The effect of apparent density of sulfidic crosslink and their chemical nature on self-heat build-up in carbon black filled Natural Rubber under cyclic mechanical loading

Abstract

Natural rubber is a widely used elastomer for the preparation of cyclically mechanically loaded products such as tires, where it reduces self-heating behavior. From a material point of view, the degree of self-heating depends on the composition of the rubber compound. One of the parameters influencing the self-heating of rubber is the type of curing system, which leads to different crosslinking density. The crosslinking density value for carbon black filled rubbers is only apparent due to the its physical interactions present and is referred to as the apparent crosslinking density (aCLD).Therefore, this work focuses on investigating the effect of sulfur intermolecular network formation by conventional (CV), semi-efficient (SEV) and efficient (EV) curing systems on the temperature development of cyclically loaded rubber using an advanced test method to in-situ determine the heat build-up. Rubber samples based on different curing systems were prepared by varying the concentration of the accelerator N-Tertiarybutyl-2-benzothiazole sulfenamide (TBBS) at a constant concentration of sulfur (2.5 phr). Using basic mechanical tests, it was found that the stiffness and hardness of the rubber increased with increasing aCLD and decreasing proportion of poly-sulfide bonds, respectively. Furthermore, cyclic mechanical analysis showed that with increasing aCLD and parallel decrease in the proportion of poly-sulfide bonds, both the loss modulus (G'') and dissipated strain energy increased, which was also reflected in the values of the mechanical stress-induced self-heating gradient. From the values of maximum developed temperatures, it was evident that the group of material with CV curing system showed the lowest self-heat build-up.