fluoropolymer
A fluoropolymer is a fluorocarbon-based polymer with multiple carbon–fluorine bonds. It is characterized by a high resistance to solvents, acids, and bases. The best known fluoropolymer is polytetrafluoroethylene under the brand name "Teflon, ...
s. 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 som ...
s of
tetrafluoroethylene
Tetrafluoroethylene (TFE) is a fluorocarbon with the chemical formula . It is a colorless gas. Its structure is . It is used primarily in the industrial preparation of fluoropolymers. It is the simplest perfluorinated alkene.
It was first repor ...
(C2F4) and
perfluoroether Perfluoroethers are a class of organofluorine compound containing one or more ether functional group. In general these compounds are structurally analogous to the related hydrocarbon ethers, except for the distinctive properties of fluorocarbons.
...
s (C2F3ORf, where Rf is a perfluorinated group such as
trifluoromethyl
The trifluoromethyl group is a functional group that has the formula . The naming of is group is derived from the methyl group (which has the formula ), by replacing each hydrogen atom by a fluorine atom. Some common examples are trifluoromethane ...
(CF3)). The properties of these polymers are similar to those of
polytetrafluoroethylene
Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene, and has numerous applications because it is chemically inert. The commonly known brand name of PTFE-based composition is Teflon by Chemours, a corporate spin-of ...
(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 Single bond, singularly bonded to oxygen; thus . Denoted usually with apostrophe('). The range of alkoxy groups is vast, the simplest being methoxy (). An ethoxy group () is found in the ...
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 light scattering by particles, scattering of light. On a macroscopic scale ...
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 Plastic extrusio ...
(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 i ...
. 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
PFA is produced as a
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 som ...
of
tetrafluoroethylene
Tetrafluoroethylene (TFE) is a fluorocarbon with the chemical formula . It is a colorless gas. Its structure is . It is used primarily in the industrial preparation of fluoropolymers. It is the simplest perfluorinated alkene.
It was first repor ...
and a
perfluoroether Perfluoroethers are a class of organofluorine compound containing one or more ether functional group. In general these compounds are structurally analogous to the related hydrocarbon ethers, except for the distinctive properties of fluorocarbons.
...
, usually
perfluoro(methyl vinyl ether)
Perfluoro(methyl vinyl ether) is a perfluorinated compound used as a precursor to fluoropolymers. It is the simplest unsaturated perfluoroether.
Preparation
Preparation begins with hexafluoropropylene oxide (HFPO) and carbonyl fluoride over ...
. Preparation of the perfluoroether precursors is more complex than partially fluorinated vinyl ethers, which can be made from the reaction of
tetrafluoroethylene
Tetrafluoroethylene (TFE) is a fluorocarbon with the chemical formula . It is a colorless gas. Its structure is . It is used primarily in the industrial preparation of fluoropolymers. It is the simplest perfluorinated alkene.
It was first repor ...
with
alkoxide
In chemistry, an alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They are written as , where R is the organyl substituent. Alkoxides are strong bases and, whe ...
s:
:
However, the instability of α-
fluoroalcohol Fluoroalcohols are organofluorine compounds consisting of an alcohol functional group with at least one C-F bond. These compounds often have distinctive solvent properties.
Perfluoroalcohols
Most primary and secondary perfluoroalcohols are unsta ...
s makes preparation of most perfluoroalkoxides impractical. Instead, production of vinyl perfluoroethers can be achieved by
pyrolysis
Pyrolysis is a process involving the Bond cleavage, separation of covalent bonds in organic matter by thermal decomposition within an Chemically inert, inert environment without oxygen. Etymology
The word ''pyrolysis'' is coined from the Gree ...
of a perfluoro(2-alkoxy carboxylate) salt.
This reaction, called dehalocarbonylation, proceeds by the elimination of from the carboxylate, forming a
carbanion
In organic chemistry, a carbanion is an anion with a lone pair attached to a tervalent carbon atom. This gives the carbon atom a negative charge.
Formally, a carbanion is the conjugate base of a carbon acid:
:
where B stands for the base (chemist ...
intermediate that then undergoes elimination of
fluoride
Fluoride (). According to this source, is a possible pronunciation in British English. is an Inorganic chemistry, inorganic, Monatomic ion, monatomic Ion#Anions and cations, anion of fluorine, with the chemical formula (also written ), whose ...
to form the alkene. The vinyl ether can also be prepared directly from an
acyl fluoride
An acyl halide (also known as an acid halide) is a chemical compound derived from an oxoacid by replacing a hydroxyl group () with a halide group (, where X is a halogen).
In organic chemistry, the term typically refers to acyl halides of carbox ...
by using
sodium carbonate
Sodium carbonate (also known as washing soda, soda ash, sal soda, and soda crystals) is the inorganic compound with the formula and its various hydrates. All forms are white, odourless, water-soluble salts that yield alkaline solutions in water ...
:
:
Common trademarks include Teflon-PFA, Hostaflon-PFA and Chemfluor.
Chemours
The Chemours Company (, ) is an American chemical industry, chemical company that was founded in July 2015 as a Corporate spin-off, spin-off from DuPont. It has its corporate headquarters in Wilmington, Delaware, United States. Chemours is the m ...
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 and health risks
The monomers of such perfluoroalkoxy alkane polymers, in common with other
per- and polyfluoroalkyl substances
Per- and polyfluoroalkyl substances (also PFAS, PFASs, and informally referred to as "forever chemicals") are a group of synthetic organofluorine chemical compounds that have multiple fluorine atoms attached to an alkyl chain; there are 7 milli ...
, 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.
In 2023, the United States EPA ''proposed'' "the first (US national) standard to limit (PFAs) in drinking water;" albeit only six of >12,000 such chemicals were addressed.
At high temperatures or in a fire,
fluoroelastomer
A fluoroelastomer is a fluorocarbon-based synthetic rubber. Fluoroelastomers generally have wide chemical resistance.
Composition
Several compositions of fluoroelastomers exist including FKM (by ASTM D1418 standard, equivalent to FPM by ISO/DIN ...
s decompose and may release
hydrogen fluoride
Hydrogen fluoride (fluorane) is an Inorganic chemistry, inorganic compound with chemical formula . It is a very poisonous, colorless gas or liquid that dissolves in water to yield hydrofluoric acid. It is the principal industrial source of fluori ...
. Any residue must be handled using protective equipment.
See also
*
Fluoropolymer
A fluoropolymer is a fluorocarbon-based polymer with multiple carbon–fluorine bonds. It is characterized by a high resistance to solvents, acids, and bases. The best known fluoropolymer is polytetrafluoroethylene under the brand name "Teflon, ...
*
Perfluoroether Perfluoroethers are a class of organofluorine compound containing one or more ether functional group. In general these compounds are structurally analogous to the related hydrocarbon ethers, except for the distinctive properties of fluorocarbons.
...