(598a) Yield Loci of Lactose Powders At Low Consolidation Stresses: Measurement and Modeling

We have previously demonstrated a correlation for model lactose powders in which cohesion is related to surface-volume mean diameter, in situ bulk density at the preconsolidation stress, and the preconsolidation stress normalized with the minimum value used; mean diameters ranged from 30 microns to 223 microns, and the preconsolidation stresses spanned the range, 0.31 kPa to 4.85 kPa. This work is now extended using the observation that (for the lactose test powders) the yield loci are essentially linear, and their slope does not exhibit much dependence on powder size or preconsolidation stress; for bulk density we have found that the value under compaction is well related to loose-poured density, by a logarithmic model. It is thus possible to reconstruct (linear) yield loci using estimates of cohesion, mean particle diameter, bulk density and preconsolidation stress, using size distribution information and loose poured density. The utility of reconstructed yield loci has been assessed by comparing estimates of minimum hopper exit opening, with values determined from primary measurements; in both cases, the angle of wall friction was for 304 stainless steel with a 2B mill surface finish. Exit dimension estimates from primary yield loci and reconstructed yield loci were generally in good accord.