Rapid (bio)degradation of polylactide by mixed culture of compost microorganisms - low molecular weight products and matrix changes

Poly(L-lactide) (PLLA) was rapidly (bio)degraded by a mixed culture of comp ost microorganisms. After 5 weeks in biotic environment, the films had frag mented to fine powder, while the films in corresponding abiotic medium stil l looked intact. Analysis of the low molecular weight products by GC-MS sho wed that microorganisms rapidly assimilated lactic acid and lactoyl lactic acid from the films. At the same time, a new degradation product, ethyl est er of lactoyl lactic acid was formed in the biotic environment. This produc t cannot be formed by abiotic hydrolysis and it was not detected in the abi otic medium. The degradation of the PLLA matrix was monitored by differenti al scanning calorimetry (DSC), size exclusion chromatography (SEC) and scan ning electron microscopy (SEM). A rapid molecular weight decrease and incre asing polydispersity was observed in the biotic environment. In the abiotic environment only a slight molecular weight decrease was seen and the polyd ispersity started decreasing towards 2.0. This indicates different degradat ion mechanisms, i.e. preferred degradation near the chain ends in the bioti c environment and a random hydrolysis of the ester bonds in the abiotic env ironment. SEM micrographs showed the formation of patterns and cracks on th e surface of the films aged in biotic medium, while the surface of the ster ile films remained smooth. The SEM micrographs showed a large number of bac teria and mycelium of fungi growing on the surface of the biotically aged f ilms. (C) 1999 Elsevier Science Ltd. All rights reserved.