Further investigations on the hydrolytic degradation of poly (DL-lactide)

The hydrolytic degradation of poly(DL-lactide)(PLA50)material was investigated in order to elucidate the e¤ects of temperature and acidity of the external medium on the degradation characteristics. It was observed that at 60¡C and at pH"7.4, degradation was extremely rapid as compared with degradation at 37¡C. After only 2 days, heterogeneous degradation was observed due to larger internal autocatalysis. On the other hand, in the case of degradation at 37¡C in an acidic medium with pH"3.7, the heterogeneous degradation was preceeded by a much longer lag time. Water absorption was found to be pH dependent. At pH"7.4, water absorption was increased due to the osmotic pressure driving the bu¤er solution into the polymer matrix to neutralize acidic endgroups, which was not the case for degradation at pH"3.7. In both cases, the oligomeric stereocomplex was obtained as degradation residue at the end of the degradation period.