Chemical resistance fluoropolymers

Synthetic rubbers, EPM/EPDM, nitrile, polychloroprene (neoprene), epichlorohydrin, and polyacrylate have good oil resistance, heat stability, and chemical resistance. Fluoropolymers are used in oil and gas wells 20,000 ft (6096 m) deep. These depths can have pressures of 20,000 Ib/in (137.5 MPa) which cause extrusion failures of down-hole seals by forcing the rubber part out of its retaining gland. TFE/propy-lene jackets protect down-hole assemblies which consist of stainless steel tubes that deliver corrosion-resistant fluid into the well. 

Partially fluorinated materials are ECTFE, ETFE, and PVDF. These materials have higher mechanical properties but lower temperature (<300°F/150°C) and chemical resistance. Fluoropolymer linings can cost 5-20 times more than thermoset linings so they are typically restricted to elevated temperature environment. 

A 50 50 mol/mol copolymer of hexafluoroisobutylene (CH2 = C(CF3)2) and vinylidene fluoride was made available by Allied Chemical in the mid-1970s as CM-1 Fluoropolymer. The polymer has the same crystalline melting point as PTFE (327°C) but a mueh lower density (1.88g/cm ). It has excellent chemical resistance, electrical insulation properties and non-stiek characteristics and, unlike PTFE, may be injeetion moulded (at 380°C). It is less tough than PTFE. 

Non-Metallic Materials Numerous engineering thermoplastics have been commercialised including materials such as polyetherether ketone (PEEK) and polyether sulphate (PES) with much improved thermal/chemical resistance. The usage of FRP equipment has increased, and fluoropolymer lining technology/applications have come of age. Of particular interest is the development of stoved, fluoropolymer coating systems for process industry equipment. 

Selection of Corrosion-Resistant Materials The concentrated sofutions of acids, alkalies, or salts, salt melts, and the like used as electrolytes in reactors as a rule are highly corrosive, particularly so at elevated temperatures. Hence, the design materials, both metallic and nonmetallic, should have a sufficiently high corrosion and chemical resistance. Low-alloy steels are a universal structural material for reactors with alkaline solutions, whereas for reactors with acidic solutions, high-alloy steels and other expensive materials must be used. Polymers, including highly stable fluoropolymers such as PTFE, become more and more common as structural materials for reactors. Corrosion problems are of particular importance, of course, when materials for nonconsumable electrodes (and especially anodes) are selected, which must be sufficiently stable and at the same time catalytically active. 

The heat resistance and chemical resistance of the fluoropolymers is mainly dependent on the extent of fluorination and stability of the crosslinks. For example, most fluorocarbons have fluorine contents of 50-70%, more chemically resistant types 65-69%. For comparison, fluorosilicones contain about 36% fluorine. 

One of the first fictional fluoropolymers was poly-1,2,2-trifluorostyrene. On one hand, it has much better oxidation and chemical resistance in comparison with common hydrocarbon polymers and, on the other hand, a wide range of functional groups can be attached to the aromatic ring. A sulfonated polymer was successfully used as a membrane for fuel cells by General Electric Co.3... 

Nonstickiness, low friction, low wettability, and high thermal- and chemical-resistance are the major properties of PTFE, which was accidentally discovered in the DuPont laboratories in 1938, and these properties are more or less typical of other fluoropolymers that have been developed since. 

Amorphous fluoropolymers have many applications in the areas of advanced materials where they are used in applications requiring thermal and chemical resistance. Their manufacture is hindered by their low solubility in many solvents. Many fluoropolymerizations cannot be carried out in hydrocarbon solvents because the radical abstraction of hydrogen atoms leads to detrimental side reactions. Chlorofluorocarbons (CFCs) were thus commonly used, but their use is now strictly controlled due to their ozone depleting and greenhouse gas properties. Supercritical carbon dioxide is a very attractive alternative to CFCs and it has been shown that amorphous fluoropolymers can be synthesized by... 

Fluoropolymers are another class of material that finds utility in wire and cable constructions due to high service temperatures, chemical resistance, dielectric performance, and inherent flame retardancy. 

