THE DISPERSION OF CARBON-BLACK IN RUBBER .1. RAPID METHOD FOR ASSESSING QUALITY OF DISPERSION

Carbon black is the most important reinforcing filler for rubbers. The incorporation of carbon black into rubber vulcanizates generally gives improved strength, extensibility, fatigue resistance, abrasion resistance, etc. In order to exert its beneficial influence on the properties of rubber vulcanizates, the carbon black must be sufficiently dispersed therein. Indeed, poor dispersion can, in itself, give rise to detrimental effects (eg. reduced product life, poor performance in service, poor product appearance, poor processing characteristics, poor product uniformity, raw-material waste, high finished-product rejection rates, and excessive energy usage). These inadequacies are generally the result of the presence of rather large, undispersed agglomerates. The present work was initiated in order to develop an improved understanding of the carbon-black dispersion process including the understanding of factors which affect the kinetics of dispersion. The work described here is focused on methodology for reproducibly mixing carbon black with rubber in the laboratory, and reproducibility, but rapidly and easily estimating the degree of dispersion of the carbon black into the rubber as a function of mixing time. Procedures were developed for introducing rubber, filler, and other ingredients into a small, laboratory internal mixer and for mixing the batches for various periods of time. Also, an improved, simple-to-use, reproducible method for determining the degree of carbon black dispersion in rubber has been adapted. The extent of dispersion was correlated with various measures of tensile strength and with other performance-related properties.