Silica reinforement of natural rubber by sol-gel process in latex

Abstract

Beside carbon black, silica powder is the other important filler used to reinforce various colored rubber products. In order to improve the compatibility between silica particles and rubber phase, this work has focused on preparing an NR composite, reinforced by silica generated inside the NR matrix or ‘in situ’. The silica particle was formed by a sol-gel process of tetraethoxysilane (TEOS) dispersed in NR latex. The latex used was concentrated latex having 60% rubber content, and already contained water and ammonia, two ingredients needed for the sol-gel reaction. The conversion of TEOS to silica was close to 100% and the particles size was about 44 nm in diameter, determined by TEM. The silica particles scattered evenly in the rubber. A statistical analysis method, named ‘two-level factorial design’, was used to study the influence of the amount of TEOS, ammonia, and gelation time on the mechanical properties of the composite. Silica content as high as 19% was prepared successfully. The composite had a tensile modulus of 3.7 MPa and a tear strength value of 41 N/nm. It was also found that the composite containing in situ silica had a higher tensile modulus and tear strength than a composite that was prepared by conventionally mixing with silica power.