Properties, Processing, and Applications of Fluoroelastomers

The introduction of fluorine into the elastomeric macromolecule generally produces materials exhibiting an improved retention of properties at high temperatures, reduced flexibility at low temperatures, and an improved resistance to solvents. Essentially, there are two groups of fluoroelastomers fluoro-inorganic elastomers and fluorocarbon (or fluorohydrocarbon) elastomers. 

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Peroxidic cure systems are applicable only to fluorocarbon elastomers with cure sites that can generate new stable bonds. Although peroxide-cured fluorocarbon elastomers have inferior heat resistance and compression set, compared with bisphenol cured types they develop excellent physical properties with little or no postcuring. Peroxide cured fluoroelastomers also provide superior resistance to steam, acids, and other aqueous solvents because they do not require metal oxide activators used in bisphenol cure systems. Their difficult processing was an obstacle to their wider use for years, but recent improvements in chemistry and polymerization are offering more opportunities for this class of elastomers [42]. 

The phosphazene fluoroelastomers can be compounded and processed to give an excellent balance of properties (Table 1) which make them suitable for a variety of applications which require the combination of fuel and oil resistance with a wide service temperature range ( ). Initial development work focused on demanding applications in aerospace, military, petrochemical and gas pipeline areas. The phosphazene fluoroelastomers are currently being used or evaluated in both military and commercial applications, and their continuing demand in these areas is now established. Some examples are shown in Figure 5 (21). 

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