Thermally induced crystallization and enzymatic degradation studies of poly (L‐lactic acid) films

Poly(L ‐lactic acid) (PLLA) films with different crystallinities were prepared by solvent casting and subsequently annealed at various temperatures (T_a) (80–110°C). The effects of crystallinity on enzymatic degradation of PLLA films were examined in the presence of proteinase K at 37°C by means of weight loss, DSC, FTIR spectroscopy, and optical microscopy. DSC and the absorbance ratio of 921 and 956 cm^?1 (A₉₂₁/A₉₅₆) were used to evaluate crystallinity changes during thermally induced crystallization and enzymatic hydrolysis. The highest percentage of weight loss was observed for the film with the lowest initial crystallinity and the lowest percentage of weight loss was observed for the film with highest crystallinity. FTIR investigation of degraded films showed a band at 922 cm^?1 and no band at 908 cm^?1 suggested that all degraded samples form α crystals. The rate of degradation was found to depend on the initial crystallinity of PLLA film and shown that enzymatic degradation kinetics followed first‐order kinetics for a given enzyme concentration. DSC crystallinity and IR absorbance ratio, A₉₂₁/A₉₅₆ ratio, showed no significant changes with degradation time for annealed PLLA films whereas as‐cast PLLA film showed an increase in crystallinity with degradation; this revealed that degradation takes place predominantly in the free amorphous region of annealed PLLA films without changing long range and short range order © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013