Polytetrafluoroethylene dispersions

Dispersion Resins. Polytetrafluoroethylene dispersions in aqueous medium contain 30—60 wt % polymer particles and some surfactant. The type of surfactant and the particle characteristics depend on the appHcation. These dispersions are appHed to various substrates by spraying, flow coating, dipping, coagulating, or electro depositing. 

Aqueous corrosion resistance, 13 513 Aqueous dispersion polymerization, 18 291 of acrylonitrile, 11 197-200 Aqueous dispersions, 13 292. See also Aqueous polytetrafluoroethylene dispersions... 

Aqueous perchlorate solutions, 18 274 Aqueous plugs, in microfluidics, 26 968 Aqueous polytetrafluoroethylene dispersions, 18 291 Aqueous potassium permanganate solutions, 15 597-600 Aqueous ring-opening metathesis polymerization (ROMP), 15 495... 

Elliott, E. M. Polytetrafluoroethylene dispersions for metal finishing. Trans. Inst. Metal Finishing 33, 355—365 (1956). 

Co-coagulation is the method by which large quantities of fillers can be incorporated in dispersion polymerized polytetrafluoroethylene. The addition of fillers takes place prior to coagulation of the resin from its dispersion state. In the process of co-coagu-lation, the additives are added to the polytetrafluoroethylene dispersion and mixed. This dispersion is coagulated and the compound is recovered. The smaller the filler particles, the smaller the points of stress rise in the compound will be. Significantly larger quantities of filler can be compounded in PTFE by this technique. 

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

The end uses of polytetrafluoroethylene dispersions are numerous due to the convenience of coating techniques. They can be classified in different ways based on the point of view of product attributes... 

Another approach to the classification of the applications of polytetrafluoroethylene dispersions is the nature of thermal treatment of the fabricated part. Some articles are sintered, some are not sintered but heated to remove the water and surfactant. In some application, the parts are neither sintered nor heated high enough to remove the surfactant. Table 5.11 summarizes the process-based categorization of dispersion applications. 

Polytetrafluoroethylene dispersions may contain one or more surfactants (and other additives) such as perfluoroammoniumoctanoate, also known as C8 in parlance of the industry. There are health hazards associated with some of the surfactants such as C8. 

Glass cloth has a smooth surface and is porous. It does not ionize in water or absorb the polytetrafluoroethylene dispersion. It picks up a small amount of dispersion per pass, therefore requiring multiple passes (up to a dozen) to obtain a smooth surface, if that is required. 

Metal and ceramic surfaces are coated with polytetrafluoroethylene dispersions to protect them from... 

Critical Cracking Thickness - The maximum thickness which can be coated in a single layer (pass) of polytetrafluoroethylene dispersion without crack formation. This thickness is measured after sintering has been completed. 

Impregnation - A term applied to filling or saturation of porous material such as glass cloth and flax with polytetrafluoroethylene dispersion. 

Miura T, Hayashi T, inventors Daikin Industries Ltd, assignee. Aqueous polytetrafluoroethylene dispersion composition and use thereof. United States patent US 6153688. 2000 Nov 28. 

Sintering has been used to produce a porous polytetrafluoroethylene (16). Cellulose sponges are the most familiar cellular polymers produced by the leaching process (123). Sodium sulfate crystals are dispersed in the viscose symp and subsequently leached out. Polyethylene (124) or poly(vinyl chloride) can also be produced in cellular form by the leaching process. The artificial leather-tike materials used for shoe uppers are rendered porous by extraction of salts (125) or by designing the polymers in such a way that they precipitate as a gel with many holes (126). 

Fluorocarbon soHds are rare in defoamer compositions, presumably on account of their cost. SoHd fluorine-containing fatty alcohols and amides are known. The most familiar fluorocarbon soHd is polytetrafluoroethylene [9002-84-0]. Because it is more hydrophobic than siHcone-treated siHca, it might be expected to perform impressively as a defoamer component (14). However, in conventional hydrocarbon oil formulations it works poorly because the particles aggregate strongly together. In lower surface tension fluids such as siHcone and fluorocarbon oils, the powdered polytetrafluoroethylene particles are much better dispersed and the formulation performs weU as a defoamer. 

