Perfluoroalkoxy alkane

Perfluoroalkoxy alkanes (PFA) are fluoropolymers. They are copolymers of tetrafluoroethylene (C2F4) and perfluoroethers (C2F3ORf, where Rf is a perfluorinated group such as trifluoromethyl (CF3)). The properties of these polymers are similar to those of polytetrafluoroethylene (PTFE). Compared to PTFE, PFA have better anti-stick properties, higher chemical resistance on expense of a lesser scratch resistance.[2] Other than in PTFE, the alkoxy substituents allow the polymer to be melt-processed. [3] On a molecular level, PFA 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 and have improved flow, creep resistance, and thermal stability close to or exceeding PTFE.[4] Thus, PFA are preferred when extended service is required in hostile environments involving chemical, thermal, and mechanical stress. PFA offer high melt strength, stability at high processing temperatures, excellent crack and stress resistance, a low coefficient of friction.[1] Similarly advantaged processing properties are found in fluorinated ethylene propylene (FEP), the copolymer of tetrafluoroethylene and hexafluoropropylene.[5] However FEP is ten times less capable to withstand repeated bending without fracture than PFA.[1]

"Perfluoroalkoxy" redirects here. This article is about specific fluoropolymers; for the broader class of fluoropolymers to which they belong, see Perfluoroether.
PFA
Density[1] 2150 kg/m3
Flexural modulus(E) 586 MPa
Tensile strength(t) 24 MPa
Elongation at break 300%
Folding endurance No break
Notch test
Melting point 315 °C
Maximum operating temperature 260 °C
Water absorption (ASTM) <0.03 % after 24 hours
Dielectric constant (Dk) at 1MHz 2.1
Dissipation factor at 1MHz 0.0001
Arc resistance < 180 seconds
Resistivity at 50% R. H. > 1016 Ω m
Perfluoroalkoxy alkane polymers are used to fabricate tubes to handle aggressive chemicals.

Common trademarks include Teflon®-PFA, Hostaflon®-PFA, and Chemfluor®.[6]

Applications

PFA are commonly used as materials for piping and fittings for aggressive chemicals, as well as corrosion-resistant lining of vessels in the chemical-processing industry. Typical applications include the construction of gas scrubbers, reactors, containment vessels, and piping.[7] In coal-fired power plants, they are used as lining for 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.[8]

PFA are also used as inert materials for sampling equipment in analytical chemistry and for geochemical or environmental in situ studies on field site when it is particularly important to avoid chemical contamination of metallic ions at trace levels.

Precautions

At high temperatures or in a fire, fluoroelastomers decompose and may release hydrogen fluoride. Any residue must be handled using protective equipment.

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References
  1. "PTFE, FEP, and PFA Specifications". Boedeker Corp. 2007. Retrieved 2007-12-22.
  2. "PTFE, FEP, PFA". TechnoFinish GmbH & Co. KG. Retrieved 2019-06-22.
  3. "PFA - Perfluoralkoxy". Reichelt Chemietechnik. Retrieved 2019-06-22.
  4. "PFA Properties". Fluorotherm Polymers. 2018. Retrieved 2018-11-04.
  5. Siegemund, Günter; Schwertfeger, Werner; Feiring, Andrew; Smart, Bruce; Behr, Fred; Vogel, Herward; McKusick, Blaine (2002). "Fluorine Compounds, Organic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a11_349..
  6. "Glossary: PFA - Perfluoralkoxy". Reichelt Chemietechnik. Retrieved 2019-06-22.
  7. Dietrich Braun, Kunststofftechnik für Einsteiger, Hanser, München, 2003.
  8. H. Saechtling: Kunststoff Taschenbuch, Hanser Verlag, Wien 1995, ISBN 3-446-17855-4.
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