMA reaction mixture was removed via acetone extraction prior to the preparation of PBAT-g-MA/PH. After mixing, the composites were pressed into thin plates with a hot press and placed in a dryer for cooling. These thin plates were cut to standard sample dimensions for further characterization.
PBAT resins were purchased from BASF Corporation (Florham Park, USA). Maleic anhydride (MA), obtained from Sigma (St. Louis, USA), was purified before use by recrystallization from chloroform. Benzoyl peroxide (BPO; Sigma) was used as an initiator and was purified by dissolution in chloroform and reprecipitation in methanol. A PH composed of 70e79% cellulose and 10.1% hemicelluloses was obtained from the Council of Agriculture Executive Yuan (Taiwan). The levels of protein, lipid and ash in the PH were negligible.
2.3. Peanut husk (PH) processing
2.2. PBAT-g-MA copolymer 2.5. NMR/FTIR/XRD analyses The grafting reaction of MA onto PBAT is illustrated in Scheme 1. In preliminary experiments using tetrahydrofuran as the solvent, different amounts of BPO and MA were used in the grafting reaction at 45 2 C and 60 rpm for 10 h. The grafted product (4 g) was dissolved in 200 mL of refluxing tetrahydrofuran at 45 2 C, and the hot solution was filtered through several layers of cheesecloth. The cheesecloth was washed with 600 mL of acetone to remove the tetrahydrofuran-insoluble, unreacted maleic anhydride, and the remaining product was dried in a vacuum oven at 80 C for 24 h. The tetrahydrofuran-soluble component of the filtrate was extracted five times using 600 mL of cold acetone for each extraction. A grafting percentage of approximately 1.06 wt% was determined by titration [26]. BPO and MA loadings were maintained at 0.3 and 10 wt%, respectively.
Solid-state 13C NMR was performed with an AMX-400 NMR spectrometer, and spectra were obtained at 100 MHz under crosspolarization while spinning at the magic angle. Power decoupling conditions were set with a 90 pulse and a 4-s cycle time. Fourier transform infrared spectrometry (FTIR; FTS-7PC type; Bio-Rad, Hercules) was used to investigate the grafting reaction of MA onto PBAT and to verify ester bond formation between the anhydride carboxyl groups in PBAT-g-MA with the hydroxyl groups of PH. Samples subjected to FTIR analysis were ground into fine powders in a milling machine and pressed into pellets with potassium bromide. XRD diffractograms were recorded using a D/ max 3-V X-ray diffractometer (Rigaku, Tokyo, Japan) with a Cu target and Ka radiation at a scanning rate of 2 /min.
Scheme 1. Grafting reaction of MA onto PBAT.
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Scheme 2. Modification of PBAT with peanut husks (PH) and the preparation of composite materials.
