Study on characteristics of paper laminated with biodegradable plastics, 2. Analytical characterization on chemical and biological degradation

Chemical and biological degradation behavior of commercial polylactide (PLA) film, poly (L-lactide) (PLLA) and poly (DL-lactide) (PDLLA) was investigated by gravimetric analysis, X-ray diffractometry, differential scanning calorimetry and Fourier transform Raman (FT-Raman) spectroscopy. The PLA film exhibited an extremely high resistance to acid hydrolysis by hydrochloric acid, although alkaline treatment with a dilute sodium hydroxide brought about the quick decomposition of PLAs, not being reflected in their crystallinity. The X-ray and FT-Raman results implied the immediate decomposition occurring only on the PLA surfaces. These phenomena were observed both for crystalline PLLA and amorphous PDLLA; however, at temperature above their glass transition points, the PDLLA was greater deteriorated than the PLLA under acidic conditions, whereas in the alkaline system the tendency was reversed. On the biological degradation, the PLA film remained almost unchanged even after buried in soil for six months, as supported by various analytical results. Possibly, the PLA-related products commercially available have lower biodegradability than expected, and thus it was indicated that a strategic material design, e.g., the utilization of paper-based ecomaterials whose practicality and biodegradability can be compatible with each other, is of significance for high performance composite-manufacturing with biodegradable plastics.