Analysis of Resistivity in a Rubber Compound

Abstract In the tire industry, good dispersion of carbon black in the rubber matrix is very important to obtain optimum mechanical properties of the compound. Usually, this dispersion can be classified in macrodispersion (for particles bigger than 10 μm) and microdispersion (for those smaller than 10 μm). It is known that good microdispersion enables better fatigue resistance and wear. If it is desired to control the degree of dispersion of uncured compounds during the different processes in the factory, it would be necessary to have a simple and rapid test to do it. An appropriate method to detect different degrees of dispersion is based on the measurement of the electrical resistivity of the rubber compound with dc or ac. In recent years, different factors that affect the resistivity of the compounds were studied in several research programs. The internal factors include structure, size, and dispersion of carbon-black particles, the presence of other reinforcement (silica), and the polymer class. Other factors studied are external: mixing level, pressure, temperature, aging, and contact resistance. Boonstra showed that resistivity depends on the degree of dispersion of carbon black. In his paper, resistivity data are compared with the dispersion levels according to the Cabot rating with good correlation. Furthermore, there are several electrical conduction mechanisms that are proposed in the literature to explain experimental data. It is the purpose of this paper to present an improvement of the Boonstra device for the measurement of electrical resistivity of uncured compounds. The influence of temperature, pressure, aging, carbon black level, and time on the mill roll over the electrical resistivity were also studied. Finally, the results were analyzed by a probability model.