HOME

TheInfoList



OR:

FKM is a family of
fluorocarbon Fluorocarbons are chemical compounds with carbon-fluorine bonds. Compounds that contain many C-F bonds often has distinctive properties, e.g., enhanced stability, volatility, and hydrophobicity. Fluorocarbons and their derivatives are commerci ...
-based
fluoroelastomer {{refimprove, date=June 2008 A fluoroelastomer is a fluorocarbon-based synthetic rubber. Fluroelastomers generally have wide chemical resistance. Composition Several compositions of fluoroelastomers exist including FKM (by ASTM D1418 standard, equi ...
materials defined by
ASTM International ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, an ...
standard D1418, and ISO standard 1629. It is commonly called fluorine rubber or fluoro-rubber. FKM is an abreveation of Fluorine Kautschuk Material. All FKMs contain
vinylidene Methylidenecarbene (systematically named λ2-ethene and dihydrido-1κ2''H''-dicarbon(''C''—''C'')) is an organic compound with the chemical formula (also written [] or ). It is a metastability, metastable proton tautomer of acetylene, which on ...
fluoride as a monomer. Originally developed by DuPont (1802–2017), DuPont (under the brand name Viton, now owned by
Chemours Chemours (, ) is an American chemical company that was founded in July 2015 as a spin-off from DuPont. It has its corporate headquarters in Wilmington, Delaware, United States. History In October 2013, DuPont announced that it was planning to ...
), FKMs are today also produced by many companies, including:
Daikin is a Japanese multinational air conditioning manufacturing company headquartered in Osaka. It has operations in Japan, China, Australia, the United States, India, Southeast Asia, Europe, the Middle East, Latin America, and Africa. Daikin is th ...
(Dai-El), 3M (Dyneon),
Solvay S.A. Solvay is a Belgian multinational chemical company established in 1863, with its headquarters located in Neder-Over-Heembeek, Brussels, Belgium. In 2015, it realized €12.4 billion in revenues, €2.336 billion of EBITDA, 43% of its sales in ...
(Tecnoflon), HaloPolymer (Elaftor), Gujarat Fluorochemicals (Fluonox), and several Chinese manufacturers. Fluoroelastomers are more expensive than
neoprene Neoprene (also polychloroprene) is a family of synthetic rubbers that are produced by polymerization of chloroprene.Werner Obrecht, Jean-Pierre Lambert, Michael Happ, Christiane Oppenheimer-Stix, John Dunn and Ralf Krüger "Rubber, 4. Emulsion Ru ...
or
nitrile rubber Nitrile rubber, also known as nitrile butadiene rubber, NBR, Buna-N, and acrylonitrile butadiene rubber, is a synthetic rubber derived from acrylonitrile (ACN) and butadiene. Trade names include Perbunan, Nipol, Krynac and Europrene. This rubber i ...
elastomer An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus and high failure strain compared with other materials. The term, a portmanteau of ''elastic ...
s. They provide additional heat and chemical resistance. FKMs can be divided into different classes on the basis of either their chemical composition, their
fluorine Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists at standard conditions as a highly toxic, pale yellow diatomic gas. As the most electronegative reactive element, it is extremely reactiv ...
content, or their
cross-link In chemistry and biology a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural ...
ing mechanism.


Types

On the basis of their chemical composition FKMs can be divided into the following types: * Type-1 FKMs are composed of
vinylidene fluoride 1,1-Difluoroethylene, also known as vinylidene fluoride, is a hydrofluoroolefin. It is a flammable gas. Global production in 1999 was approximately 33,000 metric tons. It is primarily used in the production of fluoropolymers such as polyvinyliden ...
(VDF) and
hexafluoropropylene Hexafluoropropylene is the fluoroalkene with the formula CF3CF=CF2. It is the perfluorocarbon counterpart to the hydrocarbon propylene. It is mainly used to produce copolymers with tetrafluoroethylene. Hexafluoropropylene is used as a chemical i ...
(HFP).
Copolymer In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are some ...
s 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 Tetrafluoroethylene (TFE) is a fluorocarbon with the chemical formula C2 F4. It is the simplest perfluorinated alkene. This gaseous species is used primarily in the industrial preparation of fluoropolymers. Properties Tetrafluoroethylene is a c ...
(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
terpolymer In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are some ...
s. Typically, the fluorine content of type-3 FKMs ranges from 62 to 68 weight percent. * Type-4 FKMs are composed of
propylene Propylene, also known as propene, is an unsaturated organic compound with the chemical formula CH3CH=CH2. It has one double bond, and is the second simplest member of the alkene class of hydrocarbons. It is a colorless gas with a faint petrole ...
, TFE, and VDF. While base resistance is increased in type-4 FKMs, their swelling properties, especially in
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
s, 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 Ethylene ( IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene ...
. Known for base resistance and high-temperature resistance to hydrogen sulfide.


