BIODEGRADABILITY OF POLYHYDROXYBUTYRATE(CO-HYDROXYVALERATE) AND STARCH-INCORPORATED POLYETHYLENE PLASTIC FILMS IN SOILS

Given the extremely low rates of microbial decomposition of most common plastics, the manufacture of biodegradable plastics is of interest as a means of managing the solid waste stream, as well as for specialty applications in pharmaceuticals and agriculture. In order to evaluate the biodegradability of several plastics commercially developed for enhanced biodegradability, plastic films of two types- (i) polyhydroxybutyrate copolymerized with hydroxyvalerate (PHBV) and (ii) low density polyethylene (LDPE) incorporated with a starch filler-were incubated for 44 d under moist, aerobic conditions in two soils, an acid sand and a calcareous sandy loam. Biodegradability of the plastics was evaluated based on evolution of CO2-C upon incubation and by microscopic examination after 44-and 150-d incubation under the same conditions. Biodegradation of polyhydroxybutyrate films ranged from 5% to near complete biodegradation during the 44-d incubation, depending on soil type, film thickness, and the nature of chemical additives to the polymer. Granules of embedded starch exposed at the surface of starch-incorporated polyethylene films were degraded within 14 d, after which no further biodegradation could be detected; no gross deformations of the plastic film were associated with the loss of surface starch.