Thermoplastic Processing of PTFE
Polytetrafluoroethylene (PTFE) withstands elevated temperatures, is chemical-resistant, light- and weather-resistant, has a very good friction characteristics, is non-adhesive, non-flammable and physiologically inert. However, because of the very high molecular weight, the viscosity is so high that until now it has been impossible to process the material as a thermoplastic. For this reason, PTFE components have been manufactured by means of special compression molding and sintering techniques.
Recently, though, modified PTFE materials that can be processed as thermoplastics have come onto the market. The structure of the semi-crystalline materials consists of plate-like crystallites and amorphous zones in between. For the material to achieve good mechanical properties, the crystallites must be interconnected by means of so-called bonding molecules. In this newly developed PTFE material, the plate-like crystallites (lamellae) are about 10 times smaller than what is typically found in standard PTFE. This means that relatively short molecular chains can function as bonding molecules. These short molecular chains mean that the polymer melt has a lower viscosity, meaning that the material can be processed as a thermoplastic, for example, by means of injection molding and extrusion, but also by means of thermoforming, blow molding or melt spinning. At the usual processing temperatures, however, the PTFE melt corrodes steel. Screws, barrels and tooling must thus be in fabricated from appropriate corrosion-resistant materials.
Compared to the methods used previously to process PTFE, thermoplastic processing offers several major advantages. Among these are short cycle times, greater freedom regarding part design and more reliable processing during production. It is furthermore possible to recycle production waste into new parts.