Polytetrafluoroethylene polymer manufacture

Polytetrafluoroethylene is a completely fluorinated polymer manufactured by free-radical polymerization of tetrafluoroethylene. With a linear molecular structure of repeating -CF2—CF2- units, PTFE is a crystalline polymer with a melting point of 326.7°C. Its specific gravity is 2.13—2.19. Polytetrafluoroethylene has exceptional resistance to chemicals. Its dielectric constant (2.1) and loss factor are low and stable across a wide range of temperature. It has useful mechanical properties from myogenic temperatures to 260°C. In the United States, PTFE is sold as Halon, Algoflon, Teflon, Fluon, Hostaflon, and Polyflon. ... 

Teflon te- flan n. (1) A polymer of fluori-nated ethylene. Very inert, and in the form of a film or an impregnator, used for its heat-resistant and non-sticking properties. (2) Trade name for fluorocarbon resins, including polytetrafluoroethylene, per-fluoropropylene resin, and co-polymers, manufactured by DuPont. 

Many cellular plastics that have not reached significant commercial use have been introduced or their manufacture described in Hterature. Examples of such polymers are chlorinated or chlorosulfonated polyethylene, a copolymer of vinyUdene fluoride and hexafluoropropylene, polyamides (4), polytetrafluoroethylene (5), styrene—acrylonitrile copolymers (6,7), polyimides (8), and ethylene—propylene copolymers (9). 

The high thermal stability of the carbon-fluorine bond has led to considerable interest in fluorine-containing polymers as heat-resistant plastics and rubbers. The first patents, taken out by IG Farben in 1934, related to polychlorotri-fluoroethylene (PCTFE) (Figure 13.1 (a)), these materials being subsequently manufactured in Germany and the United States. PCTFE has been of limited application and it was the discovery of polytetrafluoroethylene (PTFE) (Figure... 

One major use of HF is in the manufacture of fluorinated hydrocarbons. Fluorinated ethylene is used for several specialty polymers. For example, the Teflon coating on nonstick cookware is made from polytetrafluoroethylene (PTFE). This polymer is made from tetrafluoroethylene. 

Darvic, Elvic, Geon, Koroseal, Marvinol, Mipolam, Opalon, Pliofex, Rucon, Solvic, Trulon, Velon, Vinoflex, Vygen, and Vyram are all trade names for poly(vinyl chloride) manufactured by different companies. Some polymers are better known by their trade name than their generic name. For instance, polytetrafluoroethylene is better known as Teflon, the trade name held by DuPont. 

Tetrafluoroethylene is used in the manufacture of polytetrafluoroethylene and other polymers. No information on potential human exposure is available. 

Fluoropolymers are used for the manufacture of coatings for frying pans, pots, fryers and other cooking equipment and utensils. Polytetrafluoroethylene with a melting point of approximately 327 °C is mostly used but polymer mixtures with perfluoro-alkylvinyl ether and hexafluoropropylene can also be used. 

The production of polymeric materials is one of the world s major industries. Polymers are utilized in many applications because of their processability, ease of manufacture, and diverse range of properties. Many of the commonest polymers such as polyethylene, polystyrene, and polytetrafluoroethylene (PTFE) are highly hydrophobic materials rendering them unsuitable for many biomedical applications. For applications that require contact with body fluids such as blood or urine, it is necessary for the materials to be hydrophilic and to be capable of maintaining intimate contact with the fluid in question for prolonged periods of time without significant loss of functional performance. 

Polymeric membranes are prepared from a variety of materials using several different production techniques. Table 5 summarizes a partial list of the various polymer materials used in the manufacture of cross-flow filters for both MF and UF applications. For microfiltration applications, typically symmetric membranes are used. Examples include polyethylene, polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) membrane. These can be produced by stretching, molding and sintering finegrained and partially crystalline polymers. Polyester and polycarbonate membranes are made using irradiation and etching processes and polymers such as polypropylene, polyamide, cellulose acetate and polysulfone membranes are produced by the phase inversion process.f Jf f ... 

For gas filtration, the membrane should be treated to make it hydrophobic if not already inherently so. Membranes made from polytetrafluoroethylene or polypropylene are already nonwetting, and wettable polymers are treated by the manufacturer to render them hydrophobic. If the gas filter is hydrophilic, water condensing on the filter or entrained by the gas will wet the pores and be retained by capillary action unless the differential pressure across the filter exceeds the "bubble-point" pressure. In this case, the filter is "blinded" by water and the flow is restricted considerably. 

There are two common types of membrane material-, microporous and homogeneous. Microporous mate-riiils are manufactured from hydrophobic polymers such as polytetrafluoroethylene or polypropylene, which have a prtrosity (void volume) of about 70% and a pore size of less than I pm. Because of the nonpolar, water-repellent properties of the film, water molecules and electrolyte ions are excluded frrrm the pores gaseous molecules, on the other hand, are free to move in and out of the pores by affusion and thus across this barrier. Typically, the thickness of microporous membranes is about 0.1 mm. 

Active carbons are obtained by partial combustion and foermal decomposition of various raw materials followed by carbonization and activation. A detailed look at the process of pyrolysis and carbonization of a parent feedstock and the processes of generation of an isotropic porous carbon and its activation illustrates the complexity of reactions involved in its manufacturing. Active carbons are manufactured from a wide variety of materials wood [1, 2], coal [1, 2], bituminous coal [29], rubber [30, 31], ahnond shells [32], oil-palm stones [33], polymers (e.g., vinylopyridine resin [34] and polytetrafluoroethylene [35]), phenolic resins [36], rice husk [37], etc. Very interesting active carbon honeycomb structures were fabricated from combination of synthetic precursors, i.e., phenolic resins, along with several organic and inorganic additives [38]. 

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