Simulation of Coextrusion Flows of Polymer Melts

Coextrusion of flat films and sheets involves the simultaneous extrusion from a single die of multiple layers of polymer melts. Multilayer coextrusion provides an important approach to provide unique product properties through the selection and combination of different polymers within one product. Two families of dies include manifold dies, where the melts meet outside the die, and feedblock dies, where the melts flow in contact within the die cavity. In feedblock type dies, the problems of layer nonuniformity and interfacial instability have received considerable attention in the literature. Recent experimental and computational results have shown that layer nonuniformity (sometimes referred to as encapsulation) is affected by the viscosity and flowrate ratios of the polymer melts, die geometry and normal stress differences. Instability at the interface is also affected by the same quantities, but the elastic contributions are not as clearly understood. This article reviews recent progress in the simulation of flat die coextrusion.