This study deals with six TPO blends that show different degrees of severity of flow lines (tiger striping) upon injection molding. Of these, the surface morphology of two reactor made TPO blends was examined in detail following injection molding. Strain rate dependent extensional viscosity curves of the components of all blends were determined using skin-core flow through a semihyperboloidal die in a capillary rheometer. In addition, the longest relaxation times of the blend components were determined using dynamic mechanical testing in a parallel plate fixture. These data have been used to identify the most relevant factors determining the severity of tiger striping. The results reveal that lowering the viscoelasticity of the dispersed phase relative to the matrix is key to controlling the severity of tiger striping.
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