Thanawadee Leejarkpai, Unchalee Suwanmanee, Yosita Rudeekit, Thumrongrut Mungcharoen
Center for Petroleum Petrochemicals and Advanced Materials, Department of Chemical Engineering, Faculty of Engineering, Kasetsart University, Bangkok 10900, Thailand. Italy.
This study models and evaluates the kinetics of C - CO2 evolution during biodegradation of plastic materials including Polyethylene (PE), PE/starch blend (PE/starch), microcrystalline cellulose (MCE), and Polylactic acid (PLA). The aerobic biodegradation under controlled composting conditions was monitorated according to ISO 14855-1, 2004. The kinetics model was based on first order reaction in series with a flat lag phase. A non-linear regression technique was used to analyze the experimental data. SEM studies of the morphology of the samples before and after biodegradation testing were used to confirm the biodegradability of plastics and the accuracy of the model. The work showed that MCE and PLA produced the high amounts of C - CO2 evolution, which gave readily hydrolysable carbon values of 55.49% and 40.17%, respectively with readily hydrolysis rates of 0.338 day-1 and 0.025 day-1, respectively. Whereas, a lower amount of C - CO2 evolution was found in PE/starch, which had a high concentration of moderately hydrolysable carbon of 97.74% and a moderate hydrolysis rate of 0.00098 day-1. The mineralization rate of PLA was 0.500 day_1 as a lag phase was observed at the beginning of the biodegradability test. No lag phase was observed in the biodegradability testing of the PE/starch and MCE. The mineralization rates of the PE/starch and MCE were found to be 1.000 day-1, and 1.234 day-1, respectively. No C - CO2 evolution was observed during biodegradability testing of PE, which was used for reference as a non-biodegradable plastics sample.