Impact modified isotatic polypropylene with controlled rubber intrinsic viscosities: Some new aspects about morphology and fracture

Abstract

Abstract The influence of the molecular weight of the dispersed phase of ethylene–propylene rubber modified isotactic polypropylene (iPP/EPR) reactor blends was studied in a systematic way by varying their intrinsic viscosity (IV) from 1.7 to 6 dg/L while keeping the matrix melt flow rate (MFR) constant. Standard Charpy measurements were completed by a continuous analysis of the impact properties over a wide range of temperatures at fixed test speed. As expected, the higher the IV, the tougher the iPP/EPR blends. However, ductile–brittle transitions as key mechanical descriptors did not correlate linearly with M w , suggesting the macroscopic behavior of the blend to be controlled primarily by the morphology of the EPR particles. Moreover, strong correlations were found between impact mechanical properties, amount of stress‐whitening, and strength of the molecular relaxations estimated from dynamical mechanical analysis. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1702–1712, 2003