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Sheet coextrusion of polymer solutions and melts: Comparison between simulation and experiments

Coextrusion flows of polymer solutions and melts to produce polymeric sheets are studied employing (a) the Lubrication Approximation Theory for a quick determination of interface development and pressure drops for each material; and (b) the Finite Element Method, which uses a u-v-p-T-h formulation for the velocities, pressures, temperatures, and interface location and solves in the flow domain the full conservation and constitutive equations. The determination of the interface is part of the solution process. Simulations have been carried out for several cases of two-layer coextrusion of polymer solutions (Oppanols, i.e., polyisobutylenes) and compared with experimental data available in the literature. A three-layer coextrusion case is also studied with a barrier ethylene vinyl alcohol and an adhesive layer tying a polystyrene layer, and the results are compared with experimental data. For low flow rates, the interface location agrees closely with experiments. For high flow rates, a tendency for encapsulation occurs, which cannot be captured by the present purely viscous two-dimensional simulations. © 1993 John Wiley & Sons, Inc.