Numerical modeling of multilayer film coextrusion with experimental validation

Computational fluid dynamics (CFD) using a finite volume technique and the volume of fluid method of interface tracking is used to model the production of polyester-based multilayered films via coextrusion. Experimental methods encompass both overall flow validation and secondary layer thickness validation. The interpretation of frozen die plugs and layer thickness measurements of unstretched cast films using chloroform washing are used for overall flow validation. For secondary layer thickness validation, layer thickness measurements via both white light interferometry and chloroform washing of stretched final film samples are presented. Good agreement between CFD results and both die plug structures and layer thicknesses from chloroform washing of cast film is observed. When investigating final film samples, there is a good agreement between CFD and white light interferometry, based on individual layer thickness calculations. However, the layer thicknesses from chloroform washing of final films are lower than those obtained from both CFD and white light interferometry. This is attributed to partial crystallization of the thinner polymer at the interface after stretching and heating the film. POLYM. ENG. SCI., 2014.