Modeling and practice of ethanol devolatilization from silica–silane rubber compounds in an internal mixer
WILMA DIERKES* and JACQUES W. M. NOORDERMEER Twente University, Faculty of Engineering Technology, Department of Elastomer Technology and Engineering, P.O. Box 217, 7500 AE Enschede, The Netherlands
Abstract-During mixing of a rubber compound containing silica and silane, the mixer is not only used for the dispersion of the filler and other ingredients, but also for a chemical reaction. These two functions of the mixer result in opposite processing requirements. A good dispersion is attained by high shearing forces, increasing the compound temperature. The silanization does not depend on shearing forces; it is positively influenced by high temperatures, but with an increasing risk of prescorch. Another drawback is the fact that the equilibrium between the ethanol concentration in the vapor phase in the void space of the mixing chamber and the ethanol concentration in the rubber phase limits the reaction rate of silanization. Devolatilization of the compound is a crucial factor for an efficient silanization reaction. A model for ethanol devolatilization from a rubber compound in an internal mixer is developed, including a chemical reaction replenishing the volatile component during the devolatilization process. The model is based on the penetration theory, with the main contribution to devolatilization being the mass transfer. It is compared with experimental data, resulting in the conclusion that the situation in the internal mixer can best be described by mass transport between the surface layer of the rubber phase and the vapor phase.