Rheological and Mechanical Properties of Styrene-Butadiene Rubber Compounds

The cure behavior, rheological property, and tensile strength of styrene-butadiene rubber (SBR) compounds containing different sizes of rubber powder vulcanizates (RPV) were investigated by varying the loading from 0 to 40 phr. Six different sizes of RPV were selected to see the effect of particle size. A typical reclaimed rubber powder was also used to see the reclaiming effect. The average particle size of the RPVs ranged from 70 to 2,000 μm. In the cure characteristics, as the powder loading was increased, the maximum torque, scorch time, and optimum cure time decreased, while minimum torque increased. At lower shear stresses (or shear strains) the viscosity of the rubber compounds increased noticeably with the addition of RPV. This increase was diminished at higher shear stresses. However, the die swell decreased when RPV was added. With increased powder loading the tensile strength decreased dramatically at lower powder concentrations, ∼ 10 phr, and then the rate of this decrease became slower at higher concentrations. A power-law relation was observed between the tensile strength reduction and the particle size of the RPV.