Biodegradation of poly(l-lactide) (PLA) exposed to UV irradiation by a mesophilic bacterium

Abstract

Degradation of PLA was examined with a mesophilic bacterium, which was identified as Stenotrophomonas maltophilia LB 2-3. The PLA degradation activity of S. maltophilia LB 2-3 was accessed using the modified Sturm test. PLA lost molecular weight and tensile properties quickly when exposed to UV irradiation. The biodegradability of PLA was enhanced as UV irradiation was increased to 8 h and then decreased with a further increase in UV irradiation. This contrasted with the general expectation that longer UV exposure would lower the molecular weight of PLA and, thus, increase biodegradability. The same behavior was also observed when PLA degradation was carried out in compost. A brittle white solid which may be poorly assimilated by microorganisms was formed during UV irradiation and was thought to be at least, in part, responsible for the biodegradability behavior. The GPC chromatogram of PLA powder suspended in mineral medium with S. maltophilia LB 2-3 was higher in intensity than that without the strain in the low molecular weight region, but at the same time, the reverse was true in the high molecular weight zone, revealing that the cleavage of PLA molecules was accelerated by enzymes secreted by S. maltophilia LB 2-3.