Factors Influencing the Mechanical Behavior of Raw Unfilled Natural Rubber

Abstract

Abstract The influence of gel and soluble nonrubbers on the relaxation behavior of raw, bale NR has been studied by testing fractionated and solvent-extracted rubber. The fractionation was carried out by progressive dissolution, each fraction being recovered by evaporation of the solvent. The tests were performed in tension for extensions up to 70%. Removal of the soluble nonrubbers from the bale was found to decrease the rate of stress relaxation quite markedly, especially at longer times. The fractions fell broadly into three categories: sol rubber, “sol + microgel”, and undissolved macrogel. The last, in the case of the more complete dissolution, was an extremely stiff, almost nonrelaxing material. Despite this, the relaxation behavior of the whole bale rubber was closely reproduced by the “sol / microgel” fraction. Comparison of this fraction with the sol rubber showed that the microgel had predominantly a stiffening effect, though it did also significantly reduce the rate of relaxation.