Carbon Black Morphology in Rubber

Abstract

Abstract Electron microscope image analysis of carbon blacks in specific rubber compounds has greatly expanded the range of useful applications for studies of this type. This dispersed carbon-gel procedure has improved the sampling and test precision at operating speeds that are now reasonably comparable to the simple colloidal procedures for characterizing carbon black. Improved models have been developed for deriving black surface area and intraunit occlusion capacity. The EM image analysis approach has been useful in applying certain principles of reinforcement theory, as well as in explaining rubber property differences that are attributable to carbon black variables. Studies on hysteresis at constant strain (E″) have indicated that the important black variables, in diminishing order of significance, are loading, structure (intraunit occlusion and anisometry), unit size, unit size distribution, and surface activity. For hysteresis at constant energy (resilience), the most important black variables appear to be black loading, unit size, unit size distribution, surface activity, and structure. In terms of tread wear resistance (moderate wear rates with SBR-BR), a somewhat different pattern of carbon black variables is apparent. At constant loading, the most important black properties appear to be specific surface area, surface activity, structure, and unit size distribution. At any given tread wear-surface area level, hysteresis can be lowered by broadening the unit size distribution and increasing the surface activity of the black.