The use of a silanised silica filler to reinforce and crosslink natural rubber

The availability of the coupling agent bis(3-triethoxysilylpropyl-)tetrasulphane (TESPT) has provided a better opportunity for using synthetic silicas to reinforce natural rubber. TESPT chemically adheres silica to rubber and also prevents silica from interfering with the reaction mechanism of sulphur-cure. Some rubber compounds were prepared by mixing a large amount of precipitated amorphous white silica with natural rubber. The silica surfaces were pretreated with TESPT and the filler was perfectly dispersed in the rubber. The rubber was cured primarily by using sulphur in TESPT and the cure was optimised by adding a sulphenamide accelerator and zinc oxide to the rubber. The need for the accelerator depended on the amount of silica incorporated into the rubber.