Crazing and shear yielding in polypropylene

Abstract

Crazing and shear yielding are essentially the two main modes of deformation which are responsible for brittle and ductile fractures of all polymers, respectively. However, craze-like features, as those in amorphous polymers, have been observed in crystalline polymers for a long time, but crazing in polypropylene (PP) is still not completely understood. One basic problem of studying crazing in crystalline polymers, such as PP, is the fact that they are normally organized into various microstructures, such as spherulites, consisting of lamella-type crystal and interlamellar amorphous regions (see’spherulitic crystallization and structure’ in this book). Another basic problem is that, at room temperature, crystalline polymers are above their glass transition point and they tend to deform and to yield without forming crazes. Such typical deformation is frequently found in plane stress tensile tests at room temperature. Hence, it has not been believed for a long time that crazing can be a dominant deformation mode in PP.