Fluorine-containing rubbers

It is of interest to note that the main chain bonds in most common use (Si—O, C—C, and C—O) have very similar bond energies. It is also reasonable to conclude that those rubbers containing only C—C, C—O, C—H, and/or C—F bonds, even when cross-linked, would have good heat resistance under anaerobic conditions. Such a conclusion is borne out by the ethylene-propylene rubbers, the acrylic rubbers, fluorine-containing rubbers and the polyepichlorhydrins. 

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... 

Fluorine-containing rubbers were originally developed during the search for fluid-resisting elastomers which could be used over a wide temperature range. Much of the initial developmental work was a result of contracts placed by the US Army and Air Force. Whilst the eurrent commercial materials are very expensive compared with general purpose rubbers they find a number of both military and non-military applications, particularly in the area of seals and 0-rings. 

In attempts to further improve the stability of fluorine-containing elastomers Du Pont developed a polymer with no C—H groups. This material is a terpolymer of tetrafluoroethylene, perfluoro(methyl vinyl ether) and, in small amounts, a cure site monomer of undisclosed composition. Marketed as Kalrez in 1975 the polymer withstands air oxidation up to 290-315°C and has an extremely low volume swell in a wide range of solvents, properties unmatched by any other commercial fluoroelastomer. This rubber is, however, very expensive, about 20 times the cost of the FKM rubbers and quoted at 1500/kg in 1990, and production is only of the order of 1 t.p.a. In 1992 Du Pont offered a material costing about 75% as much as Kalrez and marketed as Zalak. Structurally, it differs mainly from Kalrez in the choice of cure-site monomer. 

Although we made no attempt to elucidate the mechanism of friction decreases in rubbers after surface fluorination, it seems to us that apart from the substitution of H atoms to F in the polymer macromolecule, which forms a fluoropolymer on the surface, there is another phenomenon that makes a significant contribution to the friction decreases, i.e., fluorination of carbon black, which is used in rubber recipes for reinforcement. It appears that when the carbon black in the surface of the rubber is fluorinated it produces a lubricating effect, followed by blooming on the surface of the treated rubber while it is under a friction load. So, in our opinion, two effects contribute to friction decrease of carbon-filled rubbers fluorination of the rubber macromolecules and fluorination of the carbon black rubbers that do not contain carbon black show a much smaller decrease in friction after XeF2 treatment. 

By adding new types of surfactants (not more than 1.2% by weight), nano-heterogenic systems with a very good specific surface of phase separation were formed. The data demonstrated the influence of the chemical composition of fluorine-containing surfactants on the properties of epoxy-rubber coatings, and are... 

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. 

Fluoroelastomers Fluorine-containing synthetic rubber with good chemical and heat resistance. Used in underhood applications such as fuel lines, oil and coolant seals, and fuel pumps, and as a flow additive for polyolefins. Also called Fluoro Rubber. 

Three polymers, listed in Table 26.6, were selected for further work in which the effect on ITV of fillers, antioxidants and UV absorbers was to be examined. The effect of fillers was explored in the fluorine containing copolymer, the silicone copolymer and polyethylene polyethylene was selected for antioxidant and UV absorber study because of the three it is the most susceptible to oxidation. These results showed that there was a general deterioration compared with pure polymers, although hydrated alumina showed some benefit in polyethylene and silicone rubbers. However such results were not general - alumina hydrate for example deteriorates the performance of fluorine copolymers. The following tables summarize these effects. (Tables 26.6, 26.7, 26.8). 

A definite inverse relationship exists between the thermal stability and radiation stability of rubbers. Thus, nitrile, polysiloxane, and fluorine-containing raw rubbers are the most thermally stable and the most unstable with respect to ionizing radiations. A significant influence on the radiation stability of cured rubbers is exerted by various three-dimensional structures formed during the process of vulcanization, as well as by the Ingredients (vulcanizing substances, fillers, softeners). Thus, sulfur and thiuram (free and bound) decelerate radiation structuring [69, 70], Carbon blacks participate in the formation of a space lattice under the action of y-radiation [61, 71-76],... 

Fluoroelastomers are fluorine containing hydrocarbon polymers with a saturated structure obtained by polymerizing fluorinated monomers such as vinylidene fluoride, hexafluoroprene, and tetrafluoroethylene. The result is a high performance rubber with exceptional resistance to oils and chemicals at elevated temperatures. 

Huoroelastomers are fluorine containing hydrocarbon polymers manufactured under various tradenames such as Viton by DuPont, Technoflon by Ausimont, and Fluorel by 3M. The fluoroelastomers provide excellent resistance to oils, fuels, lubricants, most mineral acids, many aliphatic and aromatic hydrocarbons (carbon tetrachloride, benzene, toluene, xylene) that act as solvents for rubbers, gasoline, naphtha, chlorinated solvents, and pesticides. 

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