(641a) Shear-Induced Compaction of Pharmaceutical Formulations

Properties such as density and flowability of pharmaceutical blends are often determined by the processing history. Moreover, blend properties can evolve in a divergent manner in different processing units. For example, the powder bed inside a rotating drum visibly dilates (expand in volume) up to 25%, depending on the powder composition, particle size and the rotation speed of the drum. On the other hand, the density of a lubricated powder processed in an annular cell shear can increase by 15-20%. The increase in cohesion plays a dominant role in flow dynamics, as it directly impacts the bulk flowability of solid material. In order to better understand the role of flow variables on the evolution of density under compressive shear conditions, experiments were performed in parallel with numerical DEM simulations in an annular cell using two configurations, one that includes equally spaced pins to promote uniformity of shear rate, and another, simpler configuration lacking the pins. DEM results show excellent qualitative agreement with experiments. Density after processing is higher that the initial ?bulk density?. The hypothesis is that the forces perpendicular to the direction of flow cause an inelastic compaction of the powder bed. Those forces are incremented using pins that restrict the area for the powder flow. The DEM results for the set-up with pins show a further increase in compaction forces.