Influence of crystal and amorphous phase morphology on hydrolytic degradation of PLLA subjected to different processing conditions

Isothermal and non-isothermal crystallization kinetics of poly-l-lactide (PLLA) were studied in order to analyse the effect of crystalline and amorphous morphology on hydrolytic degradation. A modification of the nucleation/growing mechanism was observed in both isothermal and non-isothermal analysis. Samples isothermally crystallized at Tc<110°C showed a higher fraction of amorphous phase which does not relax at Tg. Lower and decreasing values of this 'rigid-amorphous phase' fraction were detected at higher crystallization temperatures (Tc>110°C). The effect of hydrolytic degradation on the amorphous and crystalline phases depends upon the initial morphology developed during the isothermal crystallization. The larger crystals developed at Tc=130°C are more resistant to erosion compared to the less perfect and smaller crystals developed at higher levels of undercooling (Tc=90°C).