Chemistry in Carbon Black Dispersion

Abstract

Abstract The properties of carbon black and their effect on the physical properties of rubber vulcanizates have been extensively reported. The importance of particle size, reticulate structure, and surface characteristics are generally accepted. The beneficial effects of carbon black are believed to be due in large part to strong adsorption of rubber molecules on the carbon black surface. Many investigators have described the physical nature of this adsorption and have related it to the surface properties of the carbon black. Chemical bonding has also been suggested as being an important factor in the surface interaction between carbon black and rubber. The contribution of chemical bonding to the dispersion of carbon black and its effect on the physical properties of vulcanizates is the subject of the present paper. Gerke, Ganzhorn, Howland, and Smallwood and Bradley found almost twenty years ago that, when rubber-carbon black mixtures were heated at temperatures of 275–400° F, vulcanizates prepared from the mixtures had lower electrical conductivity, lower hysteresis, lower durometer hardness, higher modulus at large deformations, and greater resistance to abrasion than did vulcanizates of the corresponding unheated mixtures. These changes were ascribed to changes in the dispersion of the carbon black. Experimental data will be presented in this paper which suggest that these changes in carbon black dispersion are the result of chemical reactions between carbon black and rubber.