Characterization of wet powder flowability by shear cell measurements and compaction curves

Wet powders can be classified into the pendular, the funicular, and the capillary states. The boundaries between the three states depend on particle and bulk properties. The flow properties in each of these states vary with the level of saturation as both the tensile strength and the interparticle friction are a function of the amount of liquid present in the pores. In the frame of this study, it was demonstrated that wet powders can be classified based on shear cell measurements. Compaction curves are an adequate measure of wet powder flovvability and its dependency on particle and bulk properties. They can be used to evaluate the risk of blocking in extrusion processes. The significance of the transition from the funicular into the capillary state is highlighted, in particular for its distinct role in improving the flowability and the extrudability. (C) 2011 Elsevier B.V. All rights reserved.