2.6. Mechanical testing A mechanical tester (Lloyd Instruments, model LR5K, Bognor Regis, UK) was used to measure the tensile strength and the elongation at break according to ASTM D638. The test sample films, which were conditioned at 50 2% relative humidity for 24 h prior to the measurements, were prepared in a hydraulic press at 130 C, and then measurements were done at a crosshead speed of 20 mm/ min. Five measurements were performed for each sample, and the results were averaged to obtain a mean value. 2.7. Composite morphology A thin film (150 150 1 mm) of each composite was prepared with a hydraulic press and treated with vacuum oven at 60 C for 24 h. Specimens were cut according to ASTM D638. After rupture, a thin section of the fracture plane was removed. The thin sections were then coated with gold, and the fracture surface morphologies were observed using a scanning electron microscope (SEM, Hitachi, model S-1400, Tokyo, Japan). 2.8. Water absorption Samples were prepared for water absorption measurements by cutting into 60 25-mm strips (150 5 mm thickness) following ASTM D570. The samples were dried in a vacuum oven at 50 2 C for 8 h, cooled in a desiccator, and then immediately weighed to the nearest 0.001 g (this weight is designated Wc). Thereafter, the samples were immersed in distilled water and maintained at 30.0 0.1 C for a 120-day period. During this time, they were removed from the water at 3-day intervals, gently blotted with tissue paper to remove excess water from their surfaces, immediately weighed to the nearest 0.001 g (this weight is designated Ww), and returned to the water. Each Ww is an average value obtained from three measurements. The percentage of weight increase due to water absorption (Wf) was calculated to the nearest 0.01% according to Equation (1):
%Wf ¼
Ww Wc 100%: Wc
(1)
2.9. Microbiological sample preparation and exposure to A. aminovorans A. aminovorans (BCRC15819) was supplied by the Bioresource Collection and Research Center in Taiwan. The strain was cultivated at 26.0 0.1 C and stirred at 120 rpm in a medium consisting of
0.45 g of NB (nutrient broth), 0.75 g of peptone, and 150 mL of distilled water at pH 7.0 0.1. The culture was collected in its early stationary phase for cell entrapment. Samples were cast into films using a 45 15-mm plastic mold. Films were removed from the mold and rinsed several times with distilled water until the waste water had a neutral pH. The films were then clamped to a glass sheet and dried in a vacuum oven (50 2 C, 0.5 mm Hg, 24 h). After drying, the films were 0.05 0.02 mm thick. The dried films were placed in compost Petri dishes containing 30 mL of NB broth and A. aminovorans and incubated at pH 7.0 0.3, 26.0 0.1 C, and 50 5% relative humidity. After incubation, the films were washed extensively with deionized water and dried. Each study was conducted using three replicate test reactors and three replicate samples in each test reactor. Each result is therefore based on nine samples. 3. Results and discussion 3.1. FTIR/NMR analysis The FTIR spectra of unmodified PBAT and PBAT-g-MA are shown in Fig. 1A and B, respectively. The characteristic absorptions of PBAT [27] at 3300e3700, 1700e1760, and 500e1500 cm1 appeared in the spectra of both polymers, with two additional shoulders observed at 1785 and 1856 cm1 in the modified PBAT spectrum. These features are characteristic of anhydride carboxyl groups. Similar results have been reported previously [28]. The shoulders represent free acid in the modified polymer and therefore denote the grafting of MA onto PBAT. In the composite PBAT/PH (20 wt%), the peak assigned to the OH stretching vibration at 32003700 cm1 intensified (Fig. 1C) due to contributions from the eOH group of PH. The FTIR spectrum of the PBAT-g-MA/PH (20 wt%) composite in Fig. 1D revealed a peak at 1737 cm1 that was not present in the FTIR spectrum of the PBAT/ PH (20 wt%) blend. This peak was assigned to the ester carbonyl stretching vibration of the copolymer. Kim et al. [29] also reported an absorption peak at 1739 cm1 for this ester carbonyl group. These data suggest the formation of branched and cross-linked macromolecules in PBAT-g-MA/PH by covalent reaction of the anhydride carboxyl groups in PBAT-g-MA with the hydroxyl groups of PH. To further support this conclusion, solid-state 13C NMR spectra of PBAT and PBAT-g-MA were compared (Fig. 2A and B, respectively). The 13C NMR spectrum of neat PBAT (Fig. 2A) was similar to that measured by Shi et al. [30] and exhibited 10 peaks: (1) d ¼ 173.9 ppm; (2) d ¼ 34.6 ppm; (3), (5), (10) d ¼ 26.2 ppm; (4), (9) d ¼ 65.2 ppm; (6) d ¼ 164.9 ppm; (8) d ¼ 134.3 ppm; and (7) d ¼ 129.7 ppm. The 13C NMR spectrum of PBAT-g-MA showed
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Fig. 1. FTIR spectra of (A) PBAT, (B) PBAT-g-MA, (C) PBAT/PH (20 wt%), and (D) PBAT-gMA/PH (20 wt%).
