Synergistic effects in silica-reinforced natural rubber compounds compatibilised by ENR in combination with different silane coupling agent types

Bis-(3-triethoxysilyl-propyl)tetrasulfide (tespt),3-mercaptopropyl-di(tridecan-1-oxy-13penta(ethyleneoxide)) ethoxysilane (vp si-363™) and 3-octanoyl-thio-propyltriethoxysilane (nxt™) are comparatively studied at varying amounts from 2 to 5 wt% relative to the silica,in combination with 7.5 phr of epoxidised natural rubber (enr) with 51 mol% of epoxide (enr51),as compatibilisers for silica-filled nr compounds. the compounds with enr and vp si-363 or nxt show a lower mooney viscosity and reduced bound rubber contents and moduli at 100% and 300% elongations when compared to the one with tespt. the presence of enr51 at 7.5 phr already effectively reduces the filler-filler interactions. the addition of silane on top of the enr has only little influence on mooney viscosity and payne effect,but clearly enhances filler-rubber interactions as indicated by an increased chemically bound rubber content. the tensile properties of the silica-filled nr vulcanisates are increased with increasing silane contents,in which state-of-the-art tespt still provides better properties than the other silanes,while vp si-363 and nxt give more or less the same properties. at a fixed silane content of 4 wt% relative to silica and 7.5 phr of enr51,sulphur compensation added into the compounds by taking the mix with optimal content of tespt as reference,enhances the tensile modulus and strength. in the presence of enr,the dynamic mechanical properties of the silica-filled nr compounds are influenced by the glass transition temperature of the enr. with respect to tyre rolling resistance,the use of tespt provides the lowest loss tangent at 60°c.