Hydrolytic degradation of films prepared from blends of high and low molecular weight poly(DL-lactic acid)s.

Biodegradable films were prepared by casting acetone solutions of mixtures of a high molecular weight poly(DL-lactic acid) (HMW-PLA50) with 0, 10, and 30% w/w poly(DL-lactic acid) oligomers (LMW-PLA50), before drying. From size exclusion chromatography (SEC) it was shown that degradation occurred during film processing, in agreement with the acid-catalyzed degradation of polyesters. The higher the content of LMW-PLA50, the larger the decrease of the molar masses. The three selected film formulations were then allowed to age in isoosmolar 0.13M, pH 7.4 sodium phosphate buffer at 37 degrees C. The hydrolytic degradation was monitored by using various techniques, namely weighing to quantify water absorption and weight loss, SEC to evaluate molar mass changes, head space gas chromatography to assess the desorption of residual acetone, and enzymatic assay of the L-lactic acid released in the aging media. The presence of LMW-PLA50 clearly accelerated film degradation. Moreover, it was shown that the mechanism of degradation greatly depended on the content in the oligomers.