Influence of low molecular weight lactic acid derivatives on degradability of polylactide

Abstract

The presence of low molecular weight lactic acid derivatives in films enhanced the degradability of polylactide in a biotic medium. Two different biotic and abiotic series were investigated. The films used for the first abiotic and biotic series (a-1 and b-1 films) initially contained some lactic acid 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, while no molecular weight decrease was seen in the a-1 films aged in a corresponding abiotic mineral medium. The molecular weight for the a-2 and b-2 films without lactic and lactoyl lactic acid remained almost constant. Scanning electron microscopy micrographs 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. Gas chromatography and mass spectrometry analysis showed that lactic acid and lactoyl lactic acid were rapidly assimilated from the films aged in a biotic medium. New degradation products (e.g., ethyl ester of lactoyl lactic acid, acetic acid, and propanoic acid) were formed during aging in a biotic medium. Acetic acid and propanoic acid were formed as intermediate degradation products during the initial stages, but they were no longer detected after prolonged aging. The concentration of the ethyl ester of lactoyl lactic acid increased with aging time. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 228–239, 2000