additional peaks: (11) d ¼ 41.9 ppm; (12) d ¼ 37.8 ppm; and (13) eC]O d ¼ 170.8 ppm, thus confirming that MA was covalently grafted onto PBAT. The solid-state 13C NMR spectra of PBAT-g-MA/PH (20 wt%), PBAT/PH (20 wt%), and PH are shown in Fig. 2CeE. The PH spectrum in Fig. 2E is similar to that reported by Sobolev et al. [31]. Relative to unmodified PBAT, additional peaks were observed in the spectra of composites containing PBAT-g-MA. These additional peaks were located at d ¼ 41.9 ppm (11) and d ¼ 37.8 ppm (12). These same features were observed in previous studies [32] and indicate grafting of MA onto PBAT. However, the peak at d ¼ 170.8 ppm (C]O) (13) (shown in Fig. 2B), which is also typical for MA-grafted onto PBAT, was absent in the solid-state spectrum of PBAT-g-MA/PH (20 wt%). This is most likely a result of an additional condensation reaction between the anhydride carboxyl group of MA and the eOH group of PH that caused the peak at d ¼ 170.8 ppm to split into two bands (d ¼ 177.5 and 178.9 ppm). This additional reaction converted the fully acylated groups in the original PH to esters (represented by peaks 14 and 15 in Fig. 2C) and did not occur between PBAT and PH, as indicated by the absence of corresponding peaks in the FTIR spectrum of PBAT/PH (20 wt%) in Fig. 2D. The formation of ester groups significantly affects the mechanical properties of PBAT-g-MA/PH and is discussed in greater detail in the following sections. 3.2. X-Ray diffraction X-Ray diffractograms of pure PBAT, PBAT/PH (20 wt%), PBAT-gMA/PH (20 wt%), and PH are shown in Fig. 3AeD. Similar to the results of Fukushima et al. [33], pure PBAT (Fig. 3A) observed four diffraction peaks at about 17.6 , 20.5 , 22.9 , and 24.6 (related to basal reflections (010), (111), (100) and (111)), designated 1, 2, 3, and 4, respectively; and indicating a crystalline structure for PBAT. The diffractogram of neat PH in Fig. 3D also revealed two peaks at 15.1 and 22.7, designated 6 and 7, respectively. Peak as indicated by the existence of highly organized crystalline cellulose, and the secondary rather weak peak is a measure of a less organized
Fig. 2. Solid-state 13C NMR spectra of (A) PBAT, (B) PBAT-g-MA, (C) PBAT/PH (20 wt%), (D) PBAT-g-MA/PH (20 wt%), and (E) PH.
polysaccharide structure [34]. A comparison of the diffractograms of PBAT/PH and PH suggests that peaks 6 and 7 may be the result of physical dispersion of PH throughout the PBAT matrix. The PH is characteristic for the cellulose form and it does not change during compounding. Furthermore, Fig. 3C shows an additional peak at 18.1 (designated 5) in the diffractogram of the PBAT-g-MA/PH composite. This peak, also identified by Shogren et al. [35], may have been caused by the formation of ester carbonyl groups. This would indicate that the crystalline structure of the PBAT/PH composite was altered when PBAT-g-MA was used in place of PBAT. 3.3. Composite morphology In most composite materials, effective wetting and uniform dispersion of all components in a given matrix and strong interfacial adhesion between the phases are required to obtain a composite having satisfactory mechanical properties. In the current study, PH may be thought of as a dispersed phase within a PBAT or PBAT-g-MA matrix. To evaluate the composite morphology, SEM was employed to examine tensile fracture
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Fig. 3. X-ray diffraction patterns of (A) PBAT, (B) PBAT/PH, (C) PBAT-g-MA/PH, and (D) PH.
