Enhancement and Investigation of Biodegradability of Poly(Methyl Methacrylate) and Poly(vinyl chloride) by Blending with Cellulose Derivatives


 Presently, society needs a more eco-friendly alternative for non-biodegradable polymers, nonetheless, the synthetic polymers have established the market because of cost and easy to manufacture. To address the challenge of reducing the lifetime of degradation of these polymers the scope of blending natural biopolymers is effective. This paper focuses on confirming the effectiveness of biodegradation in the molecular level of polymer blends between synthetic polymers and biopolymers. The synthetic polymers such as poly(methyl methacrylate) (PMMA) and poly(vinyl chloride) (PVC) were blended with varying compositions of biodegradable cellulose acetate butyrate (CAB). Using dimethylformamide (DMF) the films of PMMA/CAB, PVC/CAB blends were prepared by the solution casting method. Four different methods for studying biodegradability of these blends namely, soil burial test, enzymatic degradation, activated sludge degradation followed by microbial degradation was performed. The confirmation of degradation was done by NMR, FTIR and Gel Permeation Chromatography (GPC) studies. Moreover, degradation analyses were determined by weight loss method. Sufficient biodegradability was shown with an increase in CAB content in the blend. This work provides an approach for bringing about the degradation of synthetic polymers without much compromise on their properties. Also the type of microorganisms that effectively degrades these polymer bends can be known.


Introduction
Common polymers like polypropylene, PMMA, PVC, polyethylene are extensively used and reusing or recycling them is a serious task. Even their composites add-on to the non-biodegradable wastes throughout the world. The alternative is the use of biodegradable polymers which mainly originates from renewable sources. However, their properties of brittleness, low thermal stability, water vapor permeability and uncontrolled molecular weight are main challenges that are yet to overcome when compared to synthetic polymers. Moreover, there are no single biodegradable polymers which can be used as such in applications such as carry bags, biomedical, food package, etc., Therefore, it is desirable to modify existing synthetic polymers by blending with a wide range of biopolymers, llers and bring about enhanced degradation [1]. Some researchers have attempted for preparing these kinds of composite polymers by including biopolymers into synthetic polymers [2][3][4]. Optimum balancing of physical and biodegradation properties of biopolymer/synthetic polymer blends will minimize the waste disposal problems. Biopolymer nanocomposites have a scope in industrial sectors as it is easy to process and have slightly greater biodegradation property [1]. Cellulose is a biopolymer that is found in abundance in wood and bacterial origin. As untreated cellulose behaves as thermosetting polymer and has less solubility. On the other hand cellulose derivatives are thermoplastics in nature and easy to process which makes it blend with synthetic polymers. Cellulose derivatives are readily biodegradable by microorganisms that utilize cellulose enzymes, but due to the additional acetyl groups cellulose requires the presence of esterases. Thereby the blending of the CAB will induce biodegradation in the synthetic polymer. PMMA a versatile synthetic polymer has enormous useful properties required in industrial and pharmaceutical applications. The literature survey on PMMA/Cellulose shows that the higher concentration of cellulose improves the bonding within them. PMMA/Cellulose blends [5] were subjected to dynamic mechanical analysis showed greater interaction at a high concentration of cellulose with PMMA. The nanocomposites with PMMA molecules covalently grafted to cellulose exhibited much higher optical transparency, thermal stability, and hygro-mechanical properties than the control samples [6]. PMMA/2,2,6,6-tetramethylpiperidyl-1-oxyl oxidized CNFs (PMMA/TOCN) nanocomposites with high transparency, controllable birefringence and enhanced mechanical properties exhibit great potential for the applications in the optical devices and engineering eld [7]. Porosity and stability can be seen in membranes based on CA/PMMA which was used for separation of proteins and toxic heavy metals [8].
To effectively modify the synthetic polymer, few grafted copolymers based on cellulose-g-PMMA found to be more moisture resistant and also exhibited better chemical and thermal resistance [9]. Carboxymethyl cellulose-g-PMMA showed thermal stability better than that of PMMA [10]. Nevertheless, none of the literature discussed the biodegradation of these bers/ lms. Hence, this paper focuses on the aspects of PMMA/CAB degradation. One more synthetic polymer PVC which is dominated in pipe and automobile industries is of major concern as this polymer is non-degradable. The preparation of PVC and biopolymer composites is challenging and requires more study. Cellulose Acetate (CA) and PVC nano ber mats were electrospun into nano bers which showed smooth bers at 14% CA and solution concentration had a signi cant in uence on the tensile strength of the nano ber mats [11]. It was found that there are no biodegradable studies on PVC/cellulose derivative lms. CAB as one of the biodegradable and biocompatible cellulose materials has attracted much attention in both academic and industrial elds ranging from a food package, biomedical products, clothing to automotive materials [12]. Hence, this paper reports for the rst time the preparation and degradation of PVC/CAB lm in various standard conditions. Different ratios of lms PMMA/CAB, PVC/CAB blends were prepared and characterized chemical, spectroscopic, and chromatographic techniques. A comparison of the mode of degradation was made to understand the microbial degradation as well as the physical degradation of the polymer. This paper has been split into two parts, (i) The rst part deals using soil-burial, activated sludge, buffer weight loss of polymer blend lm monitored, and also using soil-burial method mechanical strength of lms are monitored for two months [13,14]. (ii) The second part deals with the degradation of polymer to smaller elements was monitored by microbial degradation method and veri ed using FTIR, NMR, GPC techniques [15,16].

