A Review of the Rheology of Filled Viscoelastic Systems

We are concerned here with the effect of added filler particles on the linear and non-linear rheological properties of viscoelastic systems. Whilst the addition of spherical or near-spherical filler particles will almost always increase the level of both the linear and the non-linear viscometric properties (so leading to increases in pressure drops, etc.), we usually find a decrease in the level of the elasticity (in its various measures combining the first normal stress difference and the shear stress), as manifested in such important practical features such as extrudate swell, melt fracture, size of entry vortices, stress relaxation, Weissenberg effect, etc. However, the addition of high-aspect-ratio, fibre-like fillers can increase the elasticity as well as the viscosity. Occasionally, the absorption of chemical species from the continuous phase onto the surface of the disperse phase particles can complicate matters due to depletion of the continuous phase.