Viscous and elastic effects in polymer coextrusion

Multilayer coextrusion is a process in which two or more polymers are extruded and joined together in a feedblock or die to form a single structure with multiple layers. These layers should be uniform in thickness across the structure for best performance. However, layer thickness nonuniformities have been observed in many coextruded products. Previous work has shown that these layer thickness variations can occur due to viscosity differences between the polymers in the layers and/or elastic effects that introduce secondary flows. The objective of this work is to examine the effect of viscous and elastic forces present in polyethylene coextrusion processes.