Materials And Methods
PMMA, PVC, and CAB were obtained from commercial sources. The viscosity average molecular weight of PMMA, PVC, and CAB were 75000, 101000, 70000 g mol − 1 , respectively. Bushnell-Hass broth and Bushnell-Hass agar (BH, Hi-Media) were used as the medium. All other chemicals used were of analytical reagent grade. Dimethylformamide (DMF) was used as a common solvent for preparing polymer solutions of CAB and PMMA and the preparation of PVC-CAB polyblends. We have previously prepared synthetic/natural polymer blend and studied their biodegradability the procedure is the same as Krishna et al. [14]. Brie y, 1g of polymers was dissolved in 50 mL of DMF and at ambient temperature. Composites were prepared by mixing different ratios of blends. The solutions were stirred well for an hour and solution cast on the petri dish. Films of 0.2-0.4 mm were obtained.
Soil Burial Degradation study [17,18] As reported in the literature about the soil nature [14] the blend lms were subjected to soil burial tests by maintaining 25% moisture weight. The lms were taken out, washed with water, dried and weighed again accurately to know the degradation in the intervals of 5, 10 and 15 days. In the case of soil adhering to the blend lms, the lms were washed and extracted with DMF. Using ltration, the soil was separated after evaporating the solvent residue. The experiment was repeated thrice and results were reproducible with ± 2% error.

Activated Sludge Degradation study
Activated sludge was kindly provided by BASF Company. The characteristics of the sludge have been reported in [14]. Aeration was provided for jars containing xed volumes of activated sludge and blend lms. The degraded lms were tested after 5, 10, 15 days after washing with distilled water and drying at 60°C. The experiment was repeated thrice and results were within ± 3% error.

Enzymatic Degradation study
The lms were tested as reported in [14] using enzyme lipase from the porcine pancreas in buffer solution. The test was reproduced thrice with ± 3% error.

Sample preparation and bacteria used
Bushnell-Hass agar (BH, Hi-Media) and Bushnell-Hass broth were used for detecting the biodegradation process. The pH of the medium was set to 7. The mixture of bacteria culture by pseudomonas, E-coli, Bacillus, and Klebsiella was used in this study. Commercially available enzyme Lipase was obtained from Hi-Media. As the sole carbon source about 10 mL of CAB, PMMA/CAB (30:70), PMMA/CAB (50:50), PVC/CAB (30:70), PVC/CAB (30:70) solutions with control was taken in Erlenmeyer asks and dissolved in dichloromethane. 50 ppm of mixed culture (pseudomonas, E-coli, Bacillus, Klebsiella) was inoculated. The test was carried as reported in [14]. After 30 days of the incubation period, the residual blend lms were extracted with an equal volume of dichloromethane (DCM). The resultant solute of polymer blends (1 µL) after evaporating the solvent was analyzed by using FTIR, NMR and Gel Permeation Chromatography (GPC). Tetrahydrofuran (THF) was used as eluent with a ow rate of 1 ml min − 1 at 60°C.

Result And Discussions
CAB was found to be miscible in both PVC and PMMA solutions [14] indicating CAB chains have speci c interaction with PVC and PMMA.

