Various ways to reduce zinc oxide levels in S-SBR rubber compounds

Because of environmental concerns, the zinc content in rubber compounds has come under scrutiny. The research described in this article encompasses zinc-oxide, various zinc-complexes and alternative metal oxides as activators for sulphur vulcanisation. Regarding zinc complexes, it can be concluded that zinc- m-glycerolate is a good substitute for ZnO as activator for sulphur vulcanisation in s-SBR rubber, without detrimental effects on the cure characteristics. Of particular interest is also the positive effect of CaO and MgO in s-SBR, while BaO, Cu(II)O and BeO hardly show any activation. The present article also reports on the application of a novel activator for sulphur vulcanisation: ZnClay. Results with s-SBR rubber demonstrate, that this ZnClay can substitute conventional ZnO, retaining the curing and physical properties of the rubber products, while significantly reducing the environmental impact. A reduction of the zinc concentration with a factor 10 to 20 can be realised. Model Compound Vulcanisation studies are used to gain insight into the mechanism of this activator