Rheological study of a talc-based paste for extrusion-granulation

The rheological behaviour of an industrial talc-based paste featuring a solids volume fraction of 0.49 in a viscous aqueous surfactant solution was studied using a form of capillary rheometry. Standard approaches for determining wall slip velocities yielded non-physical results, although the data could be correlated using the Jastrzebski wall slip condition. The material was also characterised using the Benbow–Bridgwater approach and showed variations with die land diameter which could not be correlated using simple corrections. The parameters obtained featured an accuracy of ±20%. Density measurements indicated that dilation and liquid-phase migration were important features of the flow, and that the stresses are chiefly borne by the liquid-phase. The flow behaviour is interpreted in terms of the component properties: the difficulty in rheological characterisation is attributed to shear-induced re-orientation of the talc platelets during flow.