Paste Extrusion of Polytetrafluoroethylene: Temperature, Blending and Processing Aid Effects

Abstract

Abstract Blends of different PTFE fine powder resins have been prepared and extruded in an attempt of improving the PTFE paste extrusion process and/or the extrudates. The extrusion pressure and the mechanical properties of the extrudates were found to fall between those exhibited by the pure components. While this is an expectable behavior, it offers opportunities for controlling the degree of fibrillation needed in the final products by mixing highly fibrillated with low fibrillated PTFE resins. Boron nitride and organically modified montmorillonite clays (solid lubricants) are also tested as additives to the lubricants used in the PTFE paste extrusion in order to identify enhanced processing aids. It was found that the addition of boron nitride and clays increase the extrusion pressure but at the same time improve the mechanical properties of the final extrudates in most cases. This again offers possibilities for controlling the final mechanical properties by controlling the degree of fibrillation, i. e., by adding a small amount of solid lubricants to adjust pressure, fibrillation, and thus the final mechanical properties. Finally, it is shown that fibrillation depends on temperature. Moreover, the mechanical properties of extrudates increase as the temperature goes through its two transition temperatures of 19 °C and 30 °C that render PTFE particles more deformable and prone to fibrillation.