Bulk Density of Lactose Powders Under Low Consolidation Stresses

In the food and pharmaceutical industries, the shear testing protocol developed by Jenike in 1964 has been commonly used to characterize powder flow. The protocol requires the measurement of the stress required to shear a powder bed under a series of normal consolidation stresses and the consolidated bulk density. In this work, we report the bulk density of thirteen milled lactose powders of different particle size distribution measured with an annular shear cell at preconsolidation stress below 5 kPa. The bulk density ρB data can be modelled with two empirical expressions, namely [(ρB–ρ0)/ρB]=[asbsσpre/(1+bsσpre)] and [(ρB–ρ0)/ρ0]=[ks,M1+ks,M2log(σpre)], where as, bs, ks,M1, and ks,M2 are fitting parameters that reflect powder consolidation characteristics and σpre is the preconsolidation stress. The second correlation is found to be a more convenient tool for the prediction of bulk density because both ks,M1 and ks,M2 relate directly to the reciprocal of particle surface-volume mean diameter. Keywordsbulk density; cohesion; compression; lactose; shear cell