A novel model of polymer flow with processing aid (PPA) is developed to predict the start-up of pressure transient in capillary flow. The gradual coating dynamics of the die surface with PPA are predicted with the pressure transient and the gradual change in polymer slip velocity. This model includes several physical parameters that can lead to developing/identifying appropriate polymer processing aids and optimizing them in terms of concentration, performance, and operational conditions. The model is validated using experimental results to address the effects of die length, apparent shear rate, and PPA (fluoropolymer) concentration on the flow dynamics and melt fracture performance of PPAs.
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