Polypropylene/ethylene-co-propylene blends: influence of molecular structure of EPR and composition on phase structure of isothermally crystallized samples

Abstract

The structure of phases and interphases in samples crystallized under controlled undercoolings, of isotactic polypropylene/ethylene-co-propylene copolymers (iPP/EPR blends) was examined using optical and electron microscopy and small-angle X-ray scattering and differential scanning calorimetry. The study was undertaken to establish the influence of molecular structure of the EPR copolymers and blend composition on the phase structure developed in samples isothermally crystallized at relatively low undercoolings. Optical and electron microscopy revealed that the molecular structure and composition of the EPR phase play a predominant role in determining the mode and state of dispersion of the minor rubber component. It was also found that the crystallization process of iPP from its blends was influenced by the presence of the EPR phase with no regular dependence on its molecular structure and composition. For a given crystallization temperature, a decrease in thickness of the crystalline lamellae,L _c, and an increase in the amorphous interlamellar layer,L _a were observed. TheL _c andL _a values were found to be strictly related to the blend composition;L _c decreasing andL _a increasing with increasing EPR content in the blend.