Fluoroelastomers chemical resistance

Fluoroelastomers. The fluoroelastomers were introduced to the mbber industry in the late 1950s by the DuPont Company. They were made by modification of Teflon polymers and designed to have exceUent heat and chemical resistance, but remain elastomeric in nature. They were very expensive and have found use in limited appHcations. However, with the increasing demand in the automotive and industrial market for improved reHabUity and longer Hfe, the elastomeric fluoroelastomers have made significant inroads into these appHcations (see Elastomers, synthetic-fluorocarbon ELASTOTffiRS). 

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... 

DuPont Performance Elastomers, Chemical Resistance Guide, Version 6.0 (August 2006) Overview of Elastomers and Elastomer Materials, ElastomeFs Characteristics, Fluoroelastomer (Viton. FKM) and Nitrile, hydrogenated Nitrile (NBR, HNBR), Available at http /www.dupontelastomers. com/Tech Info/chemical.asp (accessed October 7, 2006). 

Fluoroelastomers are fluorine-containing hydrocarbon polymers with a saturated structure obtained by polymerizing fluorinated monomers such as vinylidene fluoride, hexafluoropropene, and tetrafluoroethylene. The result is a high-performance s)mthetic rubber with exceptional resistance to oils and chemicals at elevated temperatures. Initially, this material was used to produce O-rings for use in severe conditions. Although this remains a major area of application, these compoimds have found wide use in other applications because of their chemical resistance at high temperatures and other desirable properties. 

Perfluoroelastomers provide the elastomeric properties of fluoroelastomers and the chemical resistance of PTFE. These compounds are true rubbers. Compared with other elastomeric compounds, they are more resistant to swelling and embrittlement and retain their elastomeric properties over the long term. In difficult environments, there are no other elastomers that can outperform the FPMs. These s)mthetic rubbers provide the sealing force of a true elastomer and the chemical inertness and thermal stability of polytetra-fluoroethylene. 

Fluoroelastomers can be polymerized with copolymers and terpolymers of tetrafluoroethylene, hexafluoroethylene, and vinylidene fluoride. The fluorine content largely determines chemical resistance and Tg, which increases with increasing fluorine content. Low-temperature flexibility decreases with increasing fluorine content. The fluorine content is typically 57% wt. ... 

Fluoroelastomers combine excellent chemical resistance (e.g. oxidizing acids, and alkalis) and high-temperature resistance (i.e., up to 275-300°C for short periods of time) excellent oxidation resistance good resistance to fuels containing up to 30% aromatics mostly poor resistance in solvents or organic media by contrast with fluorinated plastics. 

Viton A fluoroelastomer material that provides exceptional chemical resistance to chlorinated and aromatic solvents. Viton is very flexible, but has minimal resistance to cuts and abrasions. 

At least one terpolymer of the type described above has been introduced commercially (Kalrez) and this has been considered by its manufacturers (Du Pont) as the forerunner of a new generation of fluoroelastomers. The chemical resistance of the polymer is outstanding. In particular vulcanizates can withstand air oxidation to temperatures in the range 290-315°C and exhibit an extremely low volume swell in a wide range of solvents. Both of these characteristics are unmatched in any other commercial fluoroelastomer. (Certain fluorine-containing triazines do show superior heat resistance but are not of commercial significance—see Section 13.7.)... 

Kalrez Dupont s trade name for fluoroelastomers made from tetrafluoroethylene, perfluorovinylmethyl ether, and a small percentage of crosslinkable monomer. These elastomers combine the rubbery properties of Viton with the thermal stability, chemical resistance, and electrical characteristics of tetrafluoroethylene resin. (Handbook of plastics, elastomers and composites. 4th edn. Harper CA (ed). McGraw-Hill, New York, 2002 Ash M, Ash I (1982-1983) Encyclopedia of plastics polymers, and resins, vols I-III. Chemical Publishing, New York). 

Fluoroelastomers are increasingly in demand to meet California Air Resources Board (CARB) requirements by 2004, which limit evaporative hydrocarbon emissions. Dy-neon fluoroelastomers, with low permeation number in alcohols and reformulated gaso-hnes, are used in the fuel delivery system, fuel lines, vapor hnes, O-rings, and custom seals. Dyneon BRE base-resistant elastomers are formulated for resistance to amine additives in automatic transmission fluids (ATF), engine oils, and gear lube oils— in addition to properties in other Dyneon fluoroelastomers including high temperature and chemical resistance. ... 

Vitron A fluoroelastomer material that provides exceptional chemical resistance to... 

FKM 2 Fluoroelastomer Standard or specialty type fluorocarbon. Typically, >66% fluorine Same as FKM 2. Greater chemical resistance Ketones, low molecular weight esters and nitro-containing compounds... 

Another category of fluoroelastomers, called FEPM has been created recently for base resistant fluoroelastomers. For higher temperature and chemical resistance fiiUy fluorinated materials, called perfluoroelastomers, are available in the form of molded seals and parts, such as Kalrez perfluoroelastomers parts and Chemraz Perfluoroelastomer Compounds. They bear the classification of JK or HK depending on supplier and compound offered, JK offering a continuous service temperature of 315°C. FFKM compounds are available from most FKM suppliers but gums are rarely available and in this chapter we focus on fluoroelastomers FKM and FEPM. 

Chemical resistance is the other main attribute of fluoroelastomers with excellent resistance to fuels, solvents, and oils. Steam and acid resistance is satisfactory with bisphenol cured FKM, and very good with peroxide cured FJCM (Table 4.1). Strong... 

Fluoroelastomer compounds, although more costly than most mid-performance elastomers, provide additional value with heat, chemical resistance, and longer seal life. Figure 4.3 expresses the value in use versus the cost per liter (more adapted as part prices are volume based, whereas material prices are mass based). 

TFE (tetrafluoroethylene), a third monomer was soon introduced to increase the fluorine level of fluoroelastomers and increase their chemical resistance, particularly to alcohols. TFE is usually added at the expense of VF2, reducing hydrogen content, whereas HFP is maintained at sufficient levels to break crystallinity. 

The two major differentiators for fluoroelastomers are chemical resistance (specifically, base resistance and oxygenated fuel resistance) and low-temperature flexibUity. 

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