Viscoelastic Computational Modeling of Extruded Micro-textured Polymeric Films

AbstractThe feasibility of the production of reduced-coefficient-of-friction micro-textured polymeric films by continuous extrusion using micro-patterned dies made by nonconventional meso-scale micromachining methods has been reported in our previous study [1]. During continuous manufacturing of such polymeric films, the viscoelastic effects of polymeric melts (e.g., die swell) lead to a film micro-texture that is different from the micro-patterned die. Thus, computational studies based on viscoelastic models solved by finite elements methods (FEM) were conducted to predict the die micro-geometries that develop desirable micro-texture shapes. ANSYS Polyflow® was used in conjunction with Cross and Giesekus models to predict the pressure drop and shape/die- swell of isotactic polypropylene films for a rectangular-semicircular micro-pattern. An isothermal, 3-parameter Cross model led to accurate estimation of the pressure drop through the dies, but led to poor estimations of the dimensions of the extrudate. In contrast, a unimodal Giesekus model resulted in over-prediction of the pressure drop (∼ two-fold), but led to accurate prediction of the extrudate shape and size (within an error of 15%) due to the incorporation of viscoelastic effects