(467i) Finite Element Analysis of Multilayer Coextrusion

Multilayered coextrusion combines different polymers into a layered structure, which produces a composite material that has the union of properties from each of the material subcomponents. In this way, materials can be made that have much improved properties over single polymer extrudates. Current applications of multilayered coextrusion include packaging, protective coatings and barriers. For instance, these can be used for products such as soft drink bottles, which use an oxygen impermeable layer adhered to a carbon dioxide impermeable layer. This technique is also being explored for new technologies such as energy storage devices, sensors, displays and membranes. In our work, we are investigating multilayer coextrusion as a means to produce many-layered, nanoparticle-filled polymer structures for use as sensors or energy storage devices. These devices must have an offset to their layered structure such that one polymer essentially encapsulates the other polymer. Creating such an offset is not currently done commercially and is thus a research issue.

To aid the manufacturing process, we are developing computational models of coextrusion to look at potential die designs to create an offset structure and issues such as layer non-uniformities and instabilities. Instabilities due to property differences between layers, such as viscosity and elasticity, and instabilities associated with flow geometries can plague coextrusion processes. Models of varying degrees of complexity are investigated, though we limit ourselves to Newtonian rheology. Numerical models of the multilayer coextrusion process are developed based on a finite element discretization and an arbitrary-Lagrangian-Eulerian (ALE) moving mesh implementation to understand the moving boundary problem associated with the polymer-polymer interface. We have undertaken linear stability analysis in 2D to understand possible ribbing and barring instabilities. We have also built a full 3D model to examine a die design that would allow for offset between the coextruded layers and produce the necessary encapsulated phase for our project. In addition, particle tracking is investigated as an approximate method to determine layer thickness from a steady, single-fluid simulation.

* Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.