Biodegradability studies of HDPE/PLLA blends under controlled composting environment

Abstract

Degradation of plastics, especially those used in flexible packaging and similar other applications is necessary to prevent environmental pollution by littering of these plastics after their use. To make polyethylene degradable, blending with biodegradable polymers such as poly(L-lactic acid) (PLLA) is required, which facilitates the enzymatic degradation of the blends by the microbes present in compost and/or soil. In the present research, biodegradability of eight different HDPE/PLLA blend samples i.e. with compatibilizer (X1, X2, X3 and X4) and without compatibilizer (B1, B2, B3, and B4) were studied as per the guidelines of ASTM D 5338-98 (modified) standard. One gram approx by weight of each sample was taken for carrying out the experiment. The conditions required for the degradation in composting environment were optimized such as temperature, humidity, and flow rate of CO2-free air etc. The properties of the municipal compost used were also analyzed; viz. N2 content and C/N ratio which will facilitate the growth of the microbes responsible for the polymer blend degradation. The biodegradability testing apparatus, to carry out the experiments, was designed and developed according to the guidelines of the mentioned standard. The CO2 evolved was measured as a function of time and the percentage of biodegradability was obtained by determining the percentage of carbon in the test substance that is converted to CO2 during the duration of the test. It was found that after 45 days of test period, the percent biodegradability of blend X4 was maximum i.e. 3.5% and minimum i.e. 1.84% for negative (HDPE) as compared to positive control (MCE) i.e. 16.5%. After degradation period, weight loss and protein estimation of X4 was found to be maximum i.e. 2.54% and 0.773 gm/ml respectively. In conclusion, the blend may be considered as ‘safe’ for disposal through solid-waste composting plants.