Hardness of moist agglomerates in relation to interparticle friction, granule liquid content and nature

Wet agglomerates deform plastically until they break through crack propagation. On the particulate level, liquid bridges are responsible for the strength of the wet agglomerate as they hold the particles together. The experiments reported in this paper identify the role of liquid surface tension, bridge Laplace pressure and liquid viscosity, which, in combination, explain the axial strength of pendular liquid bridges. Different situations exist depending on the degree the liquid wets the particles, and on the saturation of the agglomerate mass. A parabolic approximation can be used to describe the shapes adopted by pendular liquid bridges. On the wet agglomerate level, the hardness is related to three factors: the liquid binder surface tension and viscosity and the interparticle friction. A simple model is developed in this paper, based on the powder and liquid binder properties, which shows that the forces due to interparticle friction are generally predominant in wet agglomerates made from non-spherical particles. Although mechanical interlocking is not predicted, this model yields accurate prediction of wet agglomerate hardness independently measured on wet masses of varying composition. This theoretical hardness could prove an interesting tool for wet granulation research and technology. (C) 2001 Elsevier Science B.V. All rights reserved.