Fundamental studies of granule consolidation .1. Effects of binder content and binder viscosity

Granule consolidation was studied experimentally using a 0.3 m diameter laboratory granulation drum with fine glass ballotini as the model powder and glycerol-water mixtures as model liquid binders. Granule consolidation during tumbling was found to be a complex process controlled by the balance between the different mechanisms that resist granule deformation: interparticle friction and viscous dissipation. The rate of consolidation decreased with decreasing particle size. As liquid content increased, interparticle friction effects decreased but viscous losses became more significant. Thus, the effects of binder viscosity and liquid content were highly interactive. Unless the balance between the two mechanisms is accurately known for a given system, the effect of changes to binder parameters on granulation behaviour cannot be predicted, even qualitatively. To overcome these difficulties a new methodology for relating formulation properties to granulation behaviour is suggested based on bulk powder properties measured by triaxial consolidation tests and the development of a new granulation criterion for deformable granules. A procedure for testing critically the proposed methodology is presented.