Crystallization kinetics of polylactide and its blends

The purpose of this research was first, to investigate a polymerization method to produce polylactides of desired molecular weights. The polymers PLA-L and PLA-DL produced were then utilized to make blends of semicrystalline/amorphous components. The compatibility of the blends was investigated by determining their Tg with a DSC. However, because of the proximity of the Tg's of the two components, a new approach , which utilized the effects of the "physical" aging on the the Tg peaks obtained by DSC was considered. The results obtained by this method showed that only three blends containing low molecular weight species were compatible. All the others, while incompatible, possessed a certain degree of partial miscibility.

The crystallization kinetics were investigated on the pure PLA-L and the blends. Two separate studies were conducted, the first on the kinetics of the overall crystallization by means of an Avrami analysis, the second on the growth rates of the individual spherulites. The kinetics of crystallization were found to decrease as the molecular weight of the semicrystalline component increased and as the PLA-DL content in the blend increased. In some particular cases, however, a spectacular increase of the growth rates was observed for high DL content blends. Optical microscopy showed that under these conditions, the spherulites grown, contained large inclusions of amorphous material.