Soil burial degradation
Soil degradation test of PMMA/CAB blend lms showed 0.3 to 2.95% of degradation order, while the PVC/CAB blend lms reduced to 2.4%. The blend with more CAB showed high degradation as seen in Fig. 1a and 1b. The polymers exposed to soil might have initially experienced biodegradation, where microorganisms consume the natural cellulose component. Consequently, the oxygen can attack the newly generated surface with the formation of peroxides, hydroperoxides, oxides etc., which promote the scission of polymeric chains into small fragments. These chains are more susceptible to microorganism attack [17,18]. Soil bacteria and fungi might be responsible for degradation [19].

Enzymatic degradation
In the presence of phosphate buffer the blends are initially hydrolyzed and then followed by enzymatic degradation. Lipase from porcine pancreas under controlled environment was able to degrade about 0.9-4.95% for PMMA/CAB blend and 0.6-4.42% for PVC/CAB blends ( Fig. 1c and 1d). Within fteen days the blends showed biodegradation to an extent pure CAB. Therefore, enzymes have a major contribution to the biodegradation of the blends.

Degradation in activated sludge
The blends subjected to activated sludge for 15 days showed degradation of about 1.1 to 5.21 % for PMMA/CAB blends and 0.9 to 4.87 % for PVC/CAB blends. The polymer blend with higher CAB content showed maximum degradation ( Fig. 2a and 2b). The results comparatively showed higher degradation than any other methods used maybe because of the combined effect of microbial degradation and hydrolysis [20,21].

Enumeration of bacteria during degradation
The control and test samples containing polymer blends were examined at intervals of ve days for 30 days (Fig. 3). The bacteria recovery in control showed exponential growth than test samples. The bacterial count was about 5.1×10 5 CFU/mL for control on the fth day while test samples remained below 2.1×10 5 CFU/mL. A gradual increase in bacterial count in test samples was noticed with an increase in days. Killing e ciency between the test sample and control showed no signi cant difference. This point out that present blend polymer is comparatively stable up to fteen days, thereafter due to regeneration capability of bacteria the bacterial count increases in remaining days. Even signi cant changes in the pH of the test solutions were observed. The initial pH value of 7.0 ± 0.2 was reduced to 6.8 in 30:70 (PMMA/CAB) systems. Similar results were obtained for PVC/CAB blends.

Enumeration of the enzyme during degradation
The BH medium was taken in ve sets of Erlenmeyer asks and commercially available enzyme lipase was used for the e ciency studies. 250 mL of BH medium + 250 units per 10 mL of lipase was dissolved in phosphate buffer. The bacterial count was done at a regular interval of ve days. As the enumeration of bacteria data during degradation the enumeration of the enzyme showed a similar increase in the bacterial count with an increase in days. The overall mechanism of enzyme and bacteria degradation of polymer blends is shown in scheme 1. 1 H NMR analysis of blend polymer degradation Table 1 shows the functional groups of the before and after biodegradable polymers, respectively. The 1 HNMR spectra of before and after degradation samples are shown in Fig. 5a for pure CAB, Fig. 5b for 30:70 PMMA/CAB, Fig. 5c for 50:50 PMMA/CAB, Fig. 5d for 30:70 PVC/CAB. PMMA is a proton acceptor polymer and CAB is a proton donor polymer and they are found to be miscible due to hydrogen bonding.
Before degradation, as per the CAB structure point of view, four ester groups are present in the 6, 3, 2 and 7 positions. One more ester group is formed due to blending with PMMA. These ester groups show multiplet peaks between 0.10 to 2.5 ppm. The CH 2 aliphatic protons can be observed between 2.19 and 2.29 ppm. Another acetylenic proton peak is observed between 2.19 and 2.29 ppm. The aliphatic methylene (CH 2 ) peaks are noticed at 1.1 and 1.6 ppm and the methyl protons peaks are observed at 0.86 ppm. The peak at 3.5 ppm is due to vinyl compounds [13,16,23,24]. After 15 days of biodegradation plenty of small peaks are observed in the region of 1.5 to 5, because of the breakage of long-chain polymers and hydrolytic degradation of esters into CO 2 and H 2 O.

Conclusion
The problem of least understood biodegradation of synthetic polymer when blended with natural polymer is solved in this paper. The weight loss, bacterial, enzymatic methods were used to study biodegradation of blend polymers. The results obtained from FTIR, NMR and GPC indicated positive response for biodegradation of blend lms in which the content of CAB in more. Moreover, pure CAB partially degraded probably because of the reduced number of free hydroxyls enhanced the interaction with water and inhibited enzymatic hydrolysis. Whilst, in less water containing solid culture medium, synthetic polymer blended CAB showed biodegradation.