Flow-induced solidification of high-impact polypropylene copolymer compositions : morphological and mechanical effects

Polypropylene-based impact copolymers are a complex composition of matrix material, a dispersed phase and many optional modifiers. The final heterophasic morphology of such systems is influenced significantly by the processing step, adding an additional level of complexity to understanding the structure-property relation. This topic has hardly been studied so far. The effect of thermal history and shear flow on the solidification process of three different compositions of a polypropylene-based impact copolymer, i.e., one base material and two compounds with either high density polyethylene or ethylene-co-octene added, is investigated. Samples are examined using differential scanning calorimetry, extended dilatometry, transmissions electron microscopy, and finally, tensile testing. With flow, the materials show pronounced flow-enhanced crystallization of the matrix material and deformed filler content. Compared to the base polymer, the stress–strain response of the compounded samples shows a lower yield stress and more pronounced influence of shear, reflected in the increasing strain hardening modulus.