Nitrile rubber general properties

PVC can be chlorinated (CPVC) and be alloyed with other polymers like ABS, acrylics, polyurethanes, and nitrile rubbers to improve its impact resistance, heat deflection, and processability. Although these vinyls differ in having literally thousands of varying compositions and properties, there are certain general characteristics that are common to nearly all these plastics. Most materials based on vinyls are inherently TP and heat sealable. The exceptions are the products that have been purposely compounded with TSs or crosslinking agents are used. 

These are generally manufactured by the emulsion copolymerisation process. The commercially available nitrile rubbers differ from one another in three aspects acrylonitrile content, polymerisation temperature and mooney viscosity. The content of acrylonitrile has a profound effect on the properties of vulcanised nitrile rubber, influencing its resistance to oils and fuels. 

Small nitrile-rubber inclusions in epoxy resin electrical en-capsulants have been examined in both amine (29-31) and acid (32) epoxy cures, in filled and unfilled systems. The value of rubber inclusion in a boron trlfluorlde/amine complex epoxy cure has also been demonstrated (33), where elevated-temperature, high-humldlty testing showed electrical properties retention to be better than a comparable system cured with dodecenylsucclnic anhydride. Rubber benefits low-temperature properties specifically and thermocycling in general. It affects high temperature insulation properties negatively therefore, the amount of rubber incorporated must be judiciously chosen. 

Oil Resistance The primary property of nitrile rubber is oil resistance and it is this factor, in conjimction with its excellent physical properties, which account for much of its commercial use. Oils generally attack rubbers by causing them to swell. 

A nitrile masterbatch, see Table 8.3, was used in all experiments pertaining to nitrile rubbers. Hycar 1042 (Zeon Chemicals) is a general purpose NBR (acrylonitrile content is 33%) with good processing characteristics and high physical properties. 

Whilst the peroxide-initiated emulsion polymerized polybutadiene had disappointing properties it was found in 1929 that copolymerization of butadiene with styrene and in 1930 with acrylonitrile led to the production of interesting materials. The butadiene-styrene rubber. Buna S, was potentially a general purpose rubber but at that time not competitive with natural rubber. On the other hand the butadiene-acrylonitrile rubber. Buna N, now commonly known as nitrile rubber had certain properties such as oil resistance not shown by natural rubber and commercial production was started about 1935. Commercial production of butadiene-styrene rubber did not commence until 1937 and many things were to happen before it became the world s most used rubber. 

Elastomer epoxies generally contain nitrile rubber as the elastomeric component. This system is also referred to as a modified or toughened epoxy. One of the applications of widest use is in films and tapes. Elastomer epoxies cure at low pressures and low temperatures over a short time interval. This is achieved by adding a catalyst to the adhesive formulation. Bond strengths of elastomer epoxies are lower than those of nylon epoxies. However, the major advantage of elastomer epoxies is their sub-zero peel strengths, which do not decrease as fast as those of nylon epoxies. In addition, the moisture resistance of elastomer epoxies is better than that of nylon epoxies but not as good as that of vinyl-phenolics or nitrile-phenolics. Limitations to the use of elastomer epoxies include poor water immersion resistance and poor properties when exposed to marine conditions. 

The structure and vulcanisation mechanisms of carboxylated rubbers in general are discussed, and results are presented of a study of the vulcanisation of carboxylated nitrile rubber using four different curing systems. The crosslink density, tensile and dynamic mechanical properties, stress relaxation and tear strength of vulcanised samples were investigated. 22 refs. 

The most common adhesive system used for bonding continuous fibers and fabrics to rubber is resorcinol-formaldehyde latex (RFL) system. In general, RFL system is a water-based material. Different lattices including nitrile and SBR are used as the latex for the adhesive system. 2-Vinylpyridine-butadiene-styrene is the common latex used in the adhesive recipe. RFL system is widely being used in tires, diaphragms, power transmission belts, hoses, and conveyor belts because of its dynamic properties, adhesion, heat resistance, and the capacity to bond a wide range of fabrics and mbbers. 

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