CHARACTERIZATION OF THE DEGRADATION OF POLYLACTIC ACID POLYMER IN A SOLID SUBSTRATE ENVIRONMENT

Polylactic acid (PLA) polymer film was degraded in abiotic and biotic environments to understand the role of microbes in the degradation pro cess of lactic acid based polymers. The degradation studies were condu cted in a well-characterized biotic system, an abiotic system, a steri le aqueous system; and a desiccated environment maintained at 40, 50, and 60 degrees C. The combination of experiments in different environm ents isolated the distinct effect of microbes, water, and temperature on the morphological changes in the polymer during degradation. Due to lack of availability of radiolabeled PLA, various analytical techniqu es were applied to observe changes in the rate and/or mechanism of deg radation. CO2 evolved, weight loss, and molecular weights were measure d to evaluate the extent of degradation. X-ray diffraction and differe ntial scanning calorimetry techniques monitored the morphological chan ges in the polymer. FTIR was used as a semiquantitative tool to gather information about the chemistry of the degradative process. Neither o f the above analytical techniques indicated any difference in the rate or mechanism of degradation attributable to the presence of microorga nisms. The extent of degradation increased at higher process temperatu res. FTIR data were evaluated for significant statistical difference b y t-test hypothesis. The results confirmed hydrolysis of ester linkage as the primary mechanism of degradation of PLA. On the basis of these data, a probable path of PLA degradation has been suggested.