The effect of accelerator contents on the vulcanizate structures of SSBR/silica vulcanizates

Physical properties of rubber compounds are affected by the filler–rubber interaction, filler dispersion in the rubber matrix, and cross-link structure formed during vulcanization. In particular, the cross-link structure is closely related to the physical properties of vulcanizates and has been analyzed using the swelling test and Flory-Rehner equation. However, the relationship between the structure and physical properties of vulcanizates cannot be explained by the cross-link density obtained using these methods. The cross-link density obtained from the swelling test is a complex result of the filler–rubber interaction occurring during the compounding as well as the chemical cross-link structure formed by sulfur during the vulcanization. Moreover, the rubber vulcanizates that use silica need to be separately analyzed for each factor as its physical properties are affected more by the filler–rubber interaction than by carbon black. Therefore, this study determines the factors that contribute to the total cross-link density of vulcanizates into chemical cross-link density and filler–rubber interaction via quantitative analysis using the swelling test results and Flory-Rehner and Kraus equations. The vulcanizates used for the analysis were carbon black-filled and silica-filled non-functionalized SSBR compounds with varying cure accelerator for each filler loading. Their chemical cross-link density was measured and the effect of the filler–rubber interactions on their mechanical and dynamic viscoelastic properties was investigated. Furthermore, the relationship between the structure and physical properties of rubber vulcanizates was elucidated.