Sol-gel process of alkyltriethoxysilane in latex for alkylated silica formation in natural rubber

Sol-gel process of alkyltriethoxysilanes that was dispersed in natural rubber latex was used to generate alkylated silica particles inside the rubber matrix. Three types of alkyltriethoxysilanes were chosen, i.e., vinyltriethoxysilane (VTOS), ethyltriethoxysilane (ETOS), and i-butyltriethoxysilane (BTOS), as they differed in the type of one substituent group. Together with tetraethoxysilane (TEOS), a typical precursor for silica formation, all silanes were studied for their conversion to silica and subsequent reinforcement capabilities in sulfur-vulcanized rubber. The in situ generated silicas were fine and well dispersed in the rubber matrix, as analyzed by SEM and TEM. Solid-state 29Si-NMR technique was used to confirm the presence of alkyl substituents on the silica particles buried inside the rubber matrix. Tensile and tear properties of the in situ silica-filled NR vulcanizates were higher than those of the vulcanizate prepared by conventional mixed method. Among the three alkyltriethoxysilanes used, only VTOS, when used as a mixture with TEOS, did not cause a reduction in silica formation. The resulting vinylated silica tended to enhance the tensile modulus and resistant to tear of the rubber vulcanizates. Cure characteristic and swelling behavior in toluene of the silica-containing vulcanizates were also investigated. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers