Mechanical Processing of Carbon Blacks. Resultant Effects in GR-S Compounds

Abstract

It was suggested that carbon blacks owe some of their characteristic properties to a tendency for individual particles to cluster into chainlike groupings or secondary aggregates. Results of mechanical processing experiments show that application of mechanical work altered or destroyed secondary aggregates. This conclusion was made since resistance to compression had been permanently overcome. Analytical measurements confirmed the supposition that secondary aggregates had been altered or destroyed, since oil absorption and liquid retention values markedly decreased with mechanical work. Finally, properties of compounded GR-S stocks were seriously altered—namely, smoothness of milled stock, high modulus, and enhanced electrical conductivity. It is concluded that these properties were originally caused by the presence of secondary aggregates or structure units. Alternative interpretations of these data are possible—namely, it might be concluded that it was not possible to disperse the densified material to the same extent as the original carbon black. However, this hypothesis contends that a large particle size material is being dispersed. Therefore, a decrease in tensile strength should have been noted. There is also some meager evidence suggesting that the chemical nature or activity of the carbon black surface was altered, so that its contribution to modulus was limited. It is believed, however, that most of the evidence offered by the data presented here preponderantly supports the structure theory of high modulus blacks. The authors consider these results as preliminary in the study of the structure properties of carbon blacks. They appear to be of sufficient interest to be brought to the attention of those studying reinforcement. Data available at present do not permit an interpretation of the contribution of structure to properties of “smooth-out” modulus and electrical conductivity of compounded rubber stocks.