Many rubber compounds have a tendency to stick in the mould cavity after vulcanisation and require some type of mould release agent. The substances used are surface-active materials such as detergents, soaps, wetting agents, silicone emulsions, aqueous dispersions of talc, mica and fatty acids, applied by spray or brush. Alternatively, dry types based on polytetrafluoroethylene or polyethylene, usually carried in a solvent, can be aerosol applied. An alternative is the addition of an incompatible material to the rubber compound which will bleed to the rubber surface during vulcanisation. 

See also Teflon PTFE-based ionomers, 14 481 PTFE dispersion, 18 288. See also Polytetrafluoroethylene (PTFE)... 

The general structure of this class of materials can, therefore, be summarized as a fine dispersion of metal oxide in a polymer matrix very similar to plasma polytetrafluoroethylene and in principle any metal should be able to be incorporated. Clearly, if the films are protected from the atmosphere, for metals which form involatile fluorides having a relatively weak metal-fluorine bond strength, it should be possible to produce films having metal atoms dispersed in the matrix. It is expected that these films will have many interesting chemical, optical, electrical and magnetic properties., ... 

Fluorocarbon Resins. This term includes polytetrafluoroethylene, polymers of chloro-trifluoroethylene (fluorothene), vinylidene fluoride (H2C CF2)j hexafluoropropylene (C3Ffl) and similar compds. These polymers are thermoplastic, inert to chemicals and oxidation. They have high heat stability, retain their useful props at both extremely low and high temps, have high electrical resistance to moisture. The materials are available as re sins, powders, and dispersions, and as films, sheets, tubes, rods and tapes. Some of them are rubber-like. Commercially available varieties are Kel-F , Teflon , Fluorel , Aclar and "Halon ... 

Many semicompatible rubbery polymers are added to increase the impact resistance of other polymers, such as PS. Other comminuted resins, such as silicones or polyfluorocarbons, are added to increase the lubricity of other plastics. For example, a hot melt dispersion of polytetrafluoroethylene (ptfe) in polyphenylene sulfide (PPS) is used as a coating for antistick cookware. 

The modified parfait method developed here replaced silica gel with porous polytetrafluoroethylene (PTFE, Teflon). Properly wetted Chromosorb T, an aggregate of aqueous dispersion-polymerized PTFE, is an efficient adsorbent for many hydrophobic substances in water... 

Fig. 1 a and b. Micrographs of granular and dispersion particles of polytetrafluoroethylene. a) Cross-section of... 

The extrusion of lubricated powders, which has been described by Lontz, Jaffe, Robb, and Happoldt, is a unique method for fabricating polytetrafluoroethylene. An aqueous dispersion is coagulated by mechanical agitation. The powder is then dried and blended with 18—20% of a... 

C is clearly an important quantity for a latex dispersion since it essentially represents the electrolyte concentration at which complete loss of stability occurs. It may be obtained experimentally by a variety of different methods (14,17, 18,19). It should be noted, however, that since coagulation is a kinetic phenomena time enters as a variable and consequently the various methods may yield somewhat different numerical results. This effect is illustrated by results obtained for the coagulation of polytetrafluoroethylene (PTFE) latices with sodium chloride as a function of pH (19). From Figure 4 it can be seen that different results are obtained according to whether the system was examined after 2 h or 24 h. As expected the results indicate that the state of aggregation is more advanced after 24 h and consequently systems at a lower electrolyte concentration have coagulated. Care must therefore be taken when comparing values... 

Ottewill and Ranee (29) using well-dialysed PTFE latices obtained the results shown in Figure 6. The change in c.c.c. with pH is clearly defined but the c.c.c. above pH 5 is at a fairly high concentration of electrolyte and insufficient positive charge is built up to stabilise the dispersion. It is also possible with this system that the very hydrophobic polytetrafluoroethylene parts of the surface do not adsorb the hydrolysed species and in the well-dialysed system adsorption can only occur on the sparse charged sites. 

Semihydrophobic electrodes are made from an active electrode material (- electrocatalyst), a binder (dissolved polymer), and a hydrophobizing agent (e.g., dispersion of polytetrafluoroethylene PTFE). Upon thorough mixing a slurry is obtained, which is spread onto a material serving as mechanical carrier and in most cases also as current collector. After removal of the solvent a porous layer/sheet is obtained. Upon contact with an aqueous electrolyte solution various interactions are possible [ii] ... 

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