Modeling and practice of ethanol-devolatilization of silica-silane rubber compounds in an internal mixer

During mixing of a silica-silane rubber compound, the mixer is not only used for dispersion, but also for a chemical reaction. A good dispersion is reached by high shearing forces, preferably applied at lower temperatures, whereas the reaction rate of the silanization is increased with increasing temperature, but at the expense of scorch safety. Another limiting factor for the silanization reaction is the ethanol concentration, requiring effective devolatilization of the compound. A model for the devolatilization of a silica compound in an internal mixer is theoretically derived and experimentally verified. The most important factors are identified: the frequency of surface renewal and the surface-to-volume ratio of the compound as well as a low ethanol pressure in the void space of the mixer are the main contributors.