Quantification of Powder Cohesion Using an Experimental Approach
In the pharmaceutical industry, the importance of particle technology has been relatively neglected. Particle technology, which makes up the majority of pharmaceutical manufacturing, is in crucial need of upgrade. As pharmaceutical products become more complex, better manufacturing technology is required to ensure product uniformity and performance. Shear plays an important role in the processing of pharmaceutical blends, affecting the performance of mixtures as well as their scale-up requirements. However, in spite of its significant impact, shear has not been studied systematically. Better manufacturing technology requires better understanding and control of product properties and process attributes. The cohesive strength and friction coefficient of granular materials are examples of such properties, and can be analyzed by shear testers. Several shear testers have been developed to analyze the flow properties of granular materials. In this poster, we present two different methodologies to characterize flow properties of cohesive granular materials. First, the ?controlled shear? Rheometer is designed to examine the effects of shear rate and total shear on pharmaceutical powder blends. Common pharmaceutical excipients and their mixtures are used for this experiment. The data collected from the sheared powder blends generally showed an increase in cohesion with an increase of applied shear and thus and increase in ?bulk density?. The second methodology utilizes the Gravitational Displacement Rheometer (GDR) to analyze the effects of cohesion on flow properties of pharmaceutical powders. The GDR consists of a rotating cylinder mounted on top of a load cell. As the cylinder rotates, the powder blend continuously exhibits characteristic avalanches, which are measured by the load cell. The avalanching dynamics of powders is substantially different from those observed for free flowing powders, or wet cohesive glass beads. Dry Cohesive powders such as the ones we utilize in this work exhibit history dependent flow dynamics, significant dilation, aperiodic avalanches and variable avalanching size. We also investigated the effect of lubricants using the GDR. As the powder cohesion is increased, lubricants played a major role in affecting the flow properties of the powders. On the other hand, introducing liquid in the system in the form of moisture showed variable effects for different materials. In some instances, adding moisture to the system increased cohesion, whereas in other cases, it had the opposite effect.