Fourier-Transform Rheology of Complex, Heterogeneous Rubber Materials

Filled rubber materials have a complex and heterogeneous structure. This results in a rheological behavior that is nonlinear already at very low shear strain. Despite this fact, most rheological measurements of such systems are analyzed according to linear parameters like storage and loss modulus due to a lack of knowledge about the interpretation of nonlinear parameters.

One method of interpreting nonlinear rheological data is Fourier-Transform (FT) rheology, which has been successfully applied for many complex soft systems like gels, emulsions and foams.

In this work we use FT rheology to investigate carbon black filled SBR. It was found, that the most important parameter for characterizing such materials is the nonlinearity I_3/1. A large influence of the filler volume fraction on I_3/1 is seen in large amplitude oscillatory shear even at shear amplitudes below 1 (i.e. 100%) due to an increase of the total filler surface area. This increase is most pronounced at filler loadings above the percolation threshold, showing the importance of the filler-filler network for the nonlinear behavior.

Furthermore poly(styrene-block-isoprene-block-styrene) with a spherical morphology of the polystyrene is investigated. Both, triblockcopolymers synthesized in our lab and industrial samples were used. These thermoplastic elastomers are another class of rubber materials with a high industrial importance and are also a model system for the more complex carbon black filled systems when the measurement temperature is below the glass transition temperature of polystyrene.