Dependence of Bound Rubber on Concentration of Filler and on Temperature. I
Abstract The change in quantity of rubber gel with the concentration of carbon black in filled natural rubber compounds was studied. It was established that there is a linear relationship between the amount of rubber gel and the black concentration, within a range of 20 to 80 parts of black to 100 parts by weight of rubber. No clear-cut relation exists between the quantities of rubber gel or the constants for the linear relations and the physicomechanical properties of the vulcanizates. The factors upon which the amount of bound rubber depend, i.e., the degree of degradation of the rubber, the heat treatment of the mixtures and the extraction temperature, do not alter the linear character of the cited relation. The critical concentration of certain types of blacks was determined. Up to this concentration no coherent rubber/black gel system is formed. The critical values for the black concentration are clearly related to some of the elastic properties of the filled vulcanizate.