Increasing the silanisation efficiency of silica compounds: Upscaling

Silica as a filler has a low compatibility with the rubber matrix due to its hydrophilic surface. A good dispersion of the filler can only be achieved by using a coupling agent, which reacts with the filler surface under the formation of a hydrophobic shell around the filler particle. During this chemical equilibrium reaction ethanol is generated and therefore the reaction rate is reduced by high concentrations of alcohol in the compound. The equilibrium can be shifted towards the silanisation products by removal of ethanol. Different mixing conditions for optimal ethanol evaporation were tested in laboratory mixers and scaled up to production size. Influencing factors such as rotor geometry, fill factor, air injection, temperature settings and ram position were investigated. An increase of the efficiency of alcohol removal by various measures indeed results in a higher efficiency of the silanisation reaction.