Teflon PFA (perfluoroalkoxy). This plastic is translucent and slightly flexible. It has the widest temperature range of the fluoropolymers — from -270°C to +250°C — with superior chemical resistance across the entire range. Compared to TFE at +277°C, it has better strength, stiffness, and creep resistance. PFA also has a low coefficient of friction, possesses outstanding antistick properties, and is flame-resistant. 

Halar ECTFE (ethylenechlorotrifluoroethylene) This material is an alternating copolymer of ethylene and chlorotrifluroethylene. This fluoropolymer withstands continuous exposure to extreme temperatures and maintains excellent mechanical properties across this entire range (from cryogenic temperatures to 180°C). It has excellent electrical properties and chemical resistance, having no known solvent at 121°C. It is also nonbuming and radiation-resistant. Its ease of processing affords a wide range of products. 

In operation containers constructed of microwave-transparent materials, (e.g. quartz or fluoropolymers), are used to hold multiple samples inside the ultraCLAVE . The interior of the stainless steel vessel is protected by a titanium nitride or multi-layer PTFE plasma coating for complete acid and chemical resistance. Sample containers may be open or covered by a lid. After the samples are loaded (manually or robotically) the ultraCLAVE cover is lowered into place by an electric motor controlled from the system s PC. The vessel closure is engaged and secured in place to seal the ultraCLAVE for high pressure operation. 

Certain substrates (woven and nonwoven fabrics, foils, and films) are coated by dipping, spreading, or spraying with fluoroelastomers in liquid form. The older method using a solution of fluoroelastomers in volatile solvents (e.g., methyl ethyl ketone, toluene) is gradually being replaced by the use of water-based latexes. Fluoroelastomer latexes can also be used for chemically resistant and heat-resistant coatings. Some fluoropolymer producers offer latex in limited quantities to processors skilled... 

In general, fluoropolymers provide solutions to the industry demands for higher service temperatures, better electrical properties, chemical resistance, improved flame resistance, and reduced smoke generation. 

Of the melt-processible fluoropolymers, which are the most suitable for tubing, PFA provides the extreme thermal and chemical resistance required in the pharmaceutical processing. PFA, however, does not have the physical strength of PTFE at elevated temperatures... 

Third 1965 PPS, polyimides, aromatic polyesters, aromatic polyamides, fluoropolymers, thermoplastic elastomers High mechanical strength, very high melting point, superior chemical resistance... 

Properties of fluoropolymers that have led to applications include chemical resistance, thermal stability, cryogenic properties, low coefficient of friction, low surface energy, low dielectric constant, high volume and surface resistivity, and flame resistance. Fluoropolymers are used as liners (process surface) because of their resistance to chemical attack. They provide durable, low maintenance and economical alternatives to exotic metals for use at high temperatures without introducing impurities. Electrical properties make fluoropolymers highly valuable in electronic and electrical applications as insulation, e.g., FEP in data communications. 

PVDF components are used extensively in the high purity semiconductor market (low extractible values), pulp and paper industry (chemically resistant to halogens and acids), nuclear waste processing (radiation and hot acid applications), and the general chemical processing industry (chemical and temperature applications). Fluoropolymers have also met specifications for food and pharmaceutical processing industries. 

Polytetrafluoroethylene (PTFE Teflon) was discovered accidently by PlunkettCZ nd commercialized by DuPont in the 1940 s. This polymer has a solubility parameter of about 6H and a high melting point of 327°C and is not readily moldable. Poly-chlorotrifluoroethylene (CTFE, Kel-F), the copolymer of tetrafluoroethylene and hexafluoropropylene (FEP), polyvinylidene fluoride (PVDF, Kynar), the copolymer of tetrafluoroethylene and ethylene (ETFE), the copolymer of vinylidene fluoride and hexafluoroisobutylene (CM-1), perfluoroalkoxyethylene (PFA) and polyvinyl fluoride (PVF, Tedlar) are all more readily processed than PTFE. However, the lubricity and chemical resistance of these fluoropolymers is less than that of PTFE. 

Polymers with elastomeric properties have been obtained since the 1960s by copolymerization of tetrafluoroethylene vith trifluorovinyl ethers such as heptafluoropropyl trifluorovinyl ether (PPVE). These so-called second-generation fluoropolymers combine high thermal and chemical resistance with elasticity and are used for coatings, seals, and other parts which can be produced by conventional extrusion and molding processes. 

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