Effect of moisture and magnesium stearate concentration on flow properties of cohesive granular materials

In this article the gravitational displacement rheometer (GDR) is used to characterize the effects of formulation composition and environmental conditions (moisture) on flow properties of cohesive pharmaceutical powders under unconfined conditions. The amount of moisture in the sample often has important effects on the physical and chemical properties of pharmaceutical solids. Properties such as flow, compaction, disintegration, dissolution, hardness and chemical stability are all influenced by moisture. In the case of lactose, as moisture content increases in the powder bed, the flowability becomes poorer as the moisture condenses on the surface and increases cohesion. The celluloses show opposite effect as compared to lactose. Here, as moisture content increases, the flow properties improve dramatically. The GDR also captures the effect of lubricant concentration on the cohesion of powders. The presence of lubricant does not play any significant impact for free flowing powders, but as powder cohesion increases, the lubricants allow for improved flowability of powders. The GDR was also used for a case study of real drug formulation. The methodology was able to evaluate the impact of humidity and lubricant concentration on the flow properties of the formulation.