Interaction Between the Carbon Black Filler Particles
Interactions between the carbon black filler particles are due to the existence of primary particle aggregates and the agglomeration of these aggregates by physical bonds. In contrast to isolated carbon black primaries that are practically completely incompressible and show a negligible deformation, high-structure carbon black exhibits a large amount of elastic recovery. The carbon black network which exists in a rubber vulcanizate containing about 50 parts per hundred (phr) of high-structure carbon black is broken at rather small deformation (about 5% in unidirectional elongation) and loses most of its elasticity. However, the network reforms after sufficient rest time and is assumed to play a part in the hysteresis losses of the vulcanizate under cyclic larger deformation: the fragments of the network continue to be broken and reformed. Under severe attrition conditions, the stronger, covalently bound particle aggregates themselves may break. The electrical conductivity of the elastomer composite follows the same pattern as the elastic modulus. At low amplitude, when the carbon black network is still intact, conductivity is high, but it diminishes rapidly at higher amplitudes in conjunction with the elastic modulus as the carbon black network is broken.