Isotactic polypropylene/ethylene-co-propylene blends: effects of composition on rheology, morphology and properties of injection moulded samples

Melt rheology, phase morphology and properties of (30/70) isotactic polypropylene/ethylene-co-propylene (iPP/EPR) blends, containing EPR copolymer synthesised by means of a titanium based catalyst with very high stereospecific activity (EPR sub Ti ), were compared to that of (30/70) iPP/EPR blends containing EPR copolymer synthesised by using a traditional vanadium based catalyst (EPR sub V ). It was found that both the melts are to be classified "negative deviation blends" and that, for such a composition ratio, the EPR represents the continuous phase. Scanning electron microscopy (SEM) investigations confirmed that the iPP component segregates in spherical-shaped domains with average size lower than 1.0 mu m. The presence of 70% of EPR copolymer dramatically interfered with the iPP crystallisation process, as strong reduction in iPP crystallinity index (X sub c ) values is shown by both the iPP/EPR blends. Wide angle X-ray scattering (WAXS) studies demonstrated that the EPR content determines the ratio between the apparent crystal size of iPP phase grown in a direction perpendicular to the (110) crystallographic plane and the apparent crystal size of iPP phase grown in a direction perpendicular to the (040) crystallographic plane. The higher the EPR content, the higher the thickness of the iPP lamellae in the direction of the radial growth of iPP spherulites, in agreement with increased nucleation density shown by DSC results. The different modulus performance shown by the materials at room temperature was accounted for by distinguishing between effects of phase crystallinity and super-molecular structure. Copyright (c) 2000 Elsevier Science Ltd