Effect of nucleating agent on the structure development in isotactic polypropylene/liquid paraffin mixture

Abstract

We investigated the crystallization behaviour in an isotactic polypropylene (PP)/liquid paraffin (LP) mixture loaded with a small amount of nucleating agent (NA) under a microscope. Three types of crystallization behaviour were observed, depending on the crystallization temperature and the composition: (1) connected nucleation (CN)-type crystallization which yields a unique network structure consisting of interconnected PP crystals; (2) aggregated nucleation (AN)-type crystallization; and (3) the familiar spherulitic crystallization. The CN and AN types were never observed in binary mixtures of PP/LP and PP/NA. In contrast, the NA/LP mixture developed a network structure consisting of highly interconnected axialite-like crystals of NA. The crystallization mechanism in the ternary mixture (PP/LP/NA) was found to be controlled by the competitive kinetics of the NA crystallization versus that of PP; e.g., the network structure is created when NA crystallization occurs and then small PP crystals grow densely along the fibrils in the axialite NA crystals. © 1990.