287835 Relationships Between Particle Properties of Fine Powders and Flow Properties Under Low Compaction Stresses
In the food and pharmaceutical industries, significant amounts of process material are in the form of fine powder. Fine powders in general do not flow well because of their cohesive nature, and various characterization methods have been used to predict powder flowability. We present here results for thirteen model lactose powders, in which Hausner ratio and powder flow function data, i.e. compaction stress/powder strength data, have been correlated with size descriptors, as well as with each other. Particle size distribution was measured by the laser diffraction method (Mastersizer 2000, Malvern Instruments Ltd, UK); the key size descriptors used were surface-volume diameter, d32, and span, (d90–d10)/d50. Hausner ratio, ρtap/ρB, was determined with tapped density, ρtap, measured according to a GEA Niro standard for dairy powders at 1250 taps in accordance with the European Pharmacopoeia; loose bulk density, ρB, was based on New Zealand Standard 3111. An annular shear cell (Brookfield Engineering Laboratories, USA) operated at low compaction stresses, in the range 0.31–4.85 kPa, was used to obtain powder flow functions, and hence estimates of particle cohesion, C, and Jenike flow index, σc/σy; σc is the major consolidating stress and σy is the unconfined yield stress. Hausner ratio and C increased with decreasing d32 and increasing span, while σc/σy increased with increasing d32 and decreasing span. A plot of Hausner ratio versus σc/σy at 4–6 kPa suggested a power correlation, and the relationship between Hausner ratio and C appeared linear.
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