The crystallization and morphology of melt-miscible polymer blends

Abstract

The morphology and kinetics of crystallization from melt-miscible blends is reviewed for binary systems in which either one or both polymer components are crystallizable. In systems in which one component (component A) crystallizes first, the other component (B) may reside finally between spherulites, between growth arms (composed of a stack of A crystalline lamellae), or between crystal lamellae of A. The kinetics of component redistribution dictates which site must become primary. It is shown that the diffusivity D of the components in the melt and the velocity V of spherulite growth combine through the diffusion length d = D/V to define the final location for component B and to also define whether spherulite propagation will be linear or parabolic in time. When crystallization of both components proceeds concurrently, by forming spherulites of A and of B, the spherulites are prone to interpenetrate or to form concentric spherulites. Cooperative crystallization, in which the kinetics of a rapidly crystallizing component and a slowly crystallizing component are both affected such that the two crystallize nearly simultaneously, is discussed. Finally, the competition between liquid-liquid phase separation and crystallization in systems with either an upper or lower critical solution temperature is reviewed.

Keywords

blends / crystallization / morphology