Dispersive Mixing in Internal Mixers—A Theoretical Model Based on Agglomerate Rupture

Abstract

Abstract The mixing of solid additives into a matrix of rubber or plastics is an energy intensive process. Such a mixing operation generally involves rupture of agglomerates formed by the solid phase, separation of closely packed particles after rupture, and distribution of the separated particles throughout the polymeric matrix. Dispersive or intensive mixing refers primarily to the first two steps, whereas, the third step is by and large an extensive mixing process. Depending upon the polymer-additive system and mixer machine design, each of these steps may be rate determining. The most important and most investigated system is the carbon black-elastomer system. Mixing of such a system is generally carried out in batch Banbury type internal mixers (Figure 1). The dispersive mixing process in internal mixers is quite complex with many subtle features. A detailed review of the subject is outside the scope of this paper. However, careful reading of reviews and publications in the field, indicate that a great deal is known about the mixing process in internal mixers, the scale-up procedures using various criteria, the effect of the mixing process and mixer geometry on processability and ultimate properties, and the flow patterns and fluid dynamics in the various regions of mixers. However, there seems to be no published attempt to a priori predict the mixing process from fundamental considerations.