Kinetics of Nucleation and Growth of Crystals of Poly(l-lactic acid)

Abstract

Prediction of the supermolecular structure and properties of poly(l-lactic acid) requires in-depth knowledge of the relation between the conditions of melt solidification and the crystallization process. Crystallization involves primary crystal nucleation, which then is followed by crystal growth. Both processes require chain segment mobility at different length scales, and exhibit different temperature and cooling-rate dependencies, as described in this review. Following an introduction to polymer crystallization and general information about crystallization of poly(l-lactic acid), data are presented on the kinetics of primary crystal nucleation, covering a wide range of temperatures. Crystal nuclei formation in the glassy state requires completion of the glass relaxation process, as shown by enthalpy relaxation experiments. Discussion of the nucleation behavior is then followed by information about crystal growth rates, which reveal a bimodal temperature dependence as a result of the specific α′/α-crystal polymorphism. Throughout this review, the effects of molar mass and optical purity on the kinetics of nucleation and growth of crystals are discussed.