Natural rubber reinforced by in situ silica generated in rubber solution by sol-gel process

Abstract

In this study, the synthesis of in situ silica filled in natural rubber (NR) solution was investigated to find the optimum that produced high in situ silica content and good dispersion of silica particle. The effects of solvent, type of catalyst, catalyst concentration, mole ratio of tetraethoxysilane (TEOS) to water, reaction temperature and reaction time on in situ silica formation were investigated. The results indicated that the optimum condition produced high silica content (up to 41% by weight) in rubbery matrix obtained from the use of 0.1395 M n-hexylamine as the catalyst in tetrahydrofuran and the mole ratio of TEOS to water 1:2.7 under 50 oC for 7 days. Various properties, i.e., curing, mechanical, dynamic mechanical and thermal properties of composite materials were also investigated. The results indicated that the increasing in situ silica content affected to increase the cure time and improve the tensile properties of the composite. In comparison with commercial silica and calcium carbonate, the mechanical properties of the in situ silica composite material was better; however, it was still lower than mechanical properties of carbon black composite. The addition of coupling agent also improved the mechanical properties of the in situ silica composite. The pseudo-network structure of in situ silica was low, which resulted in a low storage modulus. By filling in situ silica in NR, thermal properties of composite material were also improved. These unique characteristics of the in situ silica composite can be ascribed to the well dispersed in situ silica particles within the NR matrix.