Perfluoroalkoxy alkanes (PFA) are
fluoropolymers. They are
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 of
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
2F
4) and
perfluoroethers (C
2F
3OR
f, where R
f is a perfluorinated group such as
trifluoromethyl
The trifluoromethyl group is a functional group that has the formula -CF3. The naming of is group is derived from the methyl group (which has the formula -CH3), by replacing each hydrogen atom by a fluorine atom. Some common examples are trifluoro ...
(CF
3)). The properties of these polymers are similar to those of
polytetrafluoroethylene (PTFE). Compared to PTFE, PFA has better anti-stick properties and higher chemical resistance, at the expense of lesser scratch resistance.
Properties
Unlike with PTFE, the
alkoxy
In chemistry, the alkoxy group is an alkyl group which is singularly bonded to oxygen; thus . The range of alkoxy groups is vast, the simplest being methoxy (). An ethoxy group () is found in the organic compound ethyl phenyl ether (, also ...
substituents allow the polymer to be melt-processed.
On a molecular level, PFA polymers have a smaller chain length and higher chain entanglement than other fluoropolymers. They also contain an oxygen atom at the branches. This results in materials that are more
translucent
In the field of optics, transparency (also called pellucidity or diaphaneity) is the physical property of allowing light to pass through the material without appreciable scattering of light. On a macroscopic scale (one in which the dimensions ...
and have improved flow and creep resistance, with thermal stability close to or exceeding PTFE.
Thus, PFA is preferred when extended service is required in hostile environments involving chemical, thermal, and mechanical stress. PFA offers high melt strength, stability at high processing temperatures, excellent crack and stress resistance and a low coefficient of friction.
Similarly enhanced processing properties are found in
fluorinated ethylene propylene
Fluorinated ethylene propylene (FEP) is a copolymer of hexafluoropropylene and tetrafluoroethylene. It differs from the polytetrafluoroethylene (PTFE) resins in that it is melt-processable using conventional injection molding and screw extrusion t ...
(FEP), the copolymer of tetrafluoroethylene 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 ...
. However FEP is ten times less capable of withstanding repeated bending without fracture than PFA.
Applications
PFA is commonly used as a material for piping and as fittings for aggressive chemicals, as well as the corrosion-resistant lining of vessels in the chemical-processing industry.
Typical applications include the construction of gas scrubbers, reactors, containment vessels and piping.
In coal-fired power plants, it is used for lining heat exchangers. By channeling crude gas through a PFA-lined apparatus, the gas stream can be cooled below its condensation temperature without damaging the heat exchanger. Its use contributes to increasing the efficiency of the whole plant.
PFA is also used to make sampling equipment in analytical chemistry and for geochemical or environmental ''in situ'' studies in the field, when it is particularly important to avoid chemical contamination from metallic ions at trace levels.
Production
Common trademarks include Teflon-PFA, Hostaflon-PFA and Chemfluor.
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 ...
claims to be the only U.S. producer of PFA at its Fayetteville Works plant in northern
Bladen County
Bladen County ()
, from the North Carolina Collection's website at the .
Environmental risks
The monomers of such Perfluoroalkoxy alkane polymers, in common with other
per- and polyfluoroalkyl substances
Per- and polyfluoroalkyl substances (PFASs) are synthetic organofluorine chemical compounds that have multiple fluorine atoms attached to an alkyl chain. An early definition, from 2011, required that they contain at least one perfluoroalkyl mo ...
, are widespread in the environment due to human production and release of the chemicals; so durable that they are referred to as "forever chemicals"; and have detrimental health concerns not yet fully understood.
At high temperatures or in a fire, fluoroelastomers decompose and may release
hydrogen fluoride. Any residue must be handled using protective equipment.
See also
*
Fluoropolymer
*
Perfluoroether
References
{{reflist
Fluoropolymers
Thermoplastics
Organofluorides