Novel precipitated silicas: an active filler of synthetic rubber

Highly dispersed silicas have been obtained at a semi-technical scale by precipitation from sodium metasilicate solutions using appropriately diluted solutions of ammonium hydrogencarbonate or ammonium chloride. The difference, as compared to the generally applied technology of silica precipitation using acids or their anhydrides, has been the involvement of the precipitation reaction in alkaline media. Attempts have been made at changing the silica surface character from hydrophilic to more hydrophobic, using a modifier from the group of silane coupling agents. The alkoxysilanes modifiers contained groups with chemical affinity towards functional groups of butadiene–styrene rubber. Modification of silica surface using silane coupling agents has been found to improve the reinforcement of vulcanizates, by increasing the tensile and tear strength in particular.