Reinforcement of natural rubber by silica generated from sol-gel process of silanes in latex

Abstract

Alkyltriethoxysilanes and tetraethoxysilane (TEOS) were used as precursors to generate silica in concentrated natural rubber latex. Both silanes were mixed with the concentrated latex incorporated 0.7% NH3, and heated at 50°C for 5 days in order to complete the sol-gel process of both silanes. Four types of ethoxysilanes ; tetraethoxysilane (TEOS), vinyltriethoxysilane (VTOS), ethyltriethoxysilane (ETOS), and i-butyltriethoxysilane (BTOS), were studied. The conversion of silane to silica particles inside the rubber depended on size and polarity of the alkyl group in the alkyltriethoxysilane. The influences of various molar ratios between alkyl-triethoxysilane and TEOS on the morphology and mechanical properties of the composites were investigated. The modified silica particles obtained from the mixed silanes were well dispersed in the NR matrix as observed by SEM and TEM. Silicon-29 solid-state NMR technique was also used to analyze the chemical structures of the in siru generated silica. For sulfur-cured composites, the use of VTOS/TEOS (5, l0 and 20 mol% VTOS) resulted in an increase of tensile modulus, tensile strength, and tear strength over to the composite prepared from only TEOS. The mechanical properties results lead to a conclusion that the vinyl group from VTOS most probably participates in the sulfur vulcanization. Cure characteristic and swelling behavior in toluene were also investigated.