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

Abstract

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 (eϭϪ0.1) and recovery (eϭ0) were measured for the samples filled with carbon blacks (CB) having different primary particle sizes. The change in EЈ 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.

Chain Anisotropy Effect on Polymer Nonlinear Viscoelasticity

“…After large shearing at strain gϭ0.5 and 1.0, decrease in GЈ and increase in tand were observed, but complete recovery was observed both in GЈ and tand. They are consistent with the results for the cross-linked SBRs measured for revering double-step compression experiments 9) . The results mean clearly that dynamic modulus and loss tangent are functions of chain configuration as discussed preliminarily in the introduction.…”

“…However, effect of entanglement network rupture may be included. Similar results on GЈ were observed again in the coarsely cross-linked polymer where no loss of entanglement was expected 8,9) . These results were all taken during the stress decay processes.…”

“…Figure 7 shows comparison of storage modulus and loss tangent values measured in different directions, that is, along the extensional axis and along another axis perpendicular to the extensional direction. For a usual rubber cross-linked at no deformation, the residual extensional strain of 0.27 would correspond to compressive strain of 0.11 in the normal direction under the condition of incompressibility of rubber, suggesting increase in GЈ from the value taken at equilibrium state, if we refer the data reported previously on GЈ of compressed vulcanizate 9) . However, significant difference cannot be found between the two curves observed in parallel and perpendicular directions to the extensional axis.…”

“…We could expect more direct experimental evidence, if we could keep the high anisotropic chain configuration in polymeric materials. In the previous papers 8,9) , chemical cross-linking was introduced in no deformation. To keep the anisotropic chain configuration, it should be introduced in a deformed state.…”

Controlling the Performance of Filled Rubbers

“…Filler particles may agglomerate to form secondary aggregates, which threedimensionally connect to form a filler network [18][19][20] that increases the tensile strength and modulus. However, the filler network 21,22) is easily broken into small aggregates after deformation because the filler-filler interaction is too weak to maintain the network structure. The Peyne effect 23) and Mullins effect 24) are shown in Figures 6 and 7, respectively.…”