Tetrafluoroethylene aqueous dispersions

Chemically, THV Fluoroplastic (hereafter referred to as THV) is a terpolymer of tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and vinylidene fluoride (VDF) produced by emulsion polymerization. The resulting dispersion is either processed into powders and pellets or concentrated with emulsifier and supplied in that form to the market.91 Currently, the manufacturer is Dyneon LLC and there are essentially nine commercial grades (five dry and four aqueous dispersions) available that differ in the monomer ratios and consequently in melting points, chemical resistance, and flexibility. 

Gore-Tex nonabsorbable monofilament suture is made from a highly crystalhne hnear PIPE. This fully fluorinated thermoplastic is an addition polymer and is formed by the free radical polymerization route in aqueous dispersion under pressure with persulfates and hydrogen peroxide as initiators. The monomer (tetrafluoroethylene) is made from a two-step process the fluorination of chloroform by HF to produce CHClFj which is subsequently dimerized by pyrolysis to form tetrafluoroethylene. FI FE has the highest enthalpy and entropy of polymerization (-156 kJ/mol and -112 J/ mol-deg, respectively) among the vinyls (Joshi and Zwolinski, 1967). Its molecular weight can be as high as 5 x l(p. 

The aqueous dispersion was coagulated by agitation until a particulate coagulum was obtained which was then separated from water by filtration, rinsed with water, and dried. The dry powder was spread on aluminum trays to a depth of 5 cm and heated for 3 hours at 350°C. The product was a mass of copolymer of tetrafluoroethylene and hexafluoropropylene. It had a melting point of280°C, melt viscosity of 7 x 10" poise. A sample of FEP was chopped into small pieces and... 

Figure 8. Transmission electron micrograph of [dried] commercial aqueous dispersion of as-polymerized poly(tetrafluoroethylene) [Teflon, Du Pont]. PTFE is formed as near-spherical particles of 0.2 pm diameter.

Ethylene and tetrafluoroethylene are copolymerized in aqueous, nonaqueous, or mixed medium with free-radical initiators. The polymer is isolated and converted into extmded cubes, powders, and beads, or a dispersion. This family of products is manufactured by Du Pont, Hoechst, Daikin, Asahi Glass, and Ausimont and sold under the trade names of Tefzel, Hostaflon ET, Neoflon EP, Aflon COP, and Halon ET, respectively. 

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). 

PTFE fluoroplastic n. Polytetrafluoroethylene is prepared by free radical polymerization of tetrafluoroethylene in aqueous systems with persulfate or peroxide initiators to give granular or dispersion polymers. The... 

Hexafluoropropylene and tetrafluoroethylene are copolymerized, with trichlo-racetyl peroxide as the catalyst, at low temperature (43). Newer catalytic methods, including irradiation, achieve copol5mierization at different temperatures (44,45). Aqueous and nonaqueous dispersion polymerizations appear to be the most convenient routes to commercial production (1,46-50). The polymerization conditions are similar to those of TFE homopolymer dispersion polymerization. The copol5mier of HFP-TFE is a random copolymer, that is, HFP imits add to the growing chains at random intervals. The optimal composition of the copolymer requires that the mechanical properties are retained in the usable range and that the MV is low enough for easy melt processing. 

Tetrafluoroethylene (TFE) [116-14-3] and perfluorovinyl ether are copolymerized in aqueous (1,2) or nonaqueous (3) media. The polymer is separated and converted into various forms, such as extruded cubes, powders, beads, or dispersions. This family of products is manufactured by DuPont, Daikin, Dyneon, and Asahi Glass and sold under the trade names of Teflon PFA, Neoflon AP, Hostaflon TFA, and Aflon PFA, respectively. Additional information on speciflc manufacturers products can often be obtained by consulting their internet web sites (for example, www.dupont.com/teflon). 

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