Marine microbe-mediated biodegradation of low- and high-density polyethylenes

Unpretreated and thermally pretreated low- and high-density polyethylenes (LDPE and HDPE) and unpretreated starch-blended LDPE were subjected to in vitro biodegradation. In this study two marine micro-organisms were selected, specifically Bacillus sphericus GC subgroup IV and Bacillus cereus subgroup A, for a duration of 1 year, at pH 7.5 and temperature 30 °C with the polymer as the sole carbon source. FTIR spectrum showed that initially carbonyl index increased, probably due to oxidation by dissolved oxygen (abiotic factor). Prolonged exposure to organisms led to decrease in carbonyl index due to biodegradation (biotic) through Norrish-type mechanism or through the formation of ester. The weight loss of the thermally treated LDPE and HDPE samples were about 19% and 9% respectively, and unpretreated samples were 10% and 3.5% respectively with B. sphericus in 1 year. Weight loss of unpretreated starch-blended LDPE was 25% with B. cereus. Tensile strength of thermally pretreated LDPE and HDPE and unpretreated starch-blended LDPE decreased by 27%, 14.8% and 30.5%, respectively, with B. sphericus and the corresponding decrease in crystallinity was 8%, 2.2% and 8.5%, respectively. Decrease in contact angle indicated that the surfaces turned more hydrophilic after exposure. Surface morphological changes of the biological-treated samples were observed by atomic force microscopy.