Dynamic Testing and Reinforcement of Rubber

Abstract

Abstract A series of experiments have been run to determine which mechanisms dominate carbon black reinforcement of rubber. A broad range of compounds using oil-extended and non-oil-extended rubbers and carbon blacks covering the spectrum of tread blacks have been tested. The results for measurements made in an all-SBR formulation are reported here. The primary experiment consisted of measurement of the dynamic modulus and hysteresis of the cured and uncured compounds over a broad range of frequencies, temperatures, and strains. Ternperatures ranged from −70°C to +90°C; frequencies varied from 0.01 to 10 Hz; double strain amplitudes varied from 0.5% to 35%. From a discussion of the literature and evaluation of the experimental results, two mechanisms have been found to control the primary effects of carbon black on rubber reinforcement, where reinforcement refers to a general enhancement of properties, such as modulus, as well as the tensile strength of the compound. Hydrodynamic interaction, which is the increase in properties caused by the modification of strain fields in the region of an aggregate, dominates the large-strain dynamic and tensile properties of the compound. The primary carbon black variable in this mechanism is the effective aggregate size, such as measured by tint, which controls the effective volume loading of the carbon black at a given weight loading of carbon black. At low strains, the modulus is even higher than that predicted from the hydrodynamic-interaction/effective-volume model. This additional reinforcement is caused by the entanglement network formed between the tightly absorbed bound rubber on the carbon black surface and the bulk rubber far removed from the surface. The main carbon black variables in this mechanism are surface area and surface chemistry. The strain dependence of modulus is caused by the breaking and reforming of effective crosslinks in the rubber forming a transition zone between the bound rubber and the bulk rubber. To a large extent, this mechanism is dominated by the rubber properties, such as molecular weight and molecular-weight distribution. However, the dynamics of the entanglement network may be modified by altering specific interactions between carbon black and rubber.