1 Pharmaceutical Technology and Engineering, Department of Pharmacy, Faculty of Health and Medical Sciences, Københavns Universitet2 Department of Pharmacy, Faculty of Pharmaceutical Sciences, Københavns Universitet3 Department of Pharmacy, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark.4 Drug Research Academy A, Drug Research Academy, Faculty of Pharmaceutical Sciences, Københavns Universitet5 Danish Fundamental Metrology, Matematiktorvet 307, DK-2800 Kgs. Lyngby, Denmark.6 Department of Pharmacy, Faculty of Pharmaceutical Sciences, Københavns Universitet7 Drug Research Academy A, Drug Research Academy, Faculty of Pharmaceutical Sciences, Københavns Universitet8 Pharmaceutical Technology and Engineering, Department of Pharmacy, Faculty of Health and Medical Sciences, Københavns Universitet
Powder flow in small-scale equipment is challenging to predict. To meet this need, the impact of consolidation during powder flow characterization, the level of consolidation existing during discharge of powders from a tablet press hopper and the uncertainty of shear and wall friction measurements at small consolidation stresses were investigated. For this purpose, three grades of microcrystalline cellulose were used. Results showed that powder flow properties depend strongly on the consolidation during testing. The consolidation during discharge in terms of the major principal stress and wall normal stress were approximately 200Pa and 114Pa, respectively, in the critical transition from the converging to the lower vertical section of the hopper. The lower limit of consolidation for the shear and wall friction test was approximately 500Pa and 200Pa, respectively. At this consolidation level, the wall and shear stress resolution influences the precision of the measured powder flow properties. This study highlights the need for an improved experimental setup which would be capable of measuring the flow properties of powders under very small consolidation stresses with a high shear stress resolution. This will allow the accuracy, precision and applicability of the shear test to be improved for pharmaceutical applications.
International Journal of Pharmaceutics, 2014, Vol 475, Issue 1-2, p. 315-323