PTFE, FEP, PVDF, PFA, ETFE, PCTFE, ECTFE and PVF
In general, the fluoroplastic family offers plastics with chemical resistance, low and high temperature capability, resistance to weathering, low friction properties, electrical and thermal insulation and "slipperiness." We must remember, though, that none of the fluoroplastics can be readily joined by gluing or solvent cementing. Also, all of the fluoroplastics will burn when exposed to flame. But they will not continue to burn when the flame is removed.
PTFE (polytetrafluoroethylene) was the first fluorocarbon. It is the most chemically resistant plastic known. Only a few chemicals react with it. Its mechanical properties are low compared to other engineering plastics, but its properties remain at a useful level over a great temperature range (-400° to 500°F). Mechanical properties can be improved by the addition of fillers such as glass fiber, carbon, graphite, molybdenum disulfide and bronze. PTFE has excellent thermal and electrical insulation properties. And it has a low coefficient of friction. It is difficult to make anything adhere to PTFE. A material may stick to it, but the material can be peeled off or rubbed off. PTFE is not melt processible. It cannot be injection or blow molded, extruded by conventional means, nor vacuum formed. The resin must be compressed, then sintered (a controlled heat treatment) to produce a useful plastic.
FEP (fluorinated ethylene propylene) processes by conventional means. It is extruded and injection molded. It has the chemical resistance, mechanical and electrical properties of PTFE but a more narrow temperature range - maximum temperature is 400°F. A plastic converter can apply knit fiberglass to one side of an FEP sheet. Fabricators can weld glass backed sheets together over cylindrical molds and vessel closure molds (flat or dishod or conical heads). They then overwrap this "liner" with fiberglass reinforced thermoset resin to make chemical resistant tanks, vessels and columns for the corrosive chemical industry.
PVDF (poly-vinylidene fluoride) is a melt processible fluoropolymer capable of being injection and compression molded and screw extruded. It is stiffer and resists cold flow better than PTFE, FEP and PFA. However, its chemical resistance, antistick properties, lubricity, electrical properties and useful temperature range (-80° to 300°F) are lower than PTFE, FEP and PFA. Glass backed sheets of PVDF make liners for vessels as does FEP. Pipe and fittings of PVDF are one of the most economical and chemical resistant, high temperature solid pipe systems available.
PFA (perfluoroalkoxy) is also melt processible. Its properties are those of PTFE and include resistance to practically all chemicals, the useful temperature range of PTFE, resistance to weathering, low friction coefficient and excellent electrical insulation characteristics. It is, however, more expensive than PTFE and FEP resins.
ETFE (ethylenetetrafluoroethylene) is a copolymer of ethylene and tetrafluoroethylene and is readily processed by conventional methods. It has good thermal properties (maximum service temperature of 300°F) and abrasion resistance. It has greater strength and stiffness than PTFE, FEP and PFA and has excellent impact strength.
PCTFE (polychlorotrifluoroethylene) is melt processible. Within its service temperature range, it has greater tensile and compressive strength than PTFE, FEP or PFA. At high temperatures it is subject to stress cracking. It does not have the solvent resistance of PTFE, FEP, PFA or ETFE. However, its radiation resistance is better.
ECTFE (ethylene-chlorotrifluoroethylene) is a copolymer of ethylene and PCTFE. It is melt processible. It has excellent electric insulating properties. At ambient temperatures its mechanical properties compare to those of nylon 6. It has excellent impact resistance at ambient and sub ambient temperatures. Glass backed sheets of ECTFE make liners for vessels like FEP and PVDF. Its service temperature ranges from -80° to 300°F.
PVF (polyvinyl fluoride) has outstanding resistance to weathering and good resistance to abrasion and staining. It is used as a surfacing film for industrial, architectural and decorative building materials.