Styrene-butadiene rubber degradation resistance

Styrene-butadiene rubber, similar to natural rubber, is only slightly resistant to light attack and in particular to photo-oxidative degradation. In contrast to natural rubber, crosslinking is dominant [32]. 

Although natural rubber has satisfactory properties in many applications there are now many synthetic alternatives available. Natural rubber is rather prone to chemical degradation by ozone and has poor resistance to solvents. Synthetic rubbers are usually better in these respects. The most important use of rubbers is in motor vehicle tyres in which styrene-butadiene rubber (a random copolymer, SBR), is mainly used along with a variety of additives such as carbon black. This reinforces the rubber and improves the strength, stiffness and abrasion resistance. 

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

In other applications the pattern of evolution of styrene, butadiene and acrylonitrile as a function of temperature has provided a unique way for classifying different types of ABS. The loss of the antioxidant butylated hydroxytoluene (BHT) was also detected by MS preceding EVA copolymer degradation [165] BHT was identified at a concentration level of 20 ppm. Lehrle and co-workers [52] have described a successful controlled release system for the stabilisation of rubber by encapsulating efficient but rather mobile antioxidants to prevent loss from the host polymer. The performance of the controlled-release of the antioxidant BHT from alginate matrix particles was studied by means of DSC, TG and TG-MS. Polyisoprene rubber is more resistant to oxidation when protected in this way than by the equivalent concentration of unencapsulated antioxidant. 

Styrene-isoprene butadiene rubbers are manufactured with varying combinations of styrene, butadiene, and isoprene contents here, different isomers can be present in the isoprene. Degradation in these double bonds begins with cis-1,4 units, followed by trans-1,4 units, whereas 3,4 and 1,2 units degrade only slightly. Thus, more aging-resistant elastomers can be manufactured by the targeted use of poly-isoprene with 3,4 and 1,2 units. The styrene units are not subject to attack [797]. 

Most pressure-sensitive masscoats contain a blend of elastomers—natural rubber, reclaim and SBR—with tackifiers of low or medium molecular weight, antioxidants, etc. These are applied to the web-tape or label backing from solutions but the newer thermoplastic elastomers —block copolymers of styrene with is-oprene or butadiene—can be applied from melt. Where excellent color and resistance to light and oxidation are needed, the higher priced acrylic ester copolymers are preferred. Polyisobutylene, also resistant to ultraviolet degradation, is utilized for removable labels. 

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