Abstract
Cornstarch is a preferable raw material in the production of biodegradable plastics. Five composites of a modified (by acylation) cornstarch plastic were tested for the biodegradability in four soils collected from sites namely, Ama, Taketoyo, Shinshiro, and Hekinan of Aichi prefecture in Japan. The plastics slightly differedfrom each other in chemical composition. The degradation was evaluated quantifying the weight loss by combustion after burying the sheets (3cm×3cm) of plastic in soil, and retrieving periodically over 18-48 weeks. The plastic L, which composed of 83 paper, exhibited an average degradation of 79% by 18 weeks. The thin laminated resin film of it was brittle with loss of strength. The plastics S and MS with short acyl groups degraded 45% and 40% respectively. The plastics PF and 2V with both short and long acyl groups degraded only 6% and 1 .2% respectively. This resistance to degradation was supposed to be due to the presence of long acyl groups in the polymer. Prolonged incubation up to 48 weeks, exhibited great deterioration. The degradation did not significantly depend on the physico-chemical characteristics of soil.
