RESISTIVITY AND SURFACE-ROUGHNESS ANALYSES FOR EVALUATING CARBON-BLACK DISPERSION IN RUBBER

Good dispersion of carbon black is essential in rubber compounding for obtaining optimum vulcanizate properties. The dispersion of a filler in a matrix can be defined as the distribution of the filler particle size and that of interparticle distance in the matrix. The uniformity of these distributions dictates the uniformity of the dispersion. This paper reviews various techniques used for measurements of carbon black dispersions and evaluates them in terms of their mobility in practice. The discussion covers the following subjects - optical methods; electrical methods; surface analysis; microscopy. A comparison of the three techniques shows that while all can discriminate dispersions, their useful ranges are different. The electrical resistivity method is relatively insensitive at the early stages of mixing but has a high sensitivity at the intermediate and latter stages. Each technique works quite well at intermediate dispersions and only loses sensitivity at very good dispersions. These methods differ from the resistivity in that they are sensitive to the undispersed filler. The surface analysis is a more objective and quantitative technique than the Phillips rating.