Influence of EP/PP viscosity ratio on the surface morphology and elasticity of injection moulded PP/EP

The influence of the viscosity ratio between (ethylene-propylene) copolymer (EP) and polypropylene (PP) on the EP surface distribution in injection moulded disks of PP/EP resins has been investigated by transmission electron microscopy (TEM) and by atomic force and force modulation microscopies (AFM and FMM). TEM images taken on transverse sections parallel to the injection direction reveal that, for high EP/PP viscosity ratios, large (>1 mu m) undeformed EP nodules are observed up to the surface. The AFM and FMM observations performed on the surface reveal soft regions of the same size embedded in a more rigid matrix (undeformed EP nodules present at or just below the surface). For low viscosity ratios, EP rubber nodules, strongly elongated parallel to the surface, are observed by TEM. From FMM measurements, the elastic modulus is found to be homogeneous across the surface and is comparable to that measured above EP nodules on the high viscosity ratio resin. (C) 1999 Society of Chemical Industry