Fluorinated ethylene propylene

Fluorinated ethylene propylene or FEP is a copolymer of hexafluoropropylene and tetrafluoroethylene. It differs from the PTFE (polytetrafluoroethylene) resins in that it is melt-processable using conventional injection molding and screw extrusion techniques. Fluorinated ethylene propylene was invented by DuPont and is sold under the brandname Teflon FEP. Other brandnames are Neoflon FEP from Daikin or Dyneon FEP from Dyneon/3M.

FEP is very similar in composition to the fluoropolymers PTFE (polytetrafluoroethylene) and PFA (perfluoroalkoxy polymer resin). FEP and PFA both share PTFE's useful properties of low friction and non-reactivity, but are more easily formable. FEP is softer than PTFE and melts at 260 °C; it is highly transparent and resistant to sunlight.

FEP is produced by free-radical polymerization of mixtures of tetrafluoroethylene and hexafluoropropylene. The mixture is biased to compensate for the relatively low reactivity of the propylene component. The process is typically initiated with peroxydisulfate, which homolyzes to generate sulfate radicals. Because FEP is poorly soluble in almost all solvents, the polymerization is conducted as an emulsion in water, often using a surfactant such as PFOS. The polymer contains about 5% of the propylene component.

Useful comparison tables of PTFE against FEP, PFA and ETFE can be found on DuPont's website, listing the mechanical, thermal, chemical, electrical and vapour properties of each, side by side.

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