(233au) Powder Tester Comparison to Predict Discharge Rate from Hoppers and Filling Tablet Press Dies

To enhance the productivity in the manufacturing of solid dosage forms it is important to ensure that powders flow from hoppers and into tablet press dies at appropriate rates to enable high throughput and reduce variation to minimize product defects. This paper discusses the results of different flow testers to describe flowability of materials and how they relate to solid dosage form production.

The manufacturing of tablets requires fine powders to flow through a number of hoppers, feeders and finally into dies of a tablet press. The authors evaluated the flowability of fine powders with commonly used powder characterization testers in the pharmaceutical industry namely shear testers, compressibility cells, permeability cells, and funnel, orifice plate and avalanche testers.

For this study the authors selected 10 cellulose ether excipients which are investigated for flowability assessment. The flowablity measured by the different flow testers is compared with the limiting flow rate based on Johansonâ??s work [1]. It was found that the discharge rate or flowability is best described by the permeability and the bulk density. The flow function or the flow factor could not describe the discharge rate appropriately. The Carr index describes the compressibility of a powder but cannot predict the discharge rate. However, the Carr index can be used to evaluate flowability trends if the variation of Carr index measurement is considered.

The impact of flowability of a material on tableting was evaluated experimentally with a Piccola bilayer press. It was found that the standard deviation of tablet weight, compaction force and radial tensile strength can be described as a function of flowability. With increasing flowability, the variability in all three metrics was reduced. Thus, powder flowability can be applied to understand variation in the tableting process. Consequently in this study the flowablity of all cellulose ether excipients was measured and it was shown that Methocel^TM DC2 has the best balance between flow properties and the above mentioned tableting metrics.

[1] Johanson, J. R., â??Two-Phase Flow Effects in Solids Processing and Handling,â? Chemical Engineering, pp. 77â??86 (Jan. 1, 1979)