Cure and mechanical behavior of rubber compounds containing ground vulcanizates .2. Mooney viscosity

Mooney viscosities and thixotropic behavior have been determined for SBR melts containing carbon black and/or ground vulcanizate particles. A composition containing ambiently ground rubber has a higher viscosity than one with cryogenically ground rubber. This is attributed to occlusion of continuum rubber within the sponge-like, ambiently ground rubber; occlusion is not possible with the smooth, cryo-ground particles. Viscosity was independent of particle size. On an equal phr (weight) basis, the addition of N330 carbon black and cryo-ground rubber augment Mooney viscosity to a similar extent. While the Guth-Gold Equation is approximately applicable to black-filled melts, samples containing ground rubber are a much better fit by the simple Einstein Equation. Ground rubber addition has only a minor influence of thixotropy, in contrast to carbon black, which greatly increases thixotropy.