Characterization of Powder Flowability for Die Filling

Inter-tablet variations in composition and weight depend on the flowability of pharmaceutical formulations. In this study, the concept of critical filling speed, which was proposed to characterize the flowability with special application to die filling, is evaluated and compared with other powder flow characterization techniques. It has been found that the critical filling speed provides a consistent gauge of the powder flowability with the poured angle of repose, Carr index, Hausner ratio, and flow functions from shear cell testing. However, the mass flow rate and the time to discharge a certain amount of powder through flowmeters showed a different trend, indicating that different powder flow behaviors are involved in these tests. This implies it is necessary to employ a powder flowability measurement technique that mimics the powder flow behavior in the actual application.