A Model for Predicting Slip Velocity during Extrusion with Fluoropolymer Processing Additives

A molecular model, based on the concept of the activation rate theory, is developed for slip of a polymer as it flows through a die. The model correctly predicts the dependence of the apparent slip velocity of high molecular weight, linear polyethylene resins on wall shear stress, up to the onset of gross melt fracture. It also predicts the increased slip which occurs when die surfaces are coated with a fluoropolymer processing aid having a low surface tension.