P135: Degradation of the compostable plastic packaging material polylactic acid

Poly(lactic acid) (PLA) is a polyester susceptible to degradation on the contrary of conventional plastics. As PLA short shelf-life products are thrown away after their use and they have the potential to replace conventional plastics, monitoring degradability of PLA in different environment conditions and understanding degradation mechanisms are important. Aims of this study were to determine the relative importance of biological and chemical degradation of PLA; identify fungi as putative PLA degraders and assess impact of PLA on microbial communities.

PLA pieces were buried in compost and soil; and incubated in sterile water at different temperatures (25-55ºC) and recovered over different time intervals. To determine degradation, gel permeation chromatography and tensile strength measurements were performed. Molecular weight and tensile strength of PLA were unaffected at 25° and 37°C, started decreasing at 45ºC and showed the fastest rate of degradation at 55ºC. Temperature was determined to be a key parameter for PLA degradation. Rate of PLA degradation in compost & soil was compared with sterile water to decide the role of hydrolysis and microorganisms in PLA degradation. Degradation of PLA in compost was the fastest suggesting role of fungi on PLA degradation.

Putative fungal PLA degraders were isolated from surface of PLA pieces recovered from compost and soil at 25 and 50ºC, identified by ribosomal DNA sequencing. Terminal restriction fragment length polymorphism (TRFLP) was used for for community analysis.  Fungal community structure on the surface of PLA was found to have lower diversity with more variation than compost and soil.