Coagulation-dispersion

The discovery of PTFE (1) in 1938 opened the commercial field of perfluoropolymers. Initial production of PTFE was directed toward the World War II effort, and commercial production was delayed by Du Pont until 1947. Commercial PTFE is manufactured by two different polymerization techniques that result in two different types of chemically identical polymer. Suspension polymerization produces a granular resin, and emulsion polymerization produces the coagulated dispersion that is often referred to as a fine powder or PTFE dispersion. 

Emulsion polymerization a sufficient amount of dispersing agent and mild agitation is employed. This produces small colloidal particles dispersed in the aqueous reaction medium. In this procedure, called aqueous dispersion polymerization, precipitation of the resin particles is avoided. The coagulated dispersion produced by emulsion polymerization is often called a fine-powder or PTFE dispersion. 

The equation derived by Troelstra and Kruyt is only valid for coagulating dispersions of colloids smaller than a certain maximum diameter given by the Rayleigh condition, d 0.10 A0. Equation 4 applies in cases where particles are transported solely by Brownian motion. Furthermore, the kinetic model (Equations 2 and 3) has been derived under the assumption that the collision efficiency factor does not change with time. In the case of some partially destabilized dispersions one observes a decrease in the collision efficiency factor with time which presumably results from the increase of a certain energy barrier as the size of the agglomerates becomes larger. 

J. A. Jaffe, L. E. Robb and W. B. Happoldt jr. Teflon" tetrafluoroethylene resin dispersion-extrusion properties of lubricated resin from coagulated dispersion. Ind. and Eng. Chem. 44, 1805 — 1810 (1952). 

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). 

Magnifloc [Cytec]. TM for water soluble polymers for flocculation, coagulation, dispersion, and viscosification. 

Incorporation of aqueous dispersions of antimony pentoxide into latex requires a pH adjustment prior to adding it to latex to prevent latex coagulation. Dispersions of antimony pentoxide usually have a pH = 5 which is too low for use in most latex formulations. Adjustment of pH can be made with ammonia but prior to such a pH adjustment it is necessary to dilute the dispersion to a concentration below 40% SbzOs. 

The coagulation-dispersion behavior of aqueous silica sols is central to almost all processes requiring their unique adsorption, dispersion, gelation, and sol-gel properties. Aqueous silica sols are of particular interest in colloid science because their coagulation-dispersion behavior is said to be anomalous , that is, their stability in terms of electrolyte-pH control does not follow the pattern followed by almost all other oxide and latex colloidal materials. This chapter examines aqueous silica sol coagulation effects in light of studies of macroscopic silica-water interfaces and in particular the electrical double layer at such interfaces. 

This section discusses the fabrication of PTFE, known asfine powder or coagulated dispersion powder, into shapes and articles. The most common fabricated commercial forms include rods, tapes, wire insulation, tubing, sheeting, and other profiles. Tube diameters range from a fraction of a millimeter to almost a meter with wall thicknesses of 100 pm to a few millimeters. Rods up to 5 cm diameter can be produced and calendared, prior to sintering, to produce tapes. Unsintered tapes are broadly applied as... 

The Processing of PTFE Coagulated Dispersion Powder, Fluon PTFE Resins, Imperial Chemical Industries, Ltd.(1986)... 

Coagulated Dispersion Powder - An alternative name for fine powder polytetrafiuoroethylene. See also Fine Powder PTFE. 

These processes depend on fluid shear for coagulant dispersal and for promoting particle contacts. Shear is most commonly introduced by mechanical mixing equipment. In certain solids contact processes shear results from fluid passage upward... 

WWW. age. CO. j p/english G200 series presintered extrusion powders G300 series agglomerated (free flowing) Fluon PTFE coagulated dispersion powders GDI series low reduction ratio polymers CDO series high reduction ratio copolymers... 

Modifying surfactant properties flocculating, coagulating, dispersing, stabliz-ing, emulsifying, suspensions antifoam properties. 

Figure 15. Stability domain of a hematite hydrosol (2.9 pg cm ) in the presence of citric acid as a function of the pH, 1 h after mixing the reacting components at 25°C. The critical coagulation concentrations (c.c.c.) are indicated by o, and critical restabilization concentrations (c.s.c.) by A. Shaded areas designate coagulated dispersions [27].

Wang, C. S. A Mathematical Study of Particle Size Distribution of Coagulating Disperse Systems, Ph.D. Thesis, California Institute of Technology, Pasadena, CA, 1966. 

Invention of Lubricated Extrusion for Coagulated Dispersion Polymer JJ. Lontz, et al. Ill]... 

Commercially, PTFE is available in three different forms that come from two different types of polymerization. These materials are known as granular polymer, aqueous dispersions, and coagulated dispersion products, often referred to as "fine powder. Specifications for each of these materials have been prepared by the American Society for Testing and Materials and pertinent ASTM standards are listed in Table iv. These standards are a source of much useful information about PTFE that is not readily available elsewhere. 

Dried coagulated dispersion PTFE ("Fine Powder") is blended with organic "lubricant". 

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