OPTIMIZATION OF RUBBER FORMULATION FOR SILICA-REINFORCED NATURAL RUBBER COMPOUNDS

Abstract

ABSTRACT The rubber formulation plays a significant role in the properties of NR compounds filled with silica. In this work, the influences of various silicas, silane coupling agents, and diphenylguanidine (DPG) on the properties of compounds and vulcanizates—that is, cure characteristics, Mooney viscosity, flocculation kinetics, bound rubber content, Payne effect, tan δ at 60°C, tensile properties, and tear properties—are investigated. The results demonstrate that compound viscosity and curing behavior, as well as vulcanizate properties of the silica-filled NR, are much improved by incorporating silane coupling agents. Bis-triethoxysilylpropyltetrasulfide clearly gives better overall properties than the disulfide-based silane bis-triethoxysilylpropyldisulfide, except for scorch safety. DPG acts as a synergist to sulfenamide primary accelerators, as well as activator for the silanization reaction. Highly dispersible (HD) silicas can significantly enhance the degree of dispersion and so lead to higher filler–rubber interaction. As a consequence, the HD silicas provide better dynamic and mechanical properties for filled NR vulcanizates compared with conventional counterparts. The optimal quantities of both silane coupling agent and DPG required in the formulation are correlated to the cetyl trimethylammonium bromide specific surface area of the silicas. Furthermore, the results reveal that the silica structure as characterized by the dibutylphthalate adsorption also strongly influences the reinforcing efficiency.