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. (C) 2003 Elsevier Ltd. All rights reserved.