Novel Characterization of Filler Network in Rubber Materials Using Differential Dynamic Modulus in Large Compression and Recovery

Rubber materials are made of two networks, chemical and filler networks. The networks are characterized usually by overall network density estimated at equilibrium condition. However, rubbers are used in nonlinear conditions where the filler network may change from the one at equilibrium. We need additional information on the filler network. Hence, differential dynamic modulus (DDM) in large compression (e=−0.1) and recovery (e=0) were measured for the samples filled with carbon blacks (CB) having different primary particle sizes. The change in E′ for unfilled sample was reversible in large compression followed by recovery, while those for filled samples were irreversible, showing change in filler network in large deformation. The differences in DDM at the recovered and the initial states were compared for characterization of the filler network. The difference for the sample filled with smaller CB was larger than the one with larger CB. The results show that the rubber filled with CB having smaller particle size makes weaker filler network. In addition, we observed the restoration behavior of the filler network structure. Recovery of filler network ruptured due to large compression and recovery in shape was attained at a time scale depending on particle size. The characteristic time was found to increase with increase in the CB particle size. It was concluded that the restoration process of CB filler network is based on diffusion of CB aggregate.