Test methodA study of wall slip in the capillary flow of a filled rubber compound

The rheological properties of a filler-reinforced rubber compound were investigated by a dynamic shear rheometer and a rate-controlled capillary rheometer with two different shear modes: oscillatory shear and steady shear. Based on the experiments, we found a deviation between the complex viscosities and the steady shear viscosities, indicating an apparent failure of the Cox-Merz rule, due to the presence of wall slip in the capillary flow. A finite element simulation was utilized to analyze the wall slip in the capillary tests. Numerical results revealed that the capillary rheometer tended to underestimate the shear viscosity in the presence of wall slip, and an explanation to the experimental finding was proposed.