Cross-linking mechanisms

There are three established
cross-link In chemistry and biology a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural ...
ing mechanisms used in the curing process of FKMs. *
Diamine A diamine is an amine with exactly two amino groups. Diamines are used as monomers to prepare polyamides, polyimides, and polyureas. The term ''diamine'' refers mostly to primary diamines, as those are the most reactive. In terms of quantities ...
cross-linking using a blocked diamine. In the presence of basic (alkaline) media, VDF is vulnerable to dehydrofluorination, which enables the addition of the diamine to the polymer chain. Typically,
magnesium oxide Magnesium oxide ( Mg O), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2− ions ...
is used to neutralize the resulting
hydrofluoric acid Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water. Solutions of HF are colourless, acidic and highly corrosive. It is used to make most fluorine-containing compounds; examples include the commonly used pharmaceutical antidepress ...
and rearrange into
magnesium fluoride Magnesium fluoride is an inorganic compound with the formula MgF2. The compound is a white crystalline salt and is transparent over a wide range of wavelengths, with commercial uses in optics that are also used in space telescopes. It occurs natur ...
and water. Although rarely used today, diamine curing provides superior rubber-to-metal bonding properties as compared with other cross-linking mechanisms. The diamine's capability to be hydrated makes the diamine cross-link vulnerable in aqueous media. * Ionic cross-linking ( dihydroxy cross-linking) was the next step in curing FKMs. This is today the most common cross-linking chemistry used for FKMs. It provides superior heat resistance, improved hydrolytic stability and better compression set than diamine curing. In contrast to diamine curing, the ionic mechanism is not an addition mechanism but an aromatic
nucleophilic substitution In chemistry, a nucleophilic substitution is a class of chemical reactions in which an electron-rich chemical species (known as a nucleophile) replaces a functional group within another electron-deficient molecule (known as the electrophile). Th ...
. Dihydroxy
aromatic compound Aromatic compounds, also known as "mono- and polycyclic aromatic hydrocarbons", are organic compounds containing one or more aromatic rings. The parent member of aromatic compounds is benzene. The word "aromatic" originates from the past grouping ...
s are used as the cross-linking agent, and
quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...
phosphonium salt In polyatomic cations with the chemical formula (where R is a hydrogen or an alkyl, aryl, or halide group). These cations have tetrahedral structures. The salts are generally colorless or take the color of the anions. Types of phosphonium c ...
s are typically used to accelerate the curing process. *
Peroxide In chemistry, peroxides are a group of compounds with the structure , where R = any element. The group in a peroxide is called the peroxide group or peroxo group. The nomenclature is somewhat variable. The most common peroxide is hydrogen p ...
cross-linking was originally developed for type 3 FKMs containing PMVE as diamine and
bisphenol The bisphenols () are a group of chemical compounds related to diphenylmethane. Most are based on two hydroxyphenyl functional groups linked by a methylene bridge. Exceptions include bisphenol S, P, and M. "Bisphenol" is a common name; the letter ...
ic cross-linking systems can lead to cleavage in a polymer
backbone chain In polymer science, the polymer chain or simply backbone of a polymer is the main chain of a polymer. Polymers are often classified according to the elements in the main chains. The character of the backbone, i.e. its flexibility, determines the ...
containing PMVE. While diamine and bisphenolic cross-linking are ionic reactions, peroxide cross-linking is a
free-radical In chemistry, a radical, also known as a free radical, is an atom, molecule, or ion that has at least one unpaired valence electron. With some exceptions, these unpaired electrons make radicals highly chemically reactive. Many radicals spont ...
mechanism. Though peroxide cross-links are not as thermally stable as bisphenolic cross-links, they normally are the system of choice in aqueous media and nonaqueous
electrolyte An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dis ...
media.


Properties

Fluoroelastomers provide excellent high temperature (up to 500°F or 260°C) and aggressive fluids resistance when compared with other
elastomers An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus and high failure strain compared with other materials. The term, a portmanteau of ''elastic ...
, while combining the most effective stability to many sorts of chemicals and fluids such as oil, diesel,
ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a hyd ...
mix or body fluid. The performance of fluoroelastomers in aggressive chemicals depends on the nature of the base polymer and the compounding ingredients used for molding the final products (e.g.
o-rings An O-ring, also known as a packing or a toric joint, is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a round cross-section, designed to be seated in a groove and compressed during assembly between two or more par ...
). Some formulations are generally compatible with
hydrocarbons In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or e ...
, but incompatible with
ketones In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double bo ...
such as
acetone Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour. Acetone is miscible wi ...
and
methyl ethyl ketone Butanone, also known as methyl ethyl ketone (MEK), is an organic compound with the chemical formula, formula CH3C(O)CH2CH3. This colourless liquid ketone has a sharp, sweet odor reminiscent of acetone. It is produced industrially on a large scale, ...
,
ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides are f ...
solvents such as
ethyl acetate Ethyl acetate ( systematically ethyl ethanoate, commonly abbreviated EtOAc, ETAC or EA) is the organic compound with the formula , simplified to . This colorless liquid has a characteristic sweet smell (similar to pear drops) and is used in glues, ...
,
amines In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such ...
, and
organic acids An organic acid is an organic compound with acidic properties. The most common organic acids are the carboxylic acids, whose acidity is associated with their carboxyl group –COOH. Sulfonic acids, containing the group –SO2OH, are rel ...
such as
acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...
. They can be easily distinguished from many other elastomers because of their high
density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematicall ...
of over 1800 kg/m3, significantly higher than most types of rubber.


