Influence of low molecular weight lactic acid derivatives on degradabilityof polylactide

The presence of low molecular weight lactic acid derivatives in films enhan ced the degradability of polylactide in a biotic medium. Two different biot ic and abiotic series were investigated. The films used for the first abiot ic and biotic series (a-l and b-1 films) initially contained some lactic ac id and lactoyl lactic acid, while the films used for the second abiotic and biotic series (a-2 and b-2 films) did not originally contain them. The b-1 films decreased in molecular weight during 3 weeks in the biotic medium, w hile no molecular weight decrease was seen in the a-1 films aged in a corre sponding abiotic mineral medium. The molecular weight for the a-2 and b-2 f ilms without lactic and lactoyl lactic acid remained almost constant. Scann ing electron microscopy micro-graphs showed a larger amount of bacteria and fungi growing on the surface of b-1 films compared to b-2 films; thus, the presence of easily assimilated lactic acid and lactoyl lactic acid in the films improved the initial growth of microorganisms on the film surfaces. G as chromatography and mass spectrometry analysis showed that lactic acid an d lactoyl lactic acid were rapidly assimilated from the films aged in a bio tic medium. New degradation products (e.g., ethyl ester of lactoyl lactic a cid, acetic acid, and propanoic acid) were formed during aging in a biotic medium. Acetic acid and propanoic acid were formed as intermediate degradat ion products during the initial stages, but they were no longer detected af ter prolonged aging. The concentration of the ethyl ester of lactoyl lactic acid increased with aging time. (C) 2000 John Wiley & Sons, Inc.