PTFE and Fluoropolymers

Materials ·

Polytetrafluoroethylene (PTFE, Teflon) and related fluoropolymers (PFA, FEP, ECTFE) are used as linings, diaphragms, check valves, and shaft seals in pumps handling virtually any corrosive chemical, including hydrofluoric acid, fuming nitric acid, strong oxidizers, and aggressive solvents that attack all metals and most other polymers.

History

PTFE was accidentally discovered by Roy Plunkett at DuPont on 6 April 1938 in Jackson Laboratory, New Jersey, USA. Plunkett was working with tetrafluoroethylene refrigerant when polymerization produced a waxy solid with extraordinary non-stick and chemical resistance properties. DuPont patented PTFE and commercialized it as Teflon in 1945. The first PTFE-lined pump diaphragms appeared in the 1950s in chemical and pharmaceutical plants in the USA and Germany. PFA (perfluoroalkoxy) was introduced by DuPont in 1972 as a melt-processable alternative to PTFE with better purity for semiconductor use.

Key Properties

  • Density: 2.14 to 2.20 g/cm3 (PTFE); 2.12 to 2.17 g/cm3 (PFA)
  • Service temperature: -200 to +260 degrees C for both PTFE and PFA
  • Coefficient of friction: 0.05 to 0.10 — lowest of any solid polymer
  • Dielectric constant: 2.1 — excellent electrical insulator
  • PTFE requires sintering for manufacture; PFA and FEP are melt-processable by injection molding
  • Zero moisture absorption — properties constant at all humidity levels

Corrosion and Chemical Resistance

  • Resistant to virtually all inorganic and organic acids, bases, and solvents at any concentration
  • Including: hydrofluoric acid, aqua regia, fuming nitric acid, chlorosulfuric acid, sodium hydroxide, and all halogenated solvents
  • Not attacked by any known chemical below 260 degrees C under pump service conditions
  • Only attacked by: molten alkali metals (sodium, potassium) and fluorine gas at elevated temperature
  • PTFE is the most chemically inert solid polymer known to materials science
  • Permeation by aggressive chemicals possible through thin-section linings — design minimum 3 mm wall thickness

Grades and Standards

  • Virgin PTFE: ASTM D1457 types I to V; semiconductor grade: ASTM D4895
  • PFA (perfluoroalkoxy): DuPont Teflon PFA, Daikin Neoflon PFA
  • FEP (fluorinated ethylene propylene): DuPont Teflon FEP for lining applications
  • ECTFE (ethylene chlorotrifluoroethylene): Halar by Solvay for pump lining
  • SEMI F57 covers purity testing for semiconductor-grade fluoropolymer wetted components
  • USP Class VI certification available for pharmaceutical contact pump applications

Applications

  • Diaphragms in AODD pumps handling hydrofluoric acid and fuming acids
  • Lined pump casings for sulfuric acid concentration service
  • Shaft seal and packing rings in corrosive chemical process pumps
  • Ball check valves in metering pumps for strong oxidizing chemicals
  • PTFE-lined peristaltic pump tubing for concentrated acids in laboratory environments
  • Semiconductor wet bench recirculation pump linings using PFA
  • Pharmaceutical API synthesis transfer pumps with USP Class VI certification

Advantages

  • Unmatched chemical resistance — no other solid material is more chemically inert
  • Extremely wide operating temperature range (-200 to +260 degrees C)
  • Excellent release properties — product buildup does not adhere to contact surfaces
  • FDA and USP Class VI approved grades available for food and pharma contact
  • Zero contamination of ultra-pure process liquids — no ion extraction or leaching

Limitations

  • PTFE cannot be injection-molded — high manufacturing cost for complex shapes
  • Cold flow (creep) under sustained mechanical load — requires metal backup rings
  • Poor abrasion resistance — unsuitable for slurry service environments
  • Permeation by aggressive chemicals possible through thin-section linings
  • PFA and FEP are much more expensive than PP or PVDF per kilogram of material
  • PTFE bonding to metal substrates requires mechanical attachment rather than adhesive joining

Selection Criteria

  • Use PTFE diaphragms in all AODD pumps handling acids above 10 percent concentration
  • Specify PFA lining for ultra-pure semiconductor process chemical pump wetted paths
  • Use PTFE packing for shaft seals in corrosive chemical centrifugal pumps as alternative to mechanical seals
  • Require Virgin PTFE (ASTM D1457 Type I) — never reprocessed PTFE — for high-purity applications
  • For structural pump casings pair PTFE lining with iron or steel outer body — PTFE alone is insufficient for pressure containment

Top 10 Manufacturers

  • 1. Chemours Company (USA) — ~25% of fluoropolymer pump material market; Teflon PTFE and PFA resins
  • 2. Daikin Industries Ltd. (Japan) — ~18%; Neoflon PTFE, PFA, and FEP resins for pump component manufacture
  • 3. Solvay S.A. (Belgium) — ~12%; Halar ECTFE and Solef PVDF for lined pump systems
  • 4. Saint-Gobain Performance Plastics (France) — ~8%; PTFE-lined pump casings and diaphragm assemblies
  • 5. Garlock Sealing Technologies (USA) — ~6%; filled PTFE sheet for pump diaphragm and seal applications
  • 6. White Knight Fluid Handling (USA) — ~5%; ultra-pure PFA pump bodies for semiconductor wet process tools
  • 7. DEPA GmbH (Germany) — ~5%; PTFE-lined AODD pumps for chemical and pharmaceutical service
  • 8. FLUX Geraete GmbH (Germany) — ~4%; PTFE-lined drum and container pumps for corrosive chemicals
  • 9. Yamada Corporation (Japan) — ~4%; PTFE diaphragm AODD pumps for chemical process service
  • 10. Alfluid (France) — ~3%; PFA centrifugal pumps for semiconductor and pharmaceutical ultra-pure applications