Cure Systems for Butyl and Halobutyl Rubber

Isobutylene-based elastomers include butyl rubber, the copolymer of isobutylene and isoprene, halogenated butyl rubber, star-branched versions of these polymers and the terpolymer isobutylene-para-methylene styrene-bromo-para-methyl styrene (BIMS). Anumber of reviews on isobutylene-based elastomers are available (395, a.20, a.21). 

Polyisobutylene and butyl rubber have the good chemical resistance expected of saturated hydrocarbons. Oxidative degradation is slow and the material may be further protected by antioxidants, for example hindered phenols. 

In butyl rubber, the hydrocarbon group positioned alpha to the C-C double bond permits vulcanisation into a crosslinked network with sulfur and organic accelerators (408). The low degree of unsaturation requires the use of ultra accelerators, such as thiuram or dithiocarbamate. Phenolic resins, bisazoformates (a.22), and quinone derivatives can also be employed. Vulcanisation introduces a chemical crosslink every 250-carbon atoms along the polymer chain, producing a molecular network. The number of sulfur atoms per crosslink is between one and four or more (a.23). 

Butyl mbber is used in tyre tube applications among others. A typical formulation (mix 01) is shown in Table 22. The performance needs for inner tubes are  

The cure data are shown in Table 23. The data presented clearly show that Perkalink 900 does not influence the processing characteristics. Although a longer T90 seems to be negative, raising the temperature by 5 or 10 °C will neutralise this effect with the additional advantage of higher cure rate and stabilisation of tan delta characteristics. 

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