Characterization of the effect of the filler dispersion on the stress relaxation behavior of carbon black filled rubber composites

In the present work a new evaluation method for the characterization of the stress relaxation behavior of rubber–carbon black (CB) composites is presented. Using the chart of the online measured electrical conductance received from the recording equipment in the mixing chamber different rubber–CB composites with well defined state of the CB network have been produced for the stress relaxation investigation. The development of CB dispersion degree and the rubber-layer bonded on the CB surface have been characterized systematically using the method of the online measured electrical conductance and the thermogravimetric analysis of rubber–filler gel. The analysis of the stress relaxation curves is based on the division of the initial stress into several stress components and the consideration of the structure of the composites as a combination of different networks. The contribution of the stress component to the corresponding network is the focus of the present work. Based on the systematic variation of material parameters and test conditions we could divide the applied stress into six stress components which are originated from the rubber matrix and CB. It is obvious that the debonding of the rubber-layer from the CB surface and the collapse of a part of the CB network can be described by the relaxing stress component ΔσCB(rubber-layer) and ΔσCB(network), respectively. The non-relaxing stress components σ∞CB(rubber-layer) and σ∞CB(network) are dependent on the amount of the time-stable bonding in the rubber-layer and the stable part of the CB network. The mechanical performance of the composites and especially the time and temperature dependent mechanical behavior could be specifically modified by CB addition.