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General
- The substitution of
fluorine for a hydrogen on a carbon-backbone macromolecule creates a
unique class of rubbers typically referred to as fluoroelastomers.
- FKM is the
designation for about 80% of fluorinated elastomers as defined in ASTM
D1418.
- Fluorinated
elastomers are perfluoro elastomers (FFKM) and tetrafluoro
ethylene/propylene rubbers (FEPM).
- FKM, is the largest
category (80+%) of fluoroelastomer.
- All FKM designated
elastomers contain vinylidene fluoride (VF2), a disubstituted monomer.
- FKM is defined as
Fluoro rubber of the polymethylene type that utilizes vinylidene
fluoride as a comonomer and have substituent fluoro, alkyl,
perfluoroalkyl or perfluoroalkoxy groups in the polymer chain, with or
without a curesite monomer.
Process
- Fluoroelastomers are
generally made in an emulsion polymerization process.
- Fluoro-monomers such
as HFP, VF2, and TFE are fed to a reactor under elevated temperature and
pressure along with surfactants and other additives.
- Once the
polymerization is complete the latex is removed, the polymer coagulated
and washed, and the polymer is dried and packaged for use.
- Thermal
hydrodehalogenation (THD) is a conversion technique where halons and
CFCs react with hydrogen or hydrogen donor molecules at high temperature
to form a mixture of hydrofluorocarbons (HFCs), hydrocarbons,
perfluorocarbons and mineral acids as products.
Application
- Fluoropolymers are
designed for high demanding applications in hostile environments. They
represent a high level choice in applications where chemical environment
and high temperatures are the dominating factors.
- Fluorohydrocarbon
elastomers (FKM) are routinely used as sealing devices for gas turbine
engines, auxiliary power units, air cycle machines, filters, integrated
drive generators, hydraulic servos and actuators.
- O-rings used in
fittings, connectors, valves, pumps, filters and oil reservoirs.
- Radial lip seals used
in pumps. T-seals used in high pressure fittings andconnectors
Market
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