Carbon black distribution in rubber blends: A dynamic-mechanical analysis

The influence of phase morphology and carbon black distribution on energy s torage and dissipation during dynamic excitations of rubber blends is discu ssed. It is shown that differences in the local stiffness of the phases in the glass transition regime of unfilled blends lead to characteristic devia tions of the local strain from the external strain amplitude. These deviati ons are governed by a critical phenomenon due to the formation of a phase n etwork above a critical blend ratio. As a result, a strongly nonlinear depe ndence of the glass transition maxima of the loss modulus on the volume fra ction of the phases is observed. By counting the elastically effective bond s of the phase network, the local strain amplitude is estimated by purely g eometrical arguments. Based on a consideration of the phase network, the di stribution of carbon black in the different phases of filled blends is esti mated from the height of the local maxima of the loss modulus in the glass transition regime. Thereby, a linear increase of the maximum value of the l oss modulus with rising carbon black concentration is exploited that relate s the enhanced energy dissipation of filled rubbers to the internal frictio n of the filler particles. Results on EPDM/BR/N550 blends indicate that car bon black is preferably located in the BR phase. A somewhat higher concentr ation of carbon black in the SBR phase is found in the case of NR/SBR(40% S tyrene)/N330 blends.