Dispersion mechanisms of carbon black in an elastomer matrix

Introduction The mixing of carbon black or silica pellets and a matrix implies distinct phases e.g., (i) incorporation, (ii) distribution and (iii) dispersion [Nak81]. To disperse implies to reduce the pellet size (around the millimeter) down to the aggregate size (a few tens of nanometers). This size is necessary to ensure the reinforcement of the matrix (see for example [Ham00]). Dispersion and distribution processes will define the dispersion state of the carbon black in the final product and thus its end-use properties. A prediction of the mixing process (after the incorporation step) including a local evolution of the size distribution of the carbon black pellets implies an exact modeling of the flow and temperature fields in the mixer and a good knowledge of the laws governing the dispersion mechanisms. Although the mixing of filler particles and a matrix is a common operation, the mechanisms responsible for the size reduction of the filler are not fully understood. One way to improve this knowledge would be to be able to observe inside the mixer what happens, which is not possible. Rheo-optical techniques recently appeared as a relevant tool to investigate in-situ dispersion but in a simpler flow (shear). However most studies concerned the dispersion of fillers in low viscosity matrices [RFM90-91, YMF97-98, SN01, PMF03].