Rheology and processing of polytetrafluoroethylene (PTFE) paste

This is a review article on the paste extrusion of polytetrafluoroethylene (PTFE). The article begins with an overall presentation of the process. Important aspects related to this process are the physical properties of PTFE, its rheology, the morphological changes occurring during flow (fibrillation) that play a critical role on the dimensional stability of the final products, the geometrical characteristics, and types of dies used and temperature. PTFE is a compressible, zero Poisson's ratio material, and the mechanical properties of extrudates after extrusion are also discussed in view of fibrillation and Poisson's ratio.