Surface modification of sol–gel derived nano zinc oxide (ZnO) and the study of its effect on the properties of styrene–butadiene rubber (SBR) nanocomposites

Very recently, nano zinc oxide (ZnO) has been successfully introduced as a cure activator for the reduction of ZnO level in the rubber industry. The purpose of the present work is to examine the appropriateness of surface-modified nano ZnO in the vulcanization of styrene–butadiene rubber (SBR). In the experimental part, the surface of nano ZnO is modified by stearic acid and bis[3-(triethoxysilyl)propyl]tetrasulfide (Si-69). Si-69-treated nano ZnO causes considerable enhancement in many properties such as maximum rheometric torque, modulus, tensile strength, elongation at break, cross-linking degree of SBR nanocomposite in comparison to conventional ZnO and unmodified or stearic acid-treated nano ZnO. Thermogravimetric analysis (TGA) reveals that Si-69-treated nano ZnO imposes better thermal stability than untreated or stearic acid-treated nano ZnO in the SBR vulcanizates. Morphological study indicates uniform dispersion of Si-69-treated nano ZnO within the SBR matrix and this fact accounts for better mechanical and thermal properties of SBR nanocomposite in the presence of Si-69-modified nano ZnO. This study concludes that Si-69-modified nano ZnO can be effectively applied as cure activator in place of nano ZnO to reduce the ZnO level in SBR compounds. This will lead to both economic advantages and environmental safety in the rubber industry.