Elastomers Viton, fluorinated

Elastomers containing fluorine, also called fluorelastomers. These combine the good physical properties of organic elastomers with the thermal stability of inorganic materials. Trade names are Viton, Fluorel, Kel-F and Technoflon. 

I, Nitrile elastomer (Perbunan) II, fluorinated elastomer (Viton) III, silicone elastomer. 

In the 1960s and 1970s, additional elastomers were developed by Du Pont under the Viton and Kalrez trademarks for improved low temperature and chemical resistance properties using perfluoro(methyl vinyl ether), CF2=CFOCF3, as a comonomer with vinyUdene fluoride and/or tetrafluoroethylene (12,13) (see Fluorine compounds, organic-tethafluoroethylene polypous and copolyp rs). 

Even if several articles and patents deal with the cotelomerisation or copolymerisation of HFP with other fluorinated olefins (e.g., with vinylidene fluoride leading to well-known Viton elastomers), its homotelomerisation is not so easy. This may come from the fact that hexafluoropropene is a monomer which... 

Kalrez (perfluoro-elastomer) All chemicals Alkali metals and fluorine Typical color black. Temperature range -37 to 260°C. Firm compression. Density 2.02. Chemically inert properties similar to Teflon, but mechanically similar to Viton. Very expensive. 21.50... 

The thermal stability of fluorocarbon elastomers also depends on their molecular structure. Fully fluorinated copolymers, such as copolymer of TFE and PMVE (Kal-rez), are thermally stable up to temperatures exceeding 300°C (572°E). Moreover, with heat aging this perfluoroelastomer becomes more elastic rather than embrittled. Eluorocarbon elastomers containing hydrogen in their structures (e.g., Viton, Dyneon, and DAI-EL EKM) exhibit a considerably lower thermal stability than the perfluori-nated elastomer. Eor example, the long-term maximum service temperature for FKM... 

Most commercial fluorocarbon elastomers have brittle points between -25°C (-13°F) and -40°C (-40°F). The low-temperature flexibility depends on the chemical structure of the polymer and cannot be improved markedly by compounding. The use of plasticizers may help somewhat, but at a cost of reduced heat stability and worsened aging. Peroxide-curable polymers may be blended with fluorosilicones, but such blends exhibit considerably lower high-temperature stability and solvent resistance and are considerably more expensive than the pure fluorocarbon polymer. Viton GLT is a product with a low brittle point of -51°C (-59°F) [48]. Tecnoflon for containing a stable fluorinated amide plasticizer reportedly exhibits improved low-temperature hardness, brittle point, and compression set without sacrificing physical properties [66]. Low-temperature characteristics of selected fluorocarbon elastomers are listed in Table 5.13 [9]. 

Fluoropolymer elastomers (or Viton, a registered trademark of the DuPont Performance Elastomer LLC) consist of hexafluoropropylene (HFP), vinylidene fluoride (VDF), and tetrafluoroethylene. The 3M Corporation uses the trade name Fluorel. The structures of each of these monomers are shown in Figure 8.14. The fluorine content of these terpolymers is typically around 70% for Viton. Four basic types of this material are shown in Table 8.8 however, Viton Extreme comprises more types. 

So for this particular elastomer, which happens to be a compound of DuPont s fluorinated copolymer known as Viton A, an O-ring squeezed 23 at room temperature cannot possibly seal below 230 K unless something is built into the flange to maintain force on the O-ring during and after cooldown. 

Some fluorinated polymers which show exceptional thermal stability and chemical inertness are Kel-F elastomers, made of a copolymer of chlorotrifluoroethylene-vinylidene fluoride C1CF=CF2/ CH2=CF2, and Viton, a copolymer of hexafluoropropylene and vinylidene fluoride CF2=CF—CF3/ CH2=CF2. 

Fluorinated elastomers are usually looked upon as being best equipped to withstand these conditions. The level of resistance can depend on the degree of fluorination of the backbone of the elastomer and the detaUs of the compounding used. Advances in steam resistance have recently been made with the introduction of high-fluorine peroxide-curable Viton GF and also peroxide-curable TFE/P Aflas 150P. 

Poly(VDF-co-CTFE) copolymers are crosslinked more easily in the presence of monoamines than poly(VDF-co-HFP) copolymers are, because HF ehmination should proceed more readily with tertiary fluorine than with the difluoromethylene group [20]. Hence, dehydrofluorination proceeds at a much lower rate with Viton-A than with Kel-F elastomer. 

Both (A) and (C) curves indicate a final exothermic reaction initiated in the vicinity of 285 °C, whereas the elastomer cured by Diak No3 shows some reaction as low as 200 °C. In contrast, the untreated Viton A-HV starts to decompose from 430 °C. Hence, vulcanization results in a decrease of the thermal stability of fluorinated elastomer. 

Some fluoropolymers prepared by DT with iodo-compounds have already been commercialized such as Daiel, Viton, and Technoflon. Such fluoroelastomers may find applications in high technology such as in O-rings, gaskets, hoses, transportation, medical devices, and electronics. The control of the architecture and functionality of the polymer chains makes possible the preparation of peroxide curable fiuoroelastomer with improved properties as well as the development of advanced fluorinated thermoplastic elastomers. Another application of functional fluoropolymers prepared by DT with iodo-compounds is the preparation of membranes for fuel cells. 

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