Linear-Nonlinear Dichotomy of the Rheological Response of Particle-Filled Polymers

Understanding the complex rheological behavior of rubber compounds is an ever-present need as the rubber industry is moving toward more complex systems, i.e. functionalized polymers, non-traditional nanoparticles, reactive mixing, and other new technologies.  One unique aspect of the rheology of filled elastomers is that the incorporation of particles introduces a hysteretic softening (Payne effect) at small dynamic strains.  This study demonstrates that this nonlinear viscoelastic behavior needs to be considered when attempting to correlate steady shear response (Mooney viscosity) to oscillatory shear measurements from test equipment such as the Rubber Process Analyzer (RPA).  While a wide array of unfilled gum elastomers show good correlation between Mooney viscosity and dynamic torque from the RPA at all of the strain amplitudes used, rubber compounds containing silica and carbon black particles only exhibit good agreement between the two measures of processability when the oscillatory strain amplitude is high enough to sufficiently break up the filler network.  Other features of the filler network and its influence on nonlinear rheology are considered in this investigation, including the influence of polymer / filler interactions on filler flocculation and the use of Fourier transform rheometry to illustrate the “linear-nonlinear dichotomy” of the Payne effect.