(with Savvas Hatzikiriakos)

Polytetrafluoroethylene (PTFE) is a high-melting-point polymer usually processed by paste extrusion. Its products include DuPont's well-known Teflon®. Prior experiments showed that fibrils of submicron dimensions are created among the PTFE particles during processing (see SEM micrographs below), possibly owing to the unwinding of crystallites. Since the concentration and property of these fibrils define the final strength the extrudate, we are conducting experiments and CFD simulations to explore the fibrillation mechanism and the rheological evolution of the paste. So far, we have developed a kinetic theory for the fibrillation process, and used shear-thinning/thickening and viscoelastic models for finite-element simulations. An analytical solution based on the radial flow hypothesis was also derived. These results will help us determine optimal processing conditions and die design.