surfaces of PBAT/PH (20 wt%) and PBAT-g-MA/PH (20 wt%) samples. The SEM micrograph of PBAT/PH (20 wt%) in Fig. 4A shows that the PH in this composite tended to agglomerate into bundles and was unevenly distributed in the matrix. This poor dispersion was due to the formation of hydrogen bonds between PH fragments and the disparate hydrophilicities of PBAT and PH. Poor wetting in these composites was also noted (Fig. 4A) because of large difference in surface energy between the PH and the PBAT matrix. The PBAT-gMA/PH (20 wt%) micrograph in Fig. 4B shows a more homogeneous dispersion and better wetting of PH in the PBAT-g-MA matrix, indicated by the complete coverage of PBAT-g-MA on the fragments and the removal of both materials when a fragment was pulled from the bulk. This improved interfacial adhesion was due to the similar hydrophilicity of the two components, which allowed for the formation of branched and cross-linked macromolecules and prevented hydrogen bonding between PH fragments. 3.4. Mechanical properties Fig. 5 shows the variation in tensile strength and elongation at break with PH content for PBAT/PH and PBAT-g-MA/PH composites. The tensile strength and elongation at break of pure PBAT decreased after grafting with maleic anhydride. For PBAT/PH composites (Fig. 5A), the tensile strength at break decreased markedly and continuously with increasing PH content. This was attributed to poor dispersion of PH in the PBAT matrix, as previously discussed and as shown in Fig. 4A. The effect of this incompatibility on the mechanical properties of the composites was
Fig. 4. SEM micrographs showing the distribution and adhesion of PH in (A) PBAT/PH (20 wt%) and (B) PBAT-g-MA/PH (20 wt%) composites.
substantial. The PBAT-g-MA/PH composites in Fig. 5A exhibited unique behavior in regard to the tensile strength at break, which increased with increasing PH content despite the fact that PBAT-gMA had a lower tensile strength at break than pure PBAT. Furthermore, the tensile strength at break of the PBAT-g-MA/PH composites was constant with PH content beyond 20 wt%. This behavior was likely due to enhanced dispersion of PH in the PBATg-MA matrix resulting from the formation of branched or crosslinked macromolecules. Fig. 5B also indicates lower elongation at break values for the PBAT/PH composites relative to the PBAT-g-MA/PH composites. In PBAT/PH, the PH tended to agglomerate into bundles, illustrating the poor compatibility between the two phases. In the PBAT-g-MA/ PH composites, as shown in Fig. 5B, the elongation at break also decreased with increasing amounts of PH but exhibited greater elongation values than did PBAT/PH composites. However, these values were still lower than those of pure PBAT. The graphs in Fig. 5 indicate that the grafting reaction in PBAT-g-MA/PH composites improved the tensile strength and elongation at break of PBAT/PH. However, the degree of enhancement of the elongation at break was smaller than for the tensile strength at break. 3.5. Water absorption At the same PH content, the PBAT-g-MA/PH composites exhibited a higher resistance to water absorption than did the PBAT/PH composites (Fig. 6). The water resistance of the PBAT-gMA/PH composites was moderate, and it is proposed that the interaction of MA-grafted PBAT with PH increased the
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Fig. 6. Percent weight gain due to the absorption of water for PBAT/PH and PBAT-gMA/PH composites.
3.6. Biodegradation
Fig. 5. Effect of PH content on tensile strength (A) and elongation (B) at break is shown for PBAT/PH and PBAT-g-MA/PH composites.
hydrophobicity of PH in these composites. For both PBAT/PH and PBAT-g-MA/PH, the percentage water gain over the 120-day test period increased with higher PH content. Because the polymer chain arrangement in these systems is supposedly random, the above result was likely due to decreased chain mobility with greater amounts of PH and to the hydrophilic character of PH, which adheres weakly to the more hydrophobic PBAT.
