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FKMFrom Wikipedia, the free encyclopedia

FKM(FPM by ISO) is the designation for about 80% of fluoroelastomers as defined in ASTM D1418. Other

fluorinated elastomers areperfluoro-elastomers(FFKM) and tetrafluoro ethylene/propylene rubbers

(FEPM). All FKMs contain vinylidene fluoride as a monomer. Originally developed by DuPont (Viton), FKMs

are today also produced by Daikin Chemical (Dai-El), 3M's Dyneon (Dyneon Fluoroelastomers), Solvay

Specialty Polymers (Tecnoflon) and HaloPolymer (Elaftor). 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

crosslinking mechanism.

Contents

1 Types

1.1 FFKM

2 Crosslinking mechanisms

3 References

4 External links

Types

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 typically

ranges around 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

affectednegatively.

Type 3 FKMsare composed of VDF, HFP, TFE, perfluoromethylvinylether (PMVE). The addition of

PMVE provides better low temperature flexibility compared to copolymers and terpolymers. Typicallythe fluorine contentof 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. Type 5 FKM is known for

base resistance and high temperature hydrogen sulfide resistance.[1]

FFKM

FFKMs are perfluoroelastomeric materials. They have excellent resistance to high temperatures[2]and

chemicals. Certain grades have a maximum continuous service temperature of 327 C (621 F). They are

commonly used to make O-rings and gaskets that are used in applications that involve contact with

hydrocarbons or highly corrosive fluids, or when a wide range of temperatures are encountered.

http://en.wikipedia.org/wiki/Hydrogen_sulfidehttp://en.wikipedia.org/wiki/Ethylenehttp://en.wikipedia.org/wiki/Neoprenehttp://en.wikipedia.org/wiki/Nitrile_rubberhttp://en.wikipedia.org/w/index.php?title=Tecnoflon&action=edit&redlink=1http://en.wikipedia.org/wiki/DuPonthttp://en.wikipedia.org/wiki/Vitonhttp://en.wikipedia.org/wiki/Fluorocarbonhttp://en.wikipedia.org/wiki/Fluoroelastomerhttp://en.wikipedia.org/wiki/ASTMhttp://en.wikipedia.org/wiki/Hydrogen_sulfidehttp://en.wikipedia.org/wiki/Ethylenehttp://en.wikipedia.org/wiki/Propylenehttp://en.wikipedia.org/wiki/Tetrafluoroethylenehttp://en.wikipedia.org/wiki/Hexafluoropropylenehttp://en.wikipedia.org/wiki/VDFhttp://en.wikipedia.org/wiki/Nitrile_rubberhttp://en.wikipedia.org/wiki/Neoprenehttp://en.wikipedia.org/w/index.php?title=Tecnoflon&action=edit&redlink=1http://en.wikipedia.org/wiki/Solvay_(company)http://en.wikipedia.org/wiki/3Mhttp://en.wikipedia.org/wiki/Daikinhttp://en.wikipedia.org/wiki/Vitonhttp://en.wikipedia.org/wiki/DuPonthttp://en.wikipedia.org/wiki/Fluorocarbonhttp://en.wikipedia.org/wiki/ASTMhttp://en.wikipedia.org/wiki/Fluoroelastomer

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Crosslinking mechanisms

There are three established crosslinking mechanisms used in the curing process of FKMs.

Diamine crosslinking using a blocked diamine. In the presence of basic media VDF is vulnerable to

dehydrofluorination which enables the addition of the diamine to the polymer chain. Typically magnesium

oxide is used to catch the resulting hydrofluoric acid and rearrange into magnesium fluoride and water.

Although rarely used today, diamine curing provides superior rubber-to-metal bonding properties ascompared with other crosslinking mechanisms. The diamine's capability to be hydrated makes the diamine

crosslink vulnerable in aqueous media.

Ioniccrosslinking (dihydroxy crosslinking) was the next step in curing FKMs. This is the most common

crosslinking chemistry used for FKMs. It provides superior heat resistance, improved hydrolytic stability

andbetter compression set than diamine curing. In contrast to diamine curing the ionic mechanism is not

an addition mechanism but an aromatic nucleophilic substitution. Dihydroxy aromatic compounds are

usedas the crosslinking agent and quaternary phosphonium salts are typically used to accelerate the

curing process.

Peroxide crosslinking was originally developed for type 3 FKMs containing PMVE as diamine andbisphenolic crosslinking systems can lead to cleavage in a polymer backbone containing PMVE. While

diamine and bisphenolic crosslinking are ionic reactions, peroxide crosslinking is a free radical

mechanism. Though peroxide crosslinks are not as thermally stable as bisphenolic crosslinks, they

normally are the system of choice in aqueous and nonaqueous electrolytes.

References

1. ^http://www.swjagels.com/uploads/Base_Resistant_FKM_Technology_in_Oilfield_Seals.pdf

2. ^E. I. DuPont, Kalrez Product Brochure.

External links

Designing with Fluoroelastomers (http://www.zrunek.at/viton-fkm-fpm-

fluorelastomere/download/zruelast-fpm-designing-with-fluoroelastomers.pdf)

Fluorine-Containing Elastomers (http://www.sealseastern.com/PDF/FluoroAcsChapter.pdf)

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Categories: Organofluorides Elastomers Materials science

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