Thermal degradation and biodegradability of poly (lactic acid)/corn starch biocomposites

Thermal degradation and biodegradability of poly (lactic acid) (PLA) and poly (lactic acid)/corn starch (PLA/CS) composites with and without lysine diisocyanate (LDI) were evaluated by thermogravimetric analysis measurement and enzymatic degradation using Proteinase K and burial tests, respectively. Thermal stability was decreased by addition of CS and the composites with LDI showed higher thermal degradation temperature than those without LDI. In enzymatic biodegradation, the weight remaining of all samples decreased almost linearly with time. The addition Of CS resulted in a faster rate of degradation and the composites with LDI were more difficult to degrade than those without it. In the composite without LDI, the degradation was faster at the interface between PLA and CS, showing deep and wide clearance, but degradation starting at the interface was not clearly observed in the composite,with LDI. There was no considerable difference in molecular weight and distribution of the samples after enzymatic degradation. The lactic acid content of the water-soluble product obtained after enzymatic degradation increased with degradation time. In burial tests, pure PLA was little degraded but the composites gradually degraded. The degradation of the composite Without LDI was faster than that of the composite with LDI. (c) 2006 Wiley Periodicals, Inc.