Hydrated silicas modified by nonsilane pro-adhesion compounds

The surface modification of hydrated silicas, precipitated from a solution of sodium metasilicate and gaseous carbon dioxide, was carried out. The modification was conducted in three ways (modification with evaporation of the solvent, heating of the silica-modifying compound solution system in a reflux condenser, and surface modification in a vacuum evaporator), using various amounts of pro-adhesion compounds, dissolved in organic solvents or in water. The extent of modification was established on the basis of heats of immersion of silica in water and benzene, by estimating a loss of silica surface silanol groups in reaction with functional groups of pro-adhesion compounds, and by testing the agglomerability of primary silica particles by electron microscopy. The modified silicas were used as fillers in rubber mixtures based on SBR rubber. The effects of modifying agents were studied by measuring the physicomechanical properties of vulcanizates filled with the modified silicas. Silica surface modification with oxyethylene compounds leads to an evident hydrophobization of the surface. Following modification with oxyethylene compounds [in particular, following modification with 5(1-piperidyl)-3-oxapentanol and 4-aza-3-oxaoctanol], silicas exhibit a clearly elevated condensation of surface silanol groups. When applied for silica surface modification, amine derivatives of oxyethylene compounds clearly improved the tensile strength and modulus of the filled SBR vulcanizates.