Nitrile rubber degradation resistance

Although, the heat resistance of NBR is directly related to the increase in acrylonitrile content (ACN) of the elastomer, the presence of double bond in the polymer backbone makes it susceptible to heat, ozone, and light. Therefore, several strategies have been adopted to modify the nitrile rubber by physical and chemical methods in order to improve its properties and degradation behavior. The physical modification involves the mechanical blending of NBR with other polymers or chemical ingredients to achieve the desired set of properties. The chemical modifications, on the other hand, include chemical reactions, which impart structural changes in the polymer chain. 

The hydrogenated products are nitrile rubber, with good heat resistance, and styrene-butadiene-styrene copolymer, with high tensile strength, better permeability and degradation resistance. 

Hydrogenation is an important method of chemical modification of elastomers. Because of the absence of carbon-carbon unsaturation, hydrogenated elastomers have good resistance to oxidative and thermal degradation, improved weatherability and good resistance towards chemicals and fluids [5-7]. Nitrile rubber (NBR) is a specialty rubber, and because of its oil resistance properties, it has been used in oil-wells and the automotive industry. Hydrogenation of NBR has been studied extensively because of its technological importance [16-19]. 

Plasticizer migration from the vinyl part into the adhesive bond line can degrade the strength of the joint. Adhesives must be tested for their ability to resist the plasticizer. PVC can be made with a variety of plasticizers. An adhesive suitable for a certain flexible PVC formulation may not be compatible with a PVC from another supplier. Nitrile rubber adhesives have been found to be very resistant to plasticizers and are often the preferred adhesive for flexible PVC films. However, certain epoxy adhesive formulations have also been found to provide excellent adhesion to flexible PVC substrates. Several such starting formulations are presented in Table 16.7. A comparison of the performance of several classes of adhesive when bonding PVC to itself and to various other materials is given in Table 16.15. 

Synthetic mbbers are characterized by good thermal stability due to its stmcture, for this reason the rubbers have very important applications. The nitrile rubber (NBR) is a polymer used in applications requiring resistance to high temperatures of oil. Balachandran et al. reported behavior NBR-nanoclay nanocomposites, showing that the temperature at which degradation occurs is increased by adding the nanoclays [74]. 

The more serious cause of deterioration in rubbers is its reaction with atmospheric oxygen. This is possible because rubber is a diene polymer and some, such as natural rubber, EPDM, SBR, nitrile rubber, and butyl rubber, have olefinic double bonds in their structure. Much research work is being done on the oxidative degradation of unvulcanized rubbers, but this is not relevant to the resistance of vulcanized rubbers in storage or in service as their aging behaviors differ widely. Unvulcanized rubber compound has to be vulcanized in order to produce usable products. The nature of the cross-link produced varies considerably, and this can affect the balance of chemical and particularly of physical properties of the vulcanizates. 

The copolyesters resistance to nonoxidizing acids, some aliphatic hydrocarbons, aromatic fuels, hot oils, and hydraulic fluids ranges from good to excellent. Thus, they compete with such rubbers as nitriles, epichlorohydrins, and acrylates. However, hot polar materials, strong mineral acids and bases, and chlorinated solvents and creosols degrade the copolyesters. Their weather resistance is low but can be improved considerably, with UV stabilizers and carbon-black additives. 

Problem 5-18 (Level 3) Parent et al. have studied the selective hydrogenation of C=C bonds in nitrUe-butadiene rubber (NBR) to produce hydrogenated nitrile-butadiene rubber (HNBR), which has superior resistance to thermal and chemical degradation. To obtain the desired product, the rate of hydrogenation of C=C bonds must be much higher than the rate at which the nitrile group (- C=N) is hydrogenated. 

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