Fluoropolymer dispersions

Powdered PTFE is easily dispersed directly into PFCs and the dispersion can be apphed to a substrate using dip-coating, spraying, painting, and spin-coating. Agitation is required to maintain a homogeneous dispersion. 

Some PTFE products are supplied as dispersions. Prior to the phase-out of CFCs, Vydax was used as a dispersion of sohd PTFE in Freon -113 (1,1,2- 

Solubility of fluorocarbons High High High High High 

Flash point (°C) None None None None None 

Solvent Boiling point ( C) Vapor pressure (mm Hg) Heat of vaporization (cal/g at boiling point) 

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ISO 12086-1 1995 Plastics - Fluoropolymer dispersions and moulding and extrusion materials -Part 1 Designation system and basis for specifications ISO 12086-2 1995 Plastics - Fluoropolymer dispersions and moulding and extrusion materials - Part 2 Preparation of test specimens and determination of properties... 

Prior to their current phase-out, chlorofluorocarbons (CFCs) were widely used as processing solvents for various materials. CFCs were well suited for many medical applications owing to their high solvency, nonflammability, good materials compatibility, and low toxicity. The uses for CFCs include a silicone deposition solvent, a fluoropolymer dispersion liquid, and processing solvents. However, the Montreal Protocol phase-out of ozone-depleting substances has required that alternative dispersants and solvents be found. Limitations of most available alternatives include flammability, low volatility, poor solvency, and poor materials compatibility. 

Table 6.2. Evaporative Properties of Various Fluoropolymer Dispersants...

Dadalas, M.C., Epsch, R., Kloos, E.,and Harvey, L.W. Fluoropolymer dispersions containing no or little low molecular weight fiuorinated surfactant, U.S. Patent 7,279,522 (October 9, 2007) to 3M Innovative Properties Co. 

Visca M et al. (2003) Aqueous fluoropolymer dispersions containing bifimctional fluorinated surfactants with reduced environmental impact. World Appl 2,003,279,9. Solvay Solexis S.p.A., Italy... 

Hintzer K et al. (2007) Method of making fluoropolymer dispersion. US Appl 2,007,015,864. 3M Innovative Properties Company, USA... 

Industrial and crmsumcu uses Fluoropolymer manufacture (APFO) Fluoropolymer dispersion processing 1951-2004 2,000-4,000 ... 

Emulsifier Recovery/Removal from Fluoropolymer Dispersions Fluo-ropolymer dispersions contain all of the fiuorinated emulsifier used during the polymerization step unless a part of it is lost during workup (e.g., up-concentration) and stabilization with nonionic nonfluorinated emulsifiers. In any event, some fiuorinated emulsifier always remains in the dispersion, as all of these steps cannot remove the fiuorinated emulsifier completely, even if they are applied several times, for example, by up-concentration via ultrafiltration with repeated dilution of the up-concentrated dispersion [26]. Although further processing of fluoropolymer dispersions usually destroys the bulk of the fiuorinated emulsifier, it is desirable to recover and reuse the expensive polymerization aid completely while keeping or even improving the quality of the dispersions. 

Emulsifier Removal by Other Methods One approach to reduce the emulsifier content of fluoropolymer dispersions is based on the thermal degradation of the emulsifiers at sufficiently high temperatures [43]. To avoid adverse effects for the dispersion, a nonionic stabilizer is added. The stabilized dispersion is heated... 

Up-concentration of fluoropolymer dispersions is often carried out by the addition of nonionic surfactants followed by heating. The mixture separates in two phases. The upper, clear phase is separated by decantation. It contains a part of the fluorinated emulsifier [47,48]. 

Ultrafiltration of fluoropolymer dispersions using oscillating membranes results in a permeate containing a part of the fluorinated emulsifier. After dilution of the up-concentrated dispersion with water and nonionic surfactant, the ultrafiltration is repeated. This process may be carried out several times, resulting in an up-concentrated fluoropolymer dispersion with low fluorosurfactant content [49]. 

ISO 12086 Plastics-Fluoropolymer dispersions, and moulding and extrusion materials Part 1, Designation system and bases for specifications (ISO 12086-1 2006 CEN, Bruxelles). 

Konabe K. Fluoropolymer dispersion and electrode composition containing same. US Patent 20060078800. 2006 Apr 13. 

Plastics - Fluoropolymer dispersions and molding and extrusion materials Part 1 Designation system and basis for specifications... 

Fabrics that cannot be finished with aqueous fluoropolymer dispersions can be finished by spray application of a fluoropolymer dispersed in a volatile solvent, such as stabilized trichloroethylene [150] or tetrachloroethylene [151]. After spraying, fabrics pass directly from the spray booth into a dryer heated at 38-66°C. The finish is cured for 60 s at 150°C or at a lower temperature if the fabric cannot tolerate heating at 150°C [150]. Equipment has been built for continuous pad-dry-heat application of fluoropolymers from a volatile solvent, which is recovered almost completely and recycled [151]. The use of volatile solvents has caused environmental concerns. 

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