FKM

FKM is a family of fluorocarbon-based fluoroelastomer materials defined by ASTM International standard D1418, and ISO standard 1629. It is commonly called fluorine rubber or fluoro-rubber. FKM is an abbreviation of Fluorine Kautschuk Material. All FKMs contain vinylidene fluoride as a monomer. Originally developed by DuPont (under the brand name Viton, now owned by Chemours), FKMs are today also produced by many companies, including: Daikin (Dai-El), 3M (Dyneon), Solvay S.A. (Tecnoflon), HaloPolymer (Elaftor), Gujarat Fluorochemicals (Fluonox), and several Chinese manufacturers. Fluoroelastomers are more expensive than neoprene or nitrile rubber elastomers. They provide additional heat and chemical resistance. FKMs can be divided into different classes on the basis of either their chemical composition, their fluorine content, or their cross-linking mechanism. On the basis of their chemical composition FKMs can be divided into the following types: Type-1 FKMs are composed of vinylidene fluoride (VDF) and hexafluoropropylene (HFP). Copolymers are the standard type of FKMs showing a good overall performance. Their fluorine content is approximately 66 weight percent. Type-2 FKMs are composed of VDF, HFP, and tetrafluoroethylene (TFE). Terpolymers have a higher fluorine content compared to copolymers (typically between 68 and 69 weight percent fluorine), which results in better chemical and heat resistance. Compression set and low temperature flexibility may be affected negatively. Type-3 FKMs are composed of VDF, TFE, and perfluoromethylvinylether (PMVE). The addition of PMVE provides better low temperature flexibility compared to copolymers and terpolymers. Typically, the fluorine content of type-3 FKMs ranges from 62 to 68 weight percent. Type-4 FKMs are composed of propylene, TFE, and VDF. While base resistance is increased in type-4 FKMs, their swelling properties, especially in hydrocarbons, are worsened. Typically, they have a fluorine content of about 67 weight percent. Type-5 FKMs are composed of VDF, HFP, TFE, PMVE, and ethylene.