Changes in the morphology of both PBAT and PBAT-g-MA/PH composites were noted as a function of the amount of time buried in an A. aminovorans compost. SEM micrographs taken after 30, 60, and 120 days in the A. aminovorans compost illustrate the extent of morphological change (Fig. 7). PBAT/PH (20 wt%) (Fig. 7FeH) exhibited larger and deeper pits that appeared to be more randomly distributed relative to those in the PBAT-g-MA/PH (20 wt%) composites (Fig. 7JeL). These analyses also indicate that biodegradation of the PH phase in PBAT/PH (20 wt%) increased with time, confirming the results presented in Fig. 8. After a 30-day incubation period, cell growth with gradual erosion and cracking was observed on the surface of the PBAT matrix (Fig. 7B). After 60 days, the disruption of the PBAT matrix structure became more obvious (Fig. 7C). This degradation was confirmed by increasing weight loss of the PBAT matrix with incubation time (Fig. 8), which reached nearly 15% after only 60 days. The most likely cause of this weight loss was biodegradation by A. aminovorans. Bacterial degradation of PBAT has been previously reported, and some have described degradation mechanisms involving enzymes such as lysozyme [36,37]. The results shown here indicate that A. aminovorans is very effective at degrading PBAT.
Fig. 7. SEM micrographs showing the morphology of PBAT (A through D), PBAT/PH (E through H), and PBAT-g-MA/PH (I through L) films as a function of incubation time in a Rhizopus oryzae compost.
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between mechanical properties and biodegradability of the composites should be considered. Acknowledgments The author thanks the National Science Council (Taipei City, Taiwan, R.O.C.) for financial support. References
Fig. 8. Weight loss percentages of PBAT, PBAT-g-MA, PBAT/PH, and PBAT-g-MA/PH as a function of incubation time in an Aminobacter aminovorans compost.
The SEM micrographs in Fig. 7 indicate that the PBAT-g-MA/PH (20 wt%) composites were more easily degraded than was pure PBAT. After a 30-day incubation period, the PBAT-g-MA/PH composite was coated with a biofilm of bacterial cells (Fig. 7J), indicating more cell growth than on PBAT at the same incubation time. Moreover, at 60 and 120 days, larger pores were apparent on the PBAT-g-MA/PH composite (Fig. 7K and L), indicating a higher level of degradation. The degree of weight loss of the PBAT-g-MA/ PH composites was also accelerated relative to that of PBAT, exceeding 30% after 120 days (Fig. 8). These results clearly demonstrate that the addition of PH to the MA-grafted PBAT enhanced the biodegradability of the composite. Fig. 8 shows the percentage weight change as a function of time for PBAT/PH and PBAT-g-MA/PH composites buried in A. aminovorans compost. For both composites, the degree of weight loss increased with PH content. Composites with 40 wt% PH degraded rapidly over the first 120 days, losing a mass equivalent to their approximate PH content, and showed a gradual decrease in weight over the next 60 days. PBAT/PH exhibited a weight loss of approximately 3e10 wt% more than PBAT-g-MA/PH. 4. Conclusions The compatibility and mechanical properties of PH blended with PBAT and maleic anhydride-modified PBAT (PBAT-g-MA) were examined. FTIR and NMR analyses revealed the formation of ester groups due to reactions between eOH groups in PH and anhydride carboxyl groups in PBAT-g-MA, significantly altering the structure of the composite material. The morphology of PBAT-g-MA/PH composites was consistent with good adhesion between the PH phase and the PBAT-g-MA matrix. In mechanical tests, PBAT-g-MA enhanced the mechanical properties of the composite, especially the tensile strength. Although the water resistance of PBAT-g-MA/ PH was higher than that of PBAT/PH, the biodegradation rate of PBAT-g-MA/PH was lower than that of PBAT/PH but higher than that of pure PBAT when incubated with A. aminovorans. After 120 days, the PBAT-g-MA/PH (40 wt%) composite suffered weight loss of greater than 80%. The degree of biodegradation increased with increasing PH content. Finally, there was a conflict between mechanical properties and biodegradability of the composites. For commercial applications of the proposed composites, the balance
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