Microstructural evolution during tensile deformation of polypropylenes

Tensile deformation processes occurring at varying strain rates in high and low crystallinity polypropylenes and ethylene–propylene di-block copolymers have been investigated by scanning electron microscopy. This is examined for both long and short chain polymeric materials. The deformation processes in different polymeric materials show striking dissimilarities in spite of the common propylene matrix. Additionally, the deformation behavior of long and their respective short chain polymers was different. Deformation mechanisms include crazing/tearing, wedging, ductile ploughing, fibrillation, and brittle fracture. The different modes of deformation are depicted in the form of strain rate-strain diagrams. At a constant strain rate, the strain to fracture follows the sequence: high crystallinity polypropylenes<low crystallinity polypropylenes<ethylene–propylene di-block copolymers, indicative of the trend in resistance to plastic deformation.