DEGRADATION OF HIGH-MOLECULAR-WEIGHT POLY(L-LACTIDE) IN ALKALINE-MEDIUM

To study the effect of molecular weight and morphology on hydrolytic d egradation, four poly(L-lactide)s (PLLAs) with average molecular weigh t of 3.0 x 10(5), 4.5 x 10(5), 6.5 x 10(5) and 3 x 10(6) were used, PL LA films with different morphologies were obtained by solution casting . Degradation of the films was performed at 37 degrees C in 0.01 N NaO H solution and this alkaline hydrolysis seemed to simulate well the re al case while offering significant acceleration of the degradation pro cess. Diverse microscopy techniques (light, polarizing and scanning el ectron) were used to study the surface change of morphology and erosio n of the PLLA films. Swelling was visualized by scanning electron micr oscopy, particularly on the spherulites, which were eroded from the ce ntre by hydrolysis. In the case of highly amorphous film, crystallizat ion took place as degradation proceeded. The reduction in transparency of PLLA films, measured by a spectrophotometer at 570 nm, was ascribe d to the increased density of spherulites. Differential scanning calor imetry revealed that the crystallinity of PLLA increased with degradat ion time, in accordance with accelerated spherulite formation.