Fluorinated ethylene propylene or FEP is a copolymer of hexa fluoro propylene and tetra fluoro ethylene. It differs from the PTFE (poly tetra fluoro ethylene) resins in that it is melt-processible using conventional injection molding and screw extrusion techniques. Fluorinated ethylene propylene was invented by DuPont and is sold under the brand name Teflon® FEP. Other brand names are Neoflon® from Daikin or Dyneon® FEP from Dyneon/3M.
FEP is very similar in composition to the fluoro polymers PTFE (poly tetra fluoro ethylene) and PFA (perfluoro alkoxy 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.
Useful comparison tables of PTFE against FEP, PFA and ETFE can be found on DuPonts website, listing the mechanical, thermal, chemical, electrical and vapor properties of each, side by side.
In terms of corrosion resistace, FEP is the only other readily available fluoro polymer that can match PTFE's own resistance to caustic agents, as it is a pure carbon-fluorine structure and fully fluorinated.
Thermally, FEP stands out from PTFE and PFA by having a melting point of 260 °C (500 °F), around forty degrees lower than PFA and lower again than PTFE.
Electrically, PTFE, FEP and PFA have identical dielectric constants, but FEP's dielectric strength is only surpassed by PFA. However, whilst PFA has a similar dissipation factor to PTFE, FEP's dissipation is around six times that of PFA and EFTE (making it a more non-linear conductor of electrostatic fields).
Mechanically, FEP is slightly more flexible than PTFE. Perhaps surprisingly, it does not withstand repetitive folding as well as PTFE. It also features a poorer co-efficient of dynamic friction, is softer and has a slightly lower tensile strength than PTFE and FAP.
A noteworthy property of FEP is that it is vastly superior to PTFE in some coating applications involving exposure to detergents.
ETFE, in many ways, can be thought of as belonging to a different group, as it is essentially a high strength engineering version of the others featuring what are likely to be considered slightly diminished properties in the other fields when compared with PTFE, FEP and PFA.
Case History :
2.5mm FEP + MS agitator lining @ 150 Deg C for 80% Sulphuric acid with traces of mercury salt.