Microstructural aspects of surface deformation processes and fracture of tensile strained high isotactic polypropylene

Microstructural evolution during tensile deformation of high isotactic homopolymer polypropylene is examined as a function of strain and strain rate by scanning electron microscopy (SEM) and atomic force microscopy (AFM). At lower strain and strain rates, deformation bands nucleate on the surface, which on continued deformation develop into an array of closely spaced crazes, and multiply and grow inwards with increase in strain and strain rate. The final mode of fracture is a combination of crazing/tearing and brittle. AFM studies indicate that crazing and tearing involves alignment, merging and splitting of fibrils, and the brittle mode of fracture is characterized by reorganization of the microstructure. The micro-mechanisms of deformation are summarized in terms of strain rate–strain diagrams.