Characterization of New Technology Carbon Blacks

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Abstract
In this paper we have examined a limited number of conventional and new technology blacks, using the “t” method of nitrogen adsorption for comparison of surface area and dibutyl phthalate adsorption (DBPA) for comparison of structure. At a given “t” area the new technology blacks are of lower iodine number; conversely, at a given iodine number, the new technology blacks are of higher “t” area. This is not due to porosity, but rather to differences in carbon black-iodine surface interaction. The DBPA tests gives a fairly consistent measure of carbon black structure in rubber, for both types of blacks. An important difference between the two classes of black is in the higher tinting strength of new technology blacks, at a given “solid sphere” diameter (which depends primarily on the “t” area and to a lesser extent on the DBPA). We have introduced the use of a disk photosedimentometer for studying carbon black aggregate size distributions and have found that at a given “t” area, the distribution curves for the new technology blacks are shifted in the direction of smaller Stokes diameters. This can account, at least qualitatively, for their higher tinting strength. Electron microscopy supports the shift in Stokes diameters, at least qualitatively, and also indicates a more open aggregate morphology for the new technology blacks. The new technology blacks impart a higher level of reinforcement, at the same “t” area, as shown by tensile strength and roadwear. This is accompanied by a higher loss tangent or lower rebound. These properties may be due in part to a higher surface activity, as shown by a higher moisture adsorption and higher bound rubber, and partly to morphological differences, as shown by the smaller Stokes diameters and higher tinting strength. In summary, the higher bound rubber and higher tinting strength of the new technology blacks reflect differences in surface activity and aggregate size, which are responsible for the superior reinforcement shown by these blacks at a given “t” area.

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