1993 Volume 50 Issue 1 Pages 19-25
A blend of impact-resistant poly (propylene-ethylene) copolymer and 20-30wt% of ethylene-propylene rubber (EPR) is widely used in the outer parts of automobiles. The properties of the material can not be fully explained on the basis of the generally accepted morphological model of polypropylene (PP) matrix and EPR domains. In this report, a morphological model composed of PP crystaline lamella domains distributed in a matrix consisting of networked amorphous PP and EPR is proposed, based on the detailed investigation by transmission electron microscopy (TEM), and visco-elastic and pulsed NMR measurements. This new morphological model reasonably explains several phenomena, such as the constancy of the impact strength and the elongation at break measured as a function of molecular weight of PP and the discontinuity in the Rockwell hardness and heat sag observed as a function of EPR content.
