An investigation into the flowability of fine powders used in pharmaceutical industries

Abstract

This paper investigates into the flow properties of two popular pharmaceutical excipients (Calcium sulphate and Dicalcium phosphate) and their respective feeder hopper design requirements. There are numerous problems related to poor powder flowability that are faced by pharmaceutical industries, due to a lack of fundamental understanding of powder flow properties and their effects on hopper design parameters (Standard, 2008 [1]). Characterization tests confirmed that the Dicalcium phosphate powder displayed a smaller particle size, larger specific surface area and higher value of Hausner ratio compared to Calcium sulphate powder indicating that Dicalcium phosphate powders are markedly more cohesive. This was validated by the instantaneous and time consolidation flow function curves which showed that the Dicalcium phosphate was the more cohesive. Powder flow function and wall friction tests were carried out on a ring type shear tester working on the basis of Jenike's principle. Based on the instantaneous test results, Dicalcium phosphate was found to require a larger hopper outlet dimension for the same hopper half angle compared to Calcium sulphate. The time consolidation test results have shown that both Dicalcium phosphate and Calcium sulphate gained strength during static storage and have become more cohesive. A simple empirical model for powder cohesion and unconfined yield stress has been developed and validated with a number of experimental values derived from common pharmaceutical powders.