Fluoropolymer Dispersion Processing

This section discusses the coating of surfaces using dispersions and powders of fluoropolymers. A majority of the dispersions consumed are PTFE based some FEP, PFA, PVDF material are also coated on different substrates. Powder coating resins are all melt processible fluoropolymers. Most of the parts used in the chemical processing industry are fabricated by powder coating which is covered in Ch. 8 of this volume. Liquid coatings are used in the rare cases in which powder cannot reach areas of a part with complex geometry. 

This section does not cover the topic of coatings and finishes. These finishes are usually highly formulated and are applied as multiple-pass coatings which include special primers and intermediate layers. They may include pigments, additives, other resins, and more than one fluoropolymer. The main applications of fluoropolymer finishes are in cookware and industrial anticorrosion and high-temperature uses. A separate volume, Fluorinated Coatings and Finishes, a Plastics Design Library (PDL) volume in the Fluorine Handbook Series published by William Andrew, Inc., covers the topic. 

One can think of the PTFE dispersion coating process as impregnation of fibrous or porous materials such as glass fiber, woven glass cloth, and polyaramide fibers and fabrics. The composite product combines the properties of PTFE and substrate. The polytetrafluoroethylene coated or impregnated products are characterized by a number of common attributes, Table 5.9. 

Polytetrafluoroethylene dispersions are aqueous milky dispersions consisting of very ( 0.25 pm) small particles of resin suspended in water. 

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

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. 

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. 

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]. 

The Processing of PTFE Coagulated Dispersion Powders, Technical Service Note F3/4/5, 4th ed., ICI Fluoropolymers, Imperial Chemical Industries PLC, Blackpool, Lancs, U.K., p. 18 (1992). 

Filled or compounded resins contain pigments, surfactants, and other additives to modify the plastic properties. These additives are likely to present risks and hazards in the processing of fluoropolymer compounds. For example, aqueous dispersions of fluoropolymers contain surfactants that may produce... 

Fluoropolymers are notoriously immiscible with any other polymer. Usually, they are dispersed in blends of engineering and specialty polymers either to improve processability or to induce lubricity and abrasion resistance. Examples of the PC/Specialty resin blends are listed in Table 1.68. 

Fluoropolymers are typically synthesized in aqueous polymerization systems (both emulsion and suspension), non-aqueous systems (Freon-113), or Freon-113/aqueous hybrid systems [8]. Such processes require the use of large quantities of water and CFCs (for non-aqueous polymerizations) or fluorinated surfactants (for emulsion polymerization). Aqueous suspension and dispersion poly-... 

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