Perfluoroalkoxy polymers

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General structure of perfluoroalkoxy polymers

Perfluoroalkoxy polymers (abbreviation PFA ) are completely fluorinated plastics, copolymers of tetrafluoroethylene (TFE) and perfluoroalkoxy vinyl ethers, such as. B. perfluorovinyl propyl ether .

They are a further development of the popular sintered material polytetrafluoroethylene (PTFE) and, like this, were first brought onto the market by DuPont . In contrast to PTFE, PFA can be processed thermoplastically ( injection molding , extrusion , welding ). Compared to PTFE (Teflon ® ), PFA have better non-stick properties, higher chemical resistance, but lower scratch resistance.

Brand names are Teflon ® -PFA, Dyneon ® -PFA, Hyflon ® -PFA and Chemfluor ® -PFA., Amboflon ® -PFA.

properties

PFA is poor in strength and hardness . It is resistant to almost all chemicals, has a very high temperature resistance and is flame-retardant ( UL94 V-0). PFA has a low coefficient of friction , largely inert behavior, high sliding wear and extremely low adhesion .

  • Usual processing temperatures: 380 ° C to 450 ° C
  • Melting point: approx. 310 ° C
  • Operating temperature: −200 ° C to +260 ° C
  • Coefficient of friction dyn dry: approx. 0.20-0.30
  • pronounced anti-adhesive behavior
  • low water absorption (<0.03%)
  • low thermal conductivity
  • typical density : approx. 2.15 g / cm³

use

PFA is used in trace element analysis to lower detection limits . The use of PFA vessel materials is ideally suited for this. Today trace elements analysis is carried out in concentrations in the ng / g ( ppb ) and pg / g (ppt) range. Vessel materials made of glass , quartz , polyethylene (PE) and polypropylene (PP) can cause concentration changes due to interactions between the vessel wall and the sample or reference solution and thus falsify analysis results.

Studies have shown that the shelf life of low-concentration element standards in vessels made of PFA is guaranteed for a very long time. The use of vessels made of PFA is therefore not only safer from an analytical point of view, but also more economical thanks to the rationalization of laboratory processes.

In addition to being used as a hose and fitting material for aggressive chemicals, PFA is commonly used as a corrosion-resistant lining in chemical plant construction. By lining components made of unalloyed steel or GRP , it offers an alternative to nickel-based materials such as Hastelloy , Inconel or Monel . Typical applications in chemical plant construction are gas washers , reactors, containers, pipes and centrifuges. Gas scrubbers lined with PFA are usually resistant to halogens .

It is found in coal-fired power plants as a lining for heat exchangers . The acid-resistant PFA allows raw gas flows to be cooled below the condensation point without damaging the heat exchanger. This can increase the efficiency of a power plant.

Further names are perfluoroalkoxy copolymer, perfluoroalkoxy polymer and perfluoroalkoxy copolymer.

Individual evidence

  1. Entry on perfluoroalkoxy polymers. In: Römpp Online . Georg Thieme Verlag, accessed on May 2, 2014.
  2. ^ Dietrich Braun, Kunststofftechnik für Einsteiger , Hanser, Munich, 2003. online
  3. a b Glossary: PFA - Perfluoroalkoxy. In: Reichelt Chemietechnik. Retrieved May 30, 2019 .
  4. Coatings: PTFE, FEP, PFA. In: TechnoFinish GmbH & Co. KG. Retrieved May 30, 2019 .

literature