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 effects 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 buffer 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.