Ozone attack butadiene acrylonitrile

Acrylonitrile butadiene rubber is susceptible to ozone attack, and therefore suitable anti-ozonants and/or waxes need to be added. Acrylonitrile butadiene rubber /EPDM blends (at 70/30 or 80/20 ratio) bave a better ozone resistance than NBR alone. 

It is proposed that this is due to attack of carbonyl oxides, in their biradical form, on the rubber double bonds. Typical diene rubbers (polyisoprene and polybutadiene) have rate constants several orders of magnitude greater than polymers having a saturated backbone (polyolefins). Other unsaturated elastomers having high reaction rates with ozone include styrene-butadiene (SBR) and acrylonitrile-butadiene (NBR) rubbers. As an example, Polychloroprene (CR) is less reactive than other diene rubbers, and it is therefore inherently more resistant to attack by ozone. 

The natural rubber does not generally exhibit all the desired properties for use in the rubber industry. Thus, it is possible to obtain better mechanical and physical properties at a lower cost by blending natural rubber with synthetic rubbers. Normally, natural rubber is deteriorated by ozone and thermal attacks due to its highly unsaturated backbone, and it also shows low oil and chemical resistances due to its non-polarity. However, these properties can be achieved by blending it with low unsaturated ethylene propylene diene monomer rubber, styrene butadiene rubber, carboxylate styrene butadiene rubber, nitrile butadiene rubber, chloroprene rubber, chlorosulfonated polyethylene rubber, and acrylonitrile butadiene rubber. 

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