AbstractMelt spinning experiments were carried out to investigate the elongational behavior and fiber morphology of multiphase polymer systems. Materials chosen for study were blends of calcium carbonate‐filled polypropylene with general‐purpose polystyrene and blends of calcium carbonate‐filled polypropylene with high‐impact polystyrene. The former is a three‐phase system in which the CaCO3particles are dispersed, and the latter is a four‐phase system in which CaCO3particles are dispersed, together with rubbery butadiene particles. Note that polypropylene is incompatible with the matrix of high‐impact polystyrene. The experimental technique described in part I of this series was used to determine the elongational viscosity. With the four‐phase system, the apparent elongational viscosity tends to increase as the stretch ratio is increased above a certain critical value which appears to be ca. 25. This transition does not occur with the three‐phase system and is attributable to elongation of the suspended rubber particles. The addition of small amounts of HIPS to PP‐CaCO3increases spinnability in general, whereas larger amounts de
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