Die lip buildup and polymer rotarance theory

Abstract

Die drool is the unwanted accumulation of material spilling onto the open faces of an extrusion die. In this paper, we explore the intriguing roles of subtle batch to batch variations in nonlinear viscoelasticity and molecular structure on the dimensionless buildup. Specifically, we view the behaviors of high and low dimensionless buildup resin batches through the lens of sudden inception of steady shear flow, both measured and predicted by rigid bead-rod theory. We find that the high drool rate high-density polyethylene film resin exhibits higher shear stress upon sudden inception of steady shear flow than its low drool counterpart. We further find that both high-density polyethylene film resins, examined through the lens of rotarance theory, behave as suspensions of multi-bead rods (also called shish kebabs). Both high-density polyethylene film resins exhibit the same longest relaxation time, the same macromolecular moment ratios, and differ only in their Weissenberg numbers, and thus, in their amounts of nonlinear viscoelasticity.