Fluoro-elastomers

The industrial relevance of peroxide-curing of elastomers is by far larger for main-chain saturated elastomers, such as silicone elastomers, acrylic elastomers, fluoro elastomers... 

Property Butyl/halobutyl (isobutylene- isoprene copolymer) N atur al/Isoprene (cis-1,4-polyisoprene) Nitrile (butadiene- Sdicone Neoprene acrylonitrile (polydi-(polycbloroprene) copolymer) metbysiloxane) Fluoro- elastomers (fluoro- rubber) Uretbane (polyesterisocyanate) EPDM (etbylene Butadiene propylenediene (cis-polybuta-monomer) diene) ... 

Logothetis [62] describes the use of triazine accelerators in the vulcanization of nitrile and fluoro elastomers. The triazine is more effective than the thiazole accelerators and produces highly reversion-resistant vulcanizates. 

Saturated hydrocarbons (waxes), fatty acids, metal soaps, fatty acid amides and esters (primarily Cig-Cis) act as internal lubricants, fluoro elastomers as external lubricants. Many other polymer additives, e.g. antistatic agents, antifogs, antioxidants, UV stabilisers, etc., act as lubricants in the barrel of the extruder once they are in the liquid form. 

Sicka, R. W. Mitchell, G. B. "Phosphonitri1ic Fluoro-elastomer Coated Fabrics For Collapsible Fuel Storage Tanks", The Firestone Tire and Rubber Company, Akron,... 

Therefore, at room temperature Fluoro-PSB-II a thermoplastic elastomer with a soft polymer phase (fluorinated block) and a hard phase (PS-block), similar to the parental polystyrene-6-polybutadiene block copolymer. Depending on the relative volume fraction of both components and the continuity of the phases, the resulting bulk material is rubbery or a high-impact solid. 

Viton Fluoro-elastomer Resistant to degradation by fuel, temperature to 500°F (260°C) and compression Fuel line housings metering or needle valves... 

Bhowmick and co-workers [168] investigated the bulk and surface modification of ethylene propylene diene monomer (EPDM) rubber and fluoro-elastomer by electron beam irradiation. The structure of the modified elastomers was analysed with the help of IR spectroscopy and XPS. The gel content, surface energy, friction coefficient and dynamic mechanical properties of bulk modified fluoro-elastomers and the surface-modified EPDMs were also measured. The resultant properties of the modified EPDM were correlated with the structural alterations. 

Some typical elastomers are natural rubber, which is gathered from trees, SBR rubber, which is used a lot in motorcar tires, neoprene, as in wet suits and oil seals, EPDM, a general purpose rubber, butyl, a heat-resistant rubber with the ability to keep the air in car tires, nitrile for oil seals, silicones for heat resistance, fluoro-elastomers for chemical resistance, and last but not least, polyurethanes, which cover a number of the above fields. Table 1.1 shows some of the advantages of castable polyurethanes over conventional rubbers. 

The introduction of fluorine into the elastomeric macromolecule generally produces materials exhibiting an improved retention of properties at high temperatures, an improved 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. 

As a result of its saturated polymer backbone, EPDM is more resistant to oxygen, ozone, UV and heat than the low-cost commodity polydiene rubbers, such as natural rubber (NR), polybutadiene rubber (BR) and styrene-butadiene rubber (SBR). Therefore, the main use of EPD(M) is in outdoor applications, such as automotive sealing systems, window seals and roof sheeting, and in under-the-hood applications, such as coolant hoses. The main drawback of EPDM is its poor resistance to swelling in apolar fluids such as oil, making it inferior to high-performance elastomers, such as fluoro, acrylate and silicone elastomers in that respect. Over the last decade thermoplastic vulcanisates, produced via dynamic vulcanisation of blends of polypropylene (PP) and EPDM, have been commercialised, combining thermoplastic processability with rubber elasticity [8, 9]. 

Solid-state 13C NMR has been used to identify elastomers in binary blends of chloroprene (CR) and NR, CR and CSM, NR and CSM, and SBR and acrylonitrile-butadiene rubber (NBR). The type of NBR can be determined by identifying the sequences of acrylonitrile and butadiene. The tertiary blend of NR/SBR/BR was also studied [49]. High-temperature 13C solid-state NMR identified ethylene-propylene diene terpolymer (EPDM) and fluoro and nitrile rubbers [50]. 

Silicone rubber offers a set of unique properties to the market, which cannot be obtained by other elastomers. The Si-0 backbone provides excellent thermal stability and, with no unsaturation in the backbone, outstanding ozone and oxidative stability. The very low glass transition temperature, combined with the absence of low-temperature crystallization, puts silicones among the materials of choice for low-temperature performance. The fluoro-substituted versions provide solvent, fuel, and oil resistance along with the above-mentioned stability advantages inherent with the silicone backbone. 

Tatemoto M (1979) Recent studies on fluoro-elastomers of vinylidene fluoride . First regular meeting of soviet-japanese fluorine chemists, Tokyo 15-16 Feb. 

Perfluoropyridine (3.0 g, 17.8 mmol), anhyd KF (3.0 g, 55.9 mmol), and sulfolane (15 mL) were introduced into a Carius tube (ca. 100 mL) and hexafluoropropene (5.0 g, 33.3 mmol) was introduced from a vacuum system. The tube was sealed under vacuum and heated for 12 h at 130 C. It was then cooled in liquid air and opened to a vacuum system. The volatile components were fractionated in the vacuum system to give hexafluoropropene (0.5 g) and higher boiling material (8.0 g). The latter was separated by GC (silicone elastomer on Celite) to give derivatives of hexafluoropropene (2.7 g), perfluoropyridine (0.3 g), and per-fluoro(4-isopropylpyridine) yield 4.8 g (94%). 

Seal compatibility Elastomeric seals are essential parts of engine design for a number of reasons, including preventing leakage of oil from the sump. Due to good thermal stability and resistance to oxidation, fluoro-elastomers are commonly used... 

Fluoro-elastomers dispersed in a resin, e.g., PI, PAI, PSF, PEI, PES, PEEK, PPS, PPE, etc. moldings flexible, elastic, self-lubricating, having excellent chemical and thermal resistance Movak et al., 1994... 

Sheets of Class SC (caulking compounds) elastomers, 0.16 cm thick, were prepared by casting the caulks in open molds, 15 cm X 2.5 cm. The bottom of the mold was covered with a thin sheet of Mylar, which had been coated with a silicone and then a fluoro-... 

Free diamines, used for cross-linking, are too reactive and can cause premature gelation. It is common practice, therefore, to add these diamine compounds in the form of carbamates, like ethylenediamine carbamate or hexamethylene diamine carbamate. The above fluoro elastomers exhibit good resistance to chemicals and maintain useful properties from —50 to -i-300°C. 

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