Hierarchy structure in injection molded polypropylene/ethylene-octane copolymer blends

In this article, the phase morphology and mechanical properties of polypropylene (PP)/ethylene-octane copolymer (POE) blends with fixed ratio (60/40) obtained via different processing conditions, including barrel temperature, injection speed, and mold temperature, have been investigated. SEM was carried out for detailed characterization of phase morphology from the skin to the core, layer by layer. It was interesting that for all the processing conditions no dispersed POE elastomer was observed in the skin layer but elongated POE particles with large size were observed in the subskin layer. From the transition zone to the core layer, an increased phase separation was observed, which could lead to a formation of cocontinuous morphology, depending on the processing condition used. Higher barrel temperature, lower mold temperature, and higher injection speed could result in a smaller size of POE phase. The tensile strength and impact strength were found not sensitive to barrel temperature and mold temperature but to the low injection speed, both tensile strength and impact strength had a higher value forspecimen obtained via low injection speed. The formation of the skin-core morphology and the effect of processing conditions on the phase morphology were discussed based on crystallization kinetics of PP matrix, rheology, and shear induced phase mixing. (c) 2007 Wiley Periodicals, Inc.