Fluorocarbons process

Hegemann [36] reviewed plasma polymerization processes as a means to achieve hydrophobic surface properties of textiles, discussing the possibilities of using hydrocarbon, organosilicon, fluorocarbon process gases. A typical example of this process design based on the use of a fluorocarbon is described by Zhang et al. [37]. It should be mentioned here that in contrast to a photo-chemical process as is dis-... 

Figure 8. Influence of F/C ratio of a fluorocarbon process gas on the occurrence of CF2- and CF3-radicals in the plasma [40]. According to their spectroscopic properties, CF2-radicals can best be detected in the plasma by UV absorption, while CF3-radicals are detected by UV emission.

Certain fluorocarbon processing aids are known to partially alleviate melt defects in extrudable thermoplastic hydrocarbon polymers and allow for faster, more efficient extrusion. Blatz first described the use of fluorocarbon polymer process aids with melt extrudable hydrocarbon polymers wherein the fluorinated polymers are homopolymers and copolymers of fluorinated olefins having an atomic fluorine to carbon ratio of at least 1 2, wherein the fluorocarbon polymers have melt flow characteristics similar to that of the hydrocarbon polymers (4). 

Talc is commonly added to film resins to prevent blocking in the resulting film. Concentrations from 1,000 to 10,000 ppm are commonly used. Luzenac America offers selected talc products that provide the optimal coag>romlse between film property retention and antiblock performance. A surface modified product is also offered where melt fracture or interactions with fluorocarbon processing aids needs to be minimized. 

Liquid or solid films which reduce or prevent adhesion between surfaces solid-solid, solid-paste, solid-liquid. Waxes, metallic soaps, glycerides (particularly stearates), polyvinyl alcohol, polyethene, silicones, and fluorocarbons are all used as abherents in metal, rubber, food, polymer, paper and glass processing. 

In the North American HF market, approximately 70% goes into the production of fluorocarbons, 4% to the nuclear industry, 5% to alkylation processes, 5% to steel pickling, and 16% to other markets (41). This does not include the HF going to aluminum fluoride, the majority of which is produced captively for this purpose. 

The nonbonding electron clouds of the attached fluorine atoms tend to repel the oncoming fluorine molecules as they approach the carbon skeleton. This reduces the number of effective coUisions, making it possible to increase the total number of coUisions and stiU not accelerate the reaction rate as the reaction proceeds toward completion. This protective sheath of fluorine atoms provides the inertness of Teflon and other fluorocarbons. It also explains the fact that greater success in direct fluorination processes has been reported when the hydrocarbon to be fluorinated had already been partiaUy fluorinated by some other process or was prechlorinated, ie, the protective sheath of halogens reduced the number of reactive coUisions and aUowed reactions to occur without excessive cleavage of carbon—carbon bonds or mnaway exothermic processes. 

In early reaction systems (9,10,31,32) the vaporized hydrocarbon was combined with nitrogen in a reactor and mixed with a nitrogen—fluorine mixture from a preheated source. The jet reactor (11) for low molecular weight fluorocarbons was an important improvement. The process takes place at around 200—300°C, and fluorination is carried out in the vapor state. 

Fluorocarbons are made commercially also by the electrolysis of hydrocarbons in anhydrous hydrogen fluoride (Simons process) (14). Nickel anodes and nickel or steel cathodes are used. Special porous anodes improve the yields. This method is limited to starting materials that are appreciably soluble in hydrogen fluoride, and is most useflil for manufacturing perfluoroalkyl carboxyflc and sulfonic acids, and tertiary amines. For volatile materials with tittle solubility in hydrofluoric acid, a complementary method that uses porous carbon anodes and HF 2KF electrolyte (Phillips process) is useflil (14). 

Teflon FEP—Fluorocarbon Resin—Techniques for Processing bj Melt Extrusion, 2nd ed., information bulletin X-82, E. I. du Pont de Nemours Co., Inc., Wilmington, Del., 1960. 

Peifluoioalkoxy (PFA) fluoiocaibon lesins aie designed to meet industry s needs in chemical, electrical, and mechanical appHcations. These melt processible copolymers contain a fluorocarbon backbone in the main chain and randomly distributed perfluorinated ether side chains ... 

The elastomer process is very similar to the Dennis process. It involves a number of steps in which a gas, formerly carbon dioxide and now fluorocarbon, is mixed with a plastisol under pressure. When released to atmospheric pressure, the gas expands the vinyl compounds into a low density, open-ceUed foam which is then fused with heat. 

The polymei latex is then coagulated by addition of salt oi acid, a combination of both, oi by a fiee2e—thaw process. The cmmb is washed, dewatered, and dried. Since most fluorocarbon elastomer gums are sold with incorporated cure systems, the final step in the process involves incorporation of the curatives. This can be done on a two-roU mill, in an internal mixer, or in a mixing extmder. 

Extruded Articles. In extmded article compounding, the most important parameters are scorch safety and flow characteristics (53). The bisphenol cure system again offers the best scorch resistance of the available fluorocarbon elastomer cure systems. Good flow characteristics can be achieved through proper selection of gum viscosities. Also, the addition of process aids to the formulation can enhance the flow characteristics. Typical formulations for extmsion grade fluorocarbon elastomers are given iu Table 7. 

Commonly accepted practice restricts the term to plastics that serve engineering purposes and can be processed and reprocessed by injection and extmsion methods. This excludes the so-called specialty plastics, eg, fluorocarbon polymers and infusible film products such as Kapton and Updex polyimide film, and thermosets including phenoHcs, epoxies, urea—formaldehydes, and sdicones, some of which have been termed engineering plastics by other authors (4) (see Elastol rs, synthetic-fluorocarbon elastol rs Eluorine compounds, organic-tdtrafluoroethylenecopolyt rs with ethylene Phenolic resins Epoxy resins Amino resins and plastics). 

Polymers used for seat and plug seals and internal static seals include PTFE (polytetrafluoroeth ene) and other fluorocarbons, polyethylene, nylon, polyether-ether-ketone, and acetal. Fluorocarbons are often carbon or glass-filled to improve mechanical properties and heat resistance. Temperature and chemical compatibility with the process fluid are the key selec tion criteria. Polymer-lined bearings and guides are used to decrease fric tion, which lessens dead band and reduces actuator force requirements. See Sec. 28, Materials of Construction, for properties. 

Hydrogen fluoride accounts for about 907o of the gaseous fluoride emitted from the electrolytic cell. Other gaseous emissions are SO2, COj, CO, NO2, HjS, COS, CS2, SFg, and various gaseous fluorocarbons. Particulate fluoride is emitted directly from the process and is also formed from condensation and solidification of the gaseous fluorides. 

Almost all of the biomedical research done in the 25 years following the liquid-breathing work was conducted with commercially available fluorocarbons manufactured for various industnal uses by the electrochemical Simons process (fluonnation in a hydrofluoric acid solution) or the cobalt fluoride process (fluori-nation with this solid in a furnace at about 200 C) These processes tended to yield many by-products, partly because they were, to some extent, free radical reactions and partly because it was difficult to easily achieve complete fluonnation Aromatic hydrocarbons gave better products with the cobalt tnfluonde [73] method, whereas saturated hydrocarbons yielded better products with fluonnation using diluted or cooled gaseous fluorine (Lagow) Incompletely fluormated matenal was either... 

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