BIODEGRADABILITY OF MODIFIED PLASTIC FILMS IN CONTROLLED BIOLOGICAL ENVIRONMENTS

The disposal of over 10 million tons of plastic per year in the United States has raised the demand for "degradable" or "biodegradable" plastics as a means of reducing the environmental impact of these materials. Unfortunately, the promotion of the "degradable" concepts has evolved in the absence of standard tests and definitions. The biodegradabilities of 12 modified plastic films were tested by exposing the films to controlled and highly efficient microbial degrading anaerobic and aerobic bioreactors. Extended biochemical oxygen demand (BOD) testing was also used to assess film biodegradability. Two photodegradable films were exposed to sunlight prior to BOD testing. Mass loss after bioreactor exposure and BOD exertion, which were strongly correlated, were used to assess biodegradability. Films containing starch showed no evidence that anything other than the starch component was biodegraded, despite, in two cases, disintegration caused by prooxidant activation. The mass of the starch addition and BOD exertion were strongly correlated. Sunlight exposure of photodegradable films caused significant disintegration of the films, but did not render the film fragments biodegradable. Only one test film, a poly(hydroxybutyrate)poly(hydroxyvalerate) copolymer, showed evidence of substantial biodegradation.