A Practical Model for Predicting Interfacial Flow Instabilities in Polyamide-PE Film Coextrusions Containing Tie Concentrate Blends, 2008 PLACE Conference

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Interfacial distortions at polyamide-polyethylene interfaces in coextruded films were studied and correlated with rheological properties of individual polymers. Melt flow instabilities at polymer-polymer interfaces in a coextruded film creates a non-uniform surface that typically lowers clarity and gloss and increases bulk haze. A mathematical model was developed for estimating flow and rheological properties of individual polymers such as bulk-flow velocity, viscosity, and shear stress from basic material properties and film production parameters. The mathematical model results were verified by experimental results.

The test results suggest that interfacial instability is influenced by rheological differences between layers in a coextrusion. The degree of interfacial instability is further amplified as adhesive bonds are formed across the polyamide-tie layer interface. The optical clarity of coextruded films can be improved by minimizing the number of interfacial bonds and matching melt flow velocities and die-wall shear stresses of adjacent polymer melt streams at the mating or flow confluence point.