Perfluoroalkoxy

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PFA
Line diagram of the perfluoroalkoxy monomer
Density[1]2150 kg/m3
Flexural modulus(E)586 MPa
Tensile strength(t)24 MPa
Elongation @ break300%
Folding enduranceNo break
Notch test
Melting point305 °C
Maximum operating
   temperature260 °C
Water absorption (ASTM)<0.03 % after 24 hours
Dielectric constant (Dk)
   at 1MHz2.1
Dissipation factor
   at 1MHz0.0001
Arc resistance< 180 seconds
Resistivity at 50% R.H.> 1016 Ω m
PFA tubing is very common in chemical handling applications

Perfluoroalkoxy or PFA is a type of fluoropolymer with properties similar to polytetrafluoroethylene (PTFE). It differs from the PTFE resins in that it is melt-processable using conventional injection molding and screw extrusion techniques.

PFA was invented by DuPont and is sold under the brandname Teflon PFA. Teflon is better known as the trade name for PTFE. Other brandnames for granules are Neoflon PFA from Daikin or Hyflon PFA from Solvay Solexis.

PFA is very similar in composition to the fluoropolymers PTFE and FEP (fluorinated ethylene-propylene). PFA and FEP both share PTFE's useful properties of low coefficient of friction and non-reactivity, but are more easily formable. PFA is softer than PTFE and melts at 305 °C.

Another version of polytetrafluoroethylene perfluoro methylvinylether, with a different ratio of PTFE and MVE monomers from PFA, is MFA.

Properties

Useful comparison tables of PTFE against FEP, PFA and ETFE can be found on DuPonts website, listing the mechanical, thermal, chemical, electrical and vapour properties of each, side by side.[2]

PFA is similar to FEP in terms of its mechanical properties. These two are both superior to PTFE with regards to their flexibility, making them useful for tubing applications. However, their ability to endure repetitive folding (flex life) is actually lower than PTFEs own. PFA has a higher flex life than FEP.

PFA is preferable to FEP where heat is concerned, but PTFE itself is slightly more resistant to heat than both. PFA is more affected by water absorption and weathering than FEP, but is superior in terms of salt spray resistance.

Perhaps the most impressive feature of PFA is its electrical properties, as it features the dielectric constant of PTFE, and an almost identical dissipation factor, but a dielectric strength that is around four times higher.

ETFE is effectively a high strength engineering version of these three, and features what would likely be considered to be slightly degraded performance when compared with the other three.

Applications

Due to its flexibility, extreme resistance to chemical attack and optical transparency, this material, along with FEP is routinely used for plastic labware and tubing that involves critical or highly corrosive processes. Nalgene is a well known laboratory supplier that makes extensive use of the two materials.

Another application are sheet linings for chemical equipment where fabric backed PFA sheets (SYMALIT PFA). The use of a PFA liner allows to replace expensive metals and alloys like Inconel or Hastelloy with lined carbon steel or lined fibre-reinforced plastic (FRP). Examples are SYMALIT PFA lined columns, scrubbers, reactors and pipes which stand harsh environments like concentrated HF and HCl and halogens.

Notes