Cohesion of lactose powders at low consolidation stresses

The flow characteristics of a powder system are known to be influenced by particle size distribution, particularly the content of fine particles, and interparticle forces. This paper reports an investigation that has identified and quantified links between physical properties, viz size distribution, bulk density and particle density, and cohesion in compacted beds of powder. An annular shear cell was used in the determination of the cohesion of cohesive and free-flowing milled lactose powders at low consolidation stresses in the range 0.31–4.85 kPa and under ambient conditions. Following consideration of the compaction and shearing processes, it was postulated and confirmed that cohesion could be expressed as a function of powder surface area per unit volume and dimensionless preconsolidation stress. It was shown that care is needed in the measurement of surface–volume mean diameter when applying correlations developed from the experimental data.