Applications

Because of their outstanding performance they find use in a number of sectors, including the following: * Chemical process and
petroleum refining An oil refinery or petroleum refinery is an industrial process plant where petroleum (crude oil) is transformed and refined into useful products such as gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, liquefie ...
, where they are used for seals, pumps, gaskets and so on, due to their resistance to chemicals; * Analysis and process instruments: separators, diaphragms, cylindrical fittings, hoops, gaskets, etc. *
Semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...
manufacturing; * Food and pharmaceutical, because of their low degradation, also in contact with fluids; *
Aviation Aviation includes the activities surrounding mechanical flight and the aircraft industry. ''Aircraft'' includes fixed-wing and rotary-wing types, morphable wings, wing-less lifting bodies, as well as lighter-than-air craft such as hot air ...
and
aerospace Aerospace is a term used to collectively refer to the atmosphere and outer space. Aerospace activity is very diverse, with a multitude of commercial, industrial and military applications. Aerospace engineering consists of aeronautics and astr ...
: high operating temperatures and high altitudes require superior heat and low-temperature resistance. They are suitable for the production of wearables, due to low wear and discoloration even during prolonged lifetimes in contact with skin oils and frequent exposure to light, while guaranteeing high comfort and stain resistance; The
automotive industry The automotive industry comprises a wide range of companies and organizations involved in the design, development, manufacturing, marketing, and selling of motor vehicles. It is one of the world's largest industries by revenue (from 16 % such ...
represents their main application sector, where constant reach for higher efficiencies push manufacturers towards high-performing materials. An example are FKM o-rings used as an upgrade to the original neoprene seals on Corvair pushrod tubes that deteriorated under the high heat produced by the engine, allowing oil leakage. FKM tubing or lined hoses are commonly recommended in automotive and other transportation fuel applications when high concentrations of biodiesel are required. Studies indicate that types B and F (FKM- GBL-S and FKM-GF-S) are more resistant to acidic biodiesel. (This is because biodiesel fuel is unstable and oxidizing.) FKM O-rings have been used safely for some time in
SCUBA diving Scuba diving is a mode of underwater diving whereby divers use breathing equipment that is completely independent of a surface air supply. The name "scuba", an acronym for "Self-Contained Underwater Breathing Apparatus", was coined by Chris ...
by divers using gas blends referred to as
nitrox Nitrox refers to any gas mixture composed (excepting trace gases) of nitrogen and oxygen. This includes atmospheric air, which is approximately 78% nitrogen, 21% oxygen, and 1% other gases, primarily argon. In the usual application, underwater ...
. FKMs are used because they have a lower probability of catching fire, even with the increased percentages of oxygen found in nitrox. They are also less susceptible to decay under increased oxygen conditions. While these materials have a wide range of applications, their cost is prohibitive when compared to other types of elastomers, meaning that their adoption must be justified by the need for outstanding performance (as in the aerospace sector) and is inadvisable for low-cost products. FKM/butyl gloves are highly impermeable to many strong organic solvents that would destroy or permeate commonly used gloves (such as those made with
nitrile In organic chemistry, a nitrile is any organic compound that has a functional group. The prefix '' cyano-'' is used interchangeably with the term ''nitrile'' in industrial literature. Nitriles are found in many useful compounds, including met ...
s).


Precautions

At high temperatures or in a fire, fluoroelastomers decompose and may release
hydrogen fluoride Hydrogen fluoride (fluorane) is an inorganic compound with the chemical formula . This colorless gas or liquid is the principal industrial source of fluorine, often as an aqueous solution called hydrofluoric acid. It is an important feedstock in ...
. Any residue must be handled using protective equipment.


See also

* Magnesium/Teflon/Viton


References

* * Overview of different types and their applications.


Weblinks


Properties of Elastomers - Chemical Resitancelist
(PDF; 0,6 MB)
Designing with Fluoroelastomers
(PDF; 0,8 MB)


See also

* FFKM, perfluoro-elastomers * FEPM, tetrafluoro ethylene/propylene elastomers {{DEFAULTSORT:FKM Organofluorides Elastomers Materials science Fluoropolymers