Effective multi-stage biodegradation of commercial bulk polyurethane by Clonostachys and Purpureocillium spp

Dealing with plastic waste in an environmentally friendly and effective manner has been a conundrum that much research has attempted to address. An attractive approach is biodegradation by microorganisms; however microorganisms that have shown such potential are generally only able to degrade surface layers of polymer materials. Herein we describe the multi-stage degradation of commercial bulk polyurethane by two strains of fungi isolated from a landfill. Moreover, we demonstrate that the mechanisms of degradation are not hydrolysis alone as is usually reported, but decarboxylation as well. The data presented here suggest that chain scission at urethane groups involves hydrolysis and decarboxylation of the terminal functional groups and the release of CO₂. Two strains, Clonostachys sp. PB54 and Purpureocillium sp. PB57 were both able to decrease the mass of commercial bulk polyurethane by 40 % after 90 days. Spectroscopic analysis revealed the breakage of urethane and ester linkages but also detected variations in hydrogen bonding over time, indicating initial degradation of amorphous surface regions followed by destabilization of more ordered, crystalline layers. Subsequent Liquid Chromatography Mass Spectrometry (LCMS) analysis demonstrated that the fungi were capable of liberating monomer-equivalent molecules (4,4'-methylenedianiline) from the bulk material. In this work, these fungi are shown to be capable of significantly degrading commercial bulk polyurethane in a short period of time, producing small organic molecules and CO₂, and as such, are good prospects for the development of large-scale plastic biodegradation processing.