Molecular ordering and α′-form formation of poly(l-lactide) during the hydrolytic degradation

Hydrolytic degradation ability is an intriguing characteristic of poly(l-lactide) (PLLA) and it has been intensively investigated recently. However, the microstructure evolution of PLLA during the early stage of the hydrolytic degradation process is neglected. In this work, amorphous PLLA was hydrolyzed in alkaline media at temperatures from 40 to 60 °C. The variations of weight loss and molecular weight were measured to study the degree of the hydrolytic degradation of PLLA. The effect of hydrolytic degradation on microstructure of the amorphous PLLA was investigated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscope (FTIR), wide angle X-ray diffraction (WAXD) and scanning electron microscope (SEM). The results clearly proves the occurrence of molecular ordering and the formation of α′-form PLLA, which is greatly related to the hydrolytic degradation conditions. At relatively low hydrolytic degradation temperature (40 and 50 °C), locally ordered structure is provoked, while a large number of α′-form crystallites are induced at relatively high temperature (60 °C). This work is very significant in understanding the microstructure evolution of PLLA during the hydrolytic degradation process.