Nitrile rubber solvent resistance

EPDM), a synthetic rubber with a typical Shore A hardness of 50 +5%. Seals for thin-wall piping and ductwork are made of softer EPDM with a Shore A hardness of 40 +5%. This lower-durometer rubber makes it possible to effect a seal at lower torque, thereby avoiding deformation of the piping or ducts. Some seals are made of virgin nitrile rubber for resistance to oils, gasoline, and solvents, as well as synthetic silicon rubber for steam applications. 

Acrylonitrile (AN), C H N, first became an important polymeric building block in the 1940s. Although it had been discovered in 1893 (1), its unique properties were not realized until the development of nitrile mbbers during World War II (see Elastomers, synthetic, nitrile rubber) and the discovery of solvents for the homopolymer with resultant fiber appHcations (see Fibers, acrylic) for textiles and carbon fibers. As a comonomer, acrylonitrile (qv) contributes hardness, rigidity, solvent and light resistance, gas impermeabiUty, and the abiUty to orient. These properties have led to many copolymer apphcation developments since 1950. 

Poly(butadiene- (9-acrylonitrile) [9008-18-3] NBR (64), is another commercially significant random copolymer. This mbber is manufactured by free-radical emulsion polymerization. Important producers include Copolymer Rubber and Chemical (Nysyn), B. F. Goodrich (Hycar), Goodyear (Chemigum), and Uninoyal (Paracdl). The total U.S. production of nitrile mbber (NBR) in 1990 was 95.6 t (65). The most important property of NBR mbber is its oil resistance. It is used in oil well parts, fuels, oil, and solvents (64) (see Elastomers, synthetic— nitrile rubber). 

Nitrile Rubber (NBR). This is the most solvent-resistant of the synthetic elastomers, except for Thiokol, which, however, has rather severe limitations. NBR was developed both in Germany and the United States by private industry prior to World War II. It is a copolymer of butadiene, CH2=CH—CH=CH2, and acrylonitrile, CH2=CHCN, corresponding to the molecular stmcture shown in Table 1. 

Elastomers, syntpietic-nitrile rubber). It is the nitrile group, —C=N, that confers oil resistance to this polymer, and the nitrile content can vary from 10 to 40%, leading to increasing solvent resistance. 

Nitrile rubbers have high resistance to oils and organic solvents, and, although their mechanical properties are not as good as those of natural rubber, they are subject to much less deterioration in the presence of oils and solvents. They are not resistant to ozone attack. 

As the acrylonitrile content in nitrile rubber increases, so does the resistance to nonpolar solvents. 

Although a large number of synthetic elastomers are now available, natural rubber must still be regarded as the standard elastomer because of the excellently balanced combination of desirable qualities. The most important synthetic elastomer is styrene-butadiene rubber (SBR), which is used predominantly for tires when reinforced with carbon black. Nitrile rubber (NR) is a raudom copolymer of acrylonitrile and butadiene and is used when an elastomer is required that is resistant to swelling in organic solvents. 

Except for the monomers used, the production of NBRs is quite similar to that described for the SBRs. The NBR family is sometimes referred to as the nitrile rubbers. The acrylonilnle-buiadiene ratios cover a wide range from 15 85 to 50.50. NBRs are noted for their solvent resistance, increasing wiih the acrylonitrile content Thus, they are used for gaskets and oil and gasoline hoses, solvent-resistant electrical insulation, and Ibod-wrnpping films. Nitrile lattices also are used in treating fabrics for dry-cleaning durability. Because the NBRs become quite inflexible (stiff) at low temperatures (actually brittle at about -20 C). they arc blended with polyvinyl chloride for some applications. 

Acrylonitrile-Butadiene Elastomers. These polymers, the so-called nitrile rubbers , are used dissolved in ketone or other highly polar solvents. When they are compounded with thermosetting phenolic resins it is possible to obtain good resistance to elevated temperatures. 

Nitrile rubber was invented at about the same time as SBR in the German program to find substitutes for natural rubber.56 These rubbers are copolymers of acrylonitrile-butadiene, containing from 15 to 40 percent acrylonitrile. The major applications for this material are in areas requiring oil and solvent resistance. The estimated worldwide consumption in 2003 was 303,000 metric tons.57... 

During the last 15 years several companies have developed hydrogenated grades of nitrile rubber to both improve its thermal stability and solvent resistance. Although the hydrogenation of a poly diene backbone was done as early as the 1920s, real commercial products with acrylonitrile were not introduced until the mid-1980s.59... 

The latexes upon which this industry developed were natural rubber and polychloroprene for solvent resistance. However, technology is advancing to permit penetration of carboxylated nitrile latex for optimized solvent resistance and tougher abrasion resistance. Among the competition to latexes in this field are poly(vinyl chloride) plastisols. As technology develops in producing small particle size latexes from polymers whose synthesis is loo water-sensitive for emulsion polymerization, the dipped goods industry will quickly convert to their utilization from the solvent-based cements of these polymers now employed Prime candidates include butyl rubber, EPDM, hypalon, and vlton. 

BL) High-strength, film-forming, nitrile rubber latexes and rubbers and carboxylated polymers characterized by exceptional oil, solvent, and abrasion resistance. 

PERSONAL PROTECTION wear impervious protective clothing, including boots, solvent-resistant gloves, lab coat, apron or coveralls nitrile and neoprene rubbers or polyvinyl alcohol is recommended as protective materials wear splash-proof chemical goggles when working with liquid enclose operations and use local exhaust ventilation at the site of chemical... 

Lewis and co-workers (42) developed improved powder coatings with nitrile rubber-modification of an appropriate epoxy base (solid resin admixture) cured with an imidazoline-accelerated modified phenolic type hardener. Model coatings ground to 55 pm particle size, electrostatically applied to metals, cured 10 170°C, gave excellent therraocycling results as well as retained resistance to solvent attack. Elastomer-modified epoxy powder coatings have been covered extensively by Gelbel, Romanchick and Sohn in Chapter 5 of this volume. 

A large family of artificial rubbers related to natural rubber is now produced. One of the earliest examples was obtained by the polymerisation of butadiene in the presence of sodium (Na), to give buna (Butadiene + Na) rubber. Two other widely used rubbers are neoprene (Scheme 6.12a), a rubber resistant to organic solvents, and nitrile rubber (Scheme 6.12b), which is a copolymer of butadiene (CH2=CH—CH=CH2) and propenenitrile (CH2=CH-CN). 

Nitrile rubbers (vulcanized) are used almost invariably because of their resistance to hydrocarbon oil and gasoline. They are, however, swollen by aromatic hydrocarbons and polar solvents such as chlorinated hydrocarbons, esters, and ketones. 

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