Influences of Flowability and Permeability on Air Elutriation Segregation of Pharmaceutical Powders
Segregation in bulk solids is an undesirable phenomenon, in which particle size distribution varies at different location in a storage vessel causing significant changes in handling processes due to a number of mechanisms. One influence factor is airflow when the powders are handled in loading and offloading processes. Due to air flow, fine particles move differently from coarser ones, causing changes of particle distributions within the batch. This size change can be critical to industries including pharmaceuticals and food, compromising quality of final products and leading to failures in quality control. In order to control segregation, it is important to understand segregation mechanisms and the influence factors such as material physical properties.
In this study, air induced segregation of pharmaceutical powders has been studied by using an ASTM elutriation tester. 3 size grades of Lactose and one grade of Mannitol have been used for segregation study. These materials have flow functions ranging from free flowing to slightly cohesive. Also, permeabilities of the materials have been measured and fluidisation air velocities have been determined. The results show interesting linkages between material segregation behaviours and these material physical properties. The reasons for the linkage are thought to be due to the principle that segregation of powders may be controlled by adhesion forces and number of contacts between particles, so adjusting or selecting these carefully could be a useful technique in control of material segregation.