ASTM D1418, ISO 1629 Designation: FEPM
ASTM D2000, SAE J200 Type/Class: HK
Standard Color: Black
- Aflas® (Asahi Glass)
- Dyneon BRF® (Dyneon)
Relative Cost: High
General Temperature Range: 0° to +450° F
As a copolymer of tetrafluoroethylene (TFE) and propylene (P), TFE/P provides a unique combination of chemical, heat, and electrical resistance. Chemically, TFE/P resists both acids and bases, as well as steam, amine-based corrosion inhibitors, hydraulic fluids, alcohol, and petroleum fluids. TFE/P is also resistant to ozone and weather. TFE/P typically retains its remarkable chemical resistance even in high temperatures (up to 450° F / 232° C), and tests have shown that electrical resistance actually improves with heat exposure. Nor do physical properties suffer; tensile strength typically approaches 2,500 psi.
The first TFE/P compound to be commercially marketed was Aflas. In a sense, Aflas defined the initial boundaries for base-resistant materials. There are varying grades of Aflas, each with their own molecular weight. Most molded and extruded products are made from Aflas 150P, which has a molecular weight of about 130,000. In comparison, Aflas 100H has a molecular weight of 200,000 and is typically used where high pressures are to be sealed, such as in oil field applications. TFE/P compounds are also widely used in the chemical processing, automotive, and aerospace industries.
Though it was the first, Aflas is not the only base-resistant fluoroelastomer on the market. On the contrary, DuPont Dow offers a wide range of excellent materials in this area. Despite being marketed under the same trade name (Viton®) as their FKM "cousins," these base-resistant types more closely resemble FEPM formulations. Viton VTR-7480 is a copolymer of tetrafluoroethylene and propylene. Its chemical and processing properties are analogous to those of Aflas 150P, making Viton VTR-7480 suitable for both molded and extruded goods. Viton VTR-7512 is also a TFE/P copolymer, in this case similar to Aflas 100H. Because of its increased molecular weight (relative to Viton VTR-7480), Viton VTR-7512 is more extrusion resistant and therefore good at handling higher pressures.
DuPont’s engineers continue to develop new compounds in response to the ever-changing needs of industry. For example, automotive powertrain applications are making greater and greater demands on seal compounds. Increasingly aggressive lubricants and higher temperatures are testing the limits of even the best materials. In response, DuPont developed two new base-resistant Viton materials. The first of these, Viton TBR-501C, is a terpolymer combining TFE/P with a low level of VF2. The "TBR" in the name refers to its "total base resistance." It is completely resistant to highly basic lubricant additives. Viton TBR-501C also has excellent high temperature resistance and outstanding processing characteristics.
The other new addition, Viton IBR-401C, is a terpolymer combining TFE/P with a higher level of VF2 (roughly three times as much as is in Viton TBR-501C). The "IBR" refers to its "intermediate base resistance." In other words, it is not as base-resistant as Viton TBR-501C, but it still offers a good balance of base and hydrocarbon resistance, as well as excellent processibility.
In both the IBR and the TBR types, presence of the VF2 does three things. First, it improves the low temperature properties of the materials. Second, it also improves the materials’ resistance to swelling in hydrocarbon oils, though this improvement comes at the expense of base resistance. That’s why Viton IBR-401C has less base resistance than Viton TBR-501C; the IBR material has a greater VF2 content. And third, the VF2 allows both these materials to be bisphenol cured rather than peroxide cured (which is the norm for TFE/P copolymers). Bisphenol curing makes for easier processing and lower scrap rates.
FEPM performs well in:
- Numerous acids and alkalies
- Amines (anti-freeze)
- Brake fluids
- Petroleum fluids
- Phosphate esters
FEPM does not perform well in:
- Acetic acid
FEPM undergoes substantial swell after immersion in solvents like acetone, chloroform, and trichlorotrifluoroethane. Notable compression set may rule FEPM out for some applications