Styrene-butadiene rubber oxidative degradation

Other polymers used in the PSA industry include synthetic polyisoprenes and polybutadienes, styrene-butadiene rubbers, butadiene-acrylonitrile rubbers, polychloroprenes, and some polyisobutylenes. With the exception of pure polyisobutylenes, these polymer backbones retain some unsaturation, which makes them susceptible to oxidation and UV degradation. The rubbers require compounding with tackifiers and, if desired, plasticizers or oils to make them tacky. To improve performance and to make them more processible, diene-based polymers are typically compounded with additional stabilizers, chemical crosslinkers, and solvents for coating. Emulsion polymerized styrene butadiene rubbers (SBRs) are a common basis for PSA formulation [121]. The tackified SBR PSAs show improved cohesive strength as the Mooney viscosity and percent bound styrene in the rubber increases. The peel performance typically is best with 24—40% bound styrene in the rubber. To increase adhesion to polar surfaces, carboxylated SBRs have been used for PSA formulation. Blends of SBR and natural rubber are commonly used to improve long-term stability of the adhesives. 

He, S.-J., Wang, Y.-Q., Xi, M.-M., Lin, J., Xue, Y., Zhang, L.-Q. Prevention of oxide aging acceleration by nano-dispersed clay in styrene-butadiene rubber matrix. Polym. Degrad. Stab. 98, 1773-1779 (2013)... 

First, the stability of these polymer materials is very important for their practical use and processing. Assessment of surface chemical modification of rubber after aging treatment is, by example, primordial for pneumatic manufacturing. Similar to conventional methods, LA-MS is allowed to evaluate and follow the oxidation effects on model polymers such as polybutadiene (PB), polystyrene (PS), and styrene butadiene rubber (SBR) by both detection and identification of the degradation products. The thermooxidative stability of SBR has been then investigated. 

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]. 

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. 

The rubber-modified aromatic polymeric materials, for example, high-impact polystyrene (HIPS) and acrylonitrile-butadiene-styrene (ABS) are the least stable because of the rapid photooxidation of the rubber component, which sensitizes the polymer to further oxidation. Diene-based rubbers are also susceptible to degradation by ozone, which causes chain scission of the main-chain... 

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. 

---