Poly(ethylene trifluoride chloride)
Kel-F 300; Kel-F 81
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Polychlorotrifluoroethylene (PCTFE or PTFCE) is a thermoplastic chlorofluoropolymer with the molecular formula (CF2CClF)n, where n is the number of monomer units in the polymer molecule. It is similar to polytetrafluoroethene (PTFE), except that it is a homopolymer of the monomer chlorotrifluoroethylene (CTFE) instead of tetrafluoroethene. It has the lowest water vapor transmission rate of any plastic.
After World War II, PCTFE was commercialized under the trade name of Kel-F 81 by M W Kellogg company in early 1950s. The name "Kel-F" was derived from "Kellogg" and "fluoropolymer", which also represents other fluoropolymers like the copolymer poly(chlorotrifluoroethylene-co-vinylidene fluoride) (Kel-F 800). These were acquired by 3M Company in 1957. But 3M discontinued manufacturing of Kel-F by 1996.
PCTFE resin is now manufactured in different trade names such as Neoflon PCTFE from Daikin or Aclon from Allied Signal. However, Kel-F remains the most commonly used trade name still today. PCTFE films are sold under the tradename Aclar by Allied Signal. Tradenames of PCTFE in other manufacturing companies include Hostaflon C2 from Hoechst, Fluon from ICI, Voltalef from Arkema, Aclar from Honeywell, Plaskon from Allied Chemical Corporation and Halon from Ausimont USA.
PCTFE is an addition homopolymer. It is prepared by the free-radical polymerization of chlorotrifluoroethylene (CTFE) and can be carried out by solution, bulk, suspension and emulsion polymerization.
PCTFE has high tensile strength and good thermal characteristics. It is nonflammable and the heat resistance is up to 175 °C. It has a low coefficient of thermal expansion. The glass transition temperature (Tg) is around 45 °C.
The presence of a chlorine atom, having greater atomic radius than that of fluorine, hinders the close packing possible in PCTFE. This results in having a relatively lower melting point among fluoropolymers, around 210–215 °C.
PCTFE is resistant to the attack by most chemicals and oxidizing agents, a property exhibited due to the presence of high fluorine content. However, it swells slightly in halocarbon compounds, ethers, esters and aromatic solvents. PCTFE is resistant to oxidation because it does not have any hydrogen atoms.
Differences from PTFE
PCTFE is a homopolymer of chlorotrifluoroethylene (CTFE), whereas PTFE is a homopolymer of tetrafluoroethylene. The monomers of the former differs from that of latter structurally by having a chlorine atom replacing one of the fluorine atoms. Hence each repeating unit of PCTFE have a chlorine atom in place of a fluorine atom. This accounts for PCTFE to have less flexibility of chain and hence higher glass transition temperature. PTFE has a higher melting point and is more crystalline than PCTFE, but the latter is stronger and stiffer. Though PCTFE has excellent chemical resistance, it is still less than that of PTFE. PCTFE has lower viscosity, higher tensile strength and creep resistance than PTFE.
PCTFE finds majority of its application due to two main properties: water repulsion and chemical stability. PCTFE films are used as a protective layer against moisture. These include:
- moisture barrier in pharmaceutical blister packaging,
- water-vapour barrier for protecting phosphor coatings in electroluminescent lamps (the phosphor chemicals are sensitive to moisture),
- protection of liquid-crystal display (LCD) panels, which are sensitive to moisture.
Due to its chemical stability, it acts as a protective barrier against chemicals. It is used as a coating and prefabricated liner for chemical applications. PCTFE is also used for laminating other polymers like PVC, polypropylene, PETG, APET etc. It is also used in transparent eyeglasses, tubes, valves, chemical tank liners, O-rings, seals and gaskets.
PCTFE is used to protect sensitive electronic components because of its excellent electrical resistance and water repulsion. Other uses include flexible printed circuits and insulation of wires and cables.
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