Tensile strength of filled GR‐S vulcanizates

Abstract The tensile strengths of high and low temperature GR‐S rubber vulcanizates containing various fillers have been measured. The fillers used were HAF black, calcium carbonate, and a high styrene‐butadiene copolymer (Pliolite S‐6). Measurements were made as a function of filler concentration, temperature, and degree of crosslinking. These measurements are compared with the predictions of a molecular theory for tensile strength previously published. The following major conclusions are drawn. (1) The theory previously presented for the tensile strength of rubbers is correct in general concept. (2) The increase in strength of GR‐S with added filler is a result of the fact that the filler particles distribute more widely the additional load imposed when a chain breaks. (3) In order for the filler to be effective, the polymer chains must adhere well to its surface. (4) The decrease in effectiveness of fillers at high temperatures is a direct result of the poorer adhesion at higher temperatures.