Effects of physical aging on glass transition behavior of poly(dl-lactide)

Poly(dl-lactide) (PDLLA) was physically aged at room temperature and the changes in glass transition behavior were investigated by means of differential scanning calorimetry (DSC). It was found that in the glass transition region of PDLLA, the physically aged specimens have two endothermic transitions in their DSC heating curves. In general, the peak located at lower temperature was stronger, but an example that the magnitude of the higher temperature peak is stronger was found in the study. With increasing aging time, the starting and ending temperatures of transition together with the peaks shift to higher temperatures, the magnitude of the two peaks increase, the region of transition reduces, and the lower temperature peak is more close to the higher temperature one. The endothermic peaks increase faster in the initial period (2–6 d) of physical aging. Hydroxyapatite has no marked influence on the transition behavior of PDLLA during aging. The experimental results were discussed and explained according to the viewpoint of cohesional entanglement.