New silane coupling agents for silica tire tread compounds

Effectiveness of four new silane coupling agents in solution styrene butadiene rubber–based silica tire tread compounds were evaluated with respect to two commercial silane coupling agents. The new silane coupling agents investigated were 1-[3-(octanoylthio) propyl]-1,1,3,3,3-pentaethoxy-1,3-disilapropane (S1), bis[3-(octanoylthio)-1-propyl]-diethoxysilane (S2), 5-(triethoxysilylpropylthia)-2-potassium-1,3,4-thiadiazolate (S3) and 2,5-(triethoxysilylpropylthia)-1,3,4-thiadiazole (S4), and the two commercial silanes used for the comparison were bis(triethoxysilylpropyl) tetrasulphide (Si69) and 3-octanoylthio-1-propyltriethoxysilane (NXT). The chemical structure of S1 and S2 silanes was based on the NXT silane. S3 is a monofunctional silane, whereas S4 is a bifunctional silane based on the chemical structure of S3. The effectiveness of the coupling agents were found to be varying for different properties of the rubber compounds. The S3 and S4 silane compounds were having shorter cure time and higher maximum torque values compared with other compounds; however, the tensile strength and the tanδ values indicative of tire performance were lower than that of the other silane compounds. The NXT, S1 and S2 silane compounds showed higher tanδ at 0°C and lower tanδ at 60°C, compared with the other compounds, indicative of improved wet skid resistance and lowered rolling resistance of these compounds. The Si69 compound showed higher tensile properties and lower abrasion when compared with the other compounds; however, the tanδ values for the tire performance were slightly lower to the NXT, S1 and S2 silane compounds.