CARBON BLACK DISTRIBUTION IN RUBBER BLENDS: A DYNAMIC-MECHANICAL ANALYSIS

The influence of phase morphology and carbon black distribution on energy storage and dissipation during dynamic excitations of rubber blends is discussed. It is shown that differences in the local stiffness of the phases in the glass transition regime of unfilled blends lead to characteristic deviations of the local strain from the external strain amplitude. These deviations are governed by a critical phenomenon due to the formation of a phase network above a critical blend ratio. As a result, a strongly nonlinear dependence of the glass transition maxima of the loss modulus on the volume fraction of the phases is observed. By counting the elastically effective bonds of the phase network, the local strain amplitude is estimated by purely geometrical arguments. Based on a consideration of the phase network, the distribution of carbon biack in the different phases of filled blends is estimated 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 loss modulus with rising carbon black concentration is exploited that relates the enhanced energy dissipation of filled rubbers to the internal friction of the filler particles. Results on EPDM/BR/N550 blends indicate that carbon black is preferably located in the BR phase. A somewhat higher concentration of carbon black in the SBR phase is found in the case of NR/SBR(40% Siyrene)/N330 blends.