Tetrafluoroethylene fine powder resins

Pure tetrafluoroethylene monomer under ambient conditions is an odorless, colorless, tasteless gas with low toxicity. It may be polymerized by either suspension or emulsion techniques. Both procedures require use of high pressures in an autoclave in order to maintain the monomer in liquid form. These techniques produce chemically identical product, the first a granular resin, and the second a fine powder (Eq. 23.7). 

PTFE is produced by free-radical polymerization mechanism in an aqueous media via addition polymerization of tetrafluoroethylene in a batch process. The initiator for the polymerization is usually a water-soluble peroxide, such as ammonium persulfate or disuccinic peroxide. A redox catalyst is used for low temperature polymerization. PTFE is produced by suspension (or slurry) polymerization without a surfactant to obtain granular resins or with a perfluori-nated surfactant emulsion polymerization) to produce fine powder and dispersion products. Polymerization temperature and pressure usually range from 0 to 100°C and 0.7 to 3.5 MPa. 

Commercially, PTFE is produced from the monomer tetrafluoroethylene by two different polymerization techniques, namely, suspension and emulsion polymerization. These processes give two vastly different physical forms of chemically identical PTFE. While suspension polymerization produces granular PTFE resin, emulsion polymerization produces an aqueous PTFE dispersion and PTFE fine powders (after coagulating the dispersion). 

Polytetrafluoroethylene is the polymer resulting from the free radical polymerisation of tetrafluoroethylene CF2=CF2. The reaction is usually carried out in an aqueous emulsion which produces sub-micron particles of the polymer, or in a suspension which gives rise to particles of 100 xm or greater. The polymer is processed from various resin grades, which differ in fineness, by means of preforming followed by sintering as in powder metallurgy. 

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