Demonstrating an ideal compostable plastic using biodegradability kinetics of poly(lactic acid) (PLA) based green biocomposite films under aerobic composting conditions

Abstract

This study demonstrates the kinetics of aerobic biodegradation of melt-extruded poly(lactic acid) (PLA) based biocomposite films by online monitoring of CO2 using gas chromatography technique following ASTM International D 5338–15 protocol. Biodegradation studies of PLA and its biocomposites were carried out in the presence of compost microbes, without the addition of any external inoculum. The first-order kinetics model was modified by incorporating a linear lag phase for each test sample. Bacterial identification by 16S rRNA gene sequencing showed Bacillus flexus as one of the microbes responsible for biodegradation of the exposed films at thermophilic temperatures. Neat PLA (NPLA) and PLA/Chitosan composite films were found to evolve high amounts of C–CO2 (carbon-to-carbon dioxide). C–CO2 conversion was found to be very low in PLA/cellulose nanocrystals and PLA/gum arabic biocomposites, expressing the presence of only 4% and 6% slowly hydrolysable carbon, respectively, as compared to NPLA and PLA/chitosan samples. The CCO2 evolution rate was the highest for PLA/chitosan sample at 1.13 day−1. Experimental data of all the test samples showed a good fit (R2 ~ 99.99) with the kinetic model. Morphological analysis by FESEM confirmed the erosion of polymer during composting.