Effect of Multiple Extrusion on Impact Fracture of Three Poly(propylene) Impact Copolymers



The effect of structural changes induced by multiple extrusion on the impact fracture behavior of three reactor poly(propylene) impact-copolymers (ICPPs) was investigated. The morphogenesis of the complex ICPP structure was controlled by the competition between the intraspherulitic phase separation and crystallization. The rubbery inclusion size was controlled by the rate of spinodal decomposition at the onset of crystallization. The following fast spherulite growth fixed the size and spatial distribution of these inclusions. The Charpy notched impact strength (ak) and critical strain energy release rate (Gc) measured under impact loading decreased significantly with the number of extruder passes. A measurable reduction of the size of the crack tip plastic zone (Rp) with the number of extruder passes was observed using high speed digital camera. While the melt flow index (MFI) dependence of ak exhibited ICPP specific shape, the MFI dependences of Gc fell on a single master curve at both 23 and −20 °C.