The influence of silane sulfur and carbon rank on processing of a silica reinforced tyre tread compound

The effect of the sulfur rank (4-0) and of the carbon rank (2-10) of equivalents of bis(triethoxysilylpropyl)tetrasulphide TESPT as coupling agents for silica-reinforced tire tread compounds, is the subject of this study. The coupling agents are added in quantities equimolar to TESPT. Sulfur correction for lower sulfur ranks than TESPT is performed either in the final mixing step or in the first mixing step in an internal mixer.

Without sulfur correction the silanes studied show a marked difference in processing as well as in the final properties of the rubber. When sulfur correction is made in the final mix together with the addition of vulcanization ingredients, all sulfur-containing silanes behave more like TESPT. The disulphide (TESPD) shows final properties similar to those of TESPT; the mixing behavior shows improved scorch safety. This is lost when sulfur correction is applied in the first mix.

Sulfur-free silanes do not react on sulfur correction during processing and show only a slight improvement in mechanical properties. A silane without sulfur, having a carbon rank of 10 (DTES) shows the best processing, although final mechanical properties are inferior to TESPT.