Degradation of starch-filled polyethylene films in a composting environment

Studies were made of the microbial degradation of a series of low density polyethylene films filled with different amount of starch in the range 0-40% by weight. Biodegradability was evaluated by three different procedures of exposure of test samples to microbial attack in which the samples were either maintained in active composting piles, or aerobically incubated in the liquid obtained by pressing the initial composting material, or treated in a minimal mineral medium inoculated with a thermophilic actinomycete isolated from samples retrieved from compost. Spectroscopic analysis and optical and electron scanning microscopy, as well as dynamic-mechanical properties, molecular weight, and weight loss of the retrieved samples were utilized for a semiquantitative evaluation of microbial attack. The results indicate that the composting microbial ecosystem seems to be the most efficient degradative environment among the three systems, although this conclusion may hold only for the polymer sample containing 40% starch.