The nonlinear rheology of styrene-butadiene rubber filled with carbon-black or silica particles is investigated by complementary viscosimetric devices on a wide range of deformation and deformation rates. The effect of filler volume fraction on the rheological behaviour is systematically studied. The importance of a critical volume fraction (percolation threshold) is outlined, giving rise to a network structure at rest. At finite deformation, this structure is destroyed and the compounds exhibit a non-linear rheology quite similar to the unfilled rubber. The separability of time and strain effects on the relaxation modulus is observed not only for the pure elastomer, but also for the filled compounds. Several viscoelastic functions of the filled compounds (linear viscoelastic moduli, damping function, and shear-stress) can be rescaled using a concentration shift factor that is identical to the one used in Newtonian suspension rheology

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Uncured compounds of SBR1500 with various levels of silica were studied using a torsional dynamic tester (rubber process analyzer; RPA). Silica-filled compounds were prepared with the appropriate amounts (8.2%) of silane, i.e., bis(3-triethoxysilylpropyl)tetrasulfane (TESPT). A carbon black-filled compound was also studied for comparison. Strain sweep tests at constant frequency show that filled rubber materials exhibit either no or limited linear viscoelastic domain. Frequency sweep tests were performed either at the lowest strain amplitude or within the linear range at several temperatures; results were treated through time-temperature superposition in order to yield GЈ and GЉ master curves at the reference temperature of 100°C. Special test procedures were applied that are known to give interesting information about the morphology of complex polymer systems: the morphology damaging test (MDT) and the damaged morphology recovery test (DMRT). Results obtained are discussed with respect to the likely morphology of carbon black and silica-filled rubber compounds.

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ABSTRACT:The viscoelastic properties of filled elastomers (uncured styrene-butadiene rubber filled with carbon black) were investigated with two shear rheometers specially designed for the characterization of complex polymer systems. A torsional strain-controlled rheometer [i.e., a rubber process analyzer (RPA)] was used in dynamic and relaxation modes for measuring the storage and loss moduli and the relaxation modulus. A stress-controlled sliding cylinder rheometer (SCR) was operated for the measurement of the creep compliance. Both devices could be operated on a large scale of imposed strains or stresses ranging from the linear viscoelastic regime to the nonlinear viscoelastic regime, and they were complementary in supporting the original viscoelastic behavior of filled elastomers for a wide experimental time range. Moreover, when the measuring ranges of the two apparatus overlapped, a cross-check of the material functions obtained with the RPA or SCR could be successfully carried out. This validation of the data was performed not only in the linear domain of viscoelasticity, with the classical approach of a generalized Maxwell model, but also in the nonlinear domain, with a viscoelastic integral model of type K-BKZ.