Comparative studies of powder flow predictions using milligrams of powder for identifying powder flow issues

Characterising powder flowability can be challenging when sample quantity is insufficient for a conventional shear cell test, especially in the pharmaceutical industry, where the cost of the active pharmaceutical ingredient (API) used is expensive at an early stage in the drug product development. A previous study demonstrated that powder flowability could be predicted based on powder physical properties and cohesiveness using a small quantity of powder samples (50 mg), but it remained an open question regarding the accuracy of the prediction compared to that measured using industry-standard shear cell testers and its potential to substitute the existing testers. In this study, 16 pharmaceutical powders were selected for a detailed comparative study of the predictive model. The flowability of the powders was predicted using a Bond number and given consolidation stresses, σ1, coupled with the model, where the Bond number represents powder cohesiveness. Compared to the measurements using a Powder Flow Tester (Brookfield) and an FT4 (Freeman Technology) Powder Rheometer shear cell tester, the results showed a good agreement between the predictions and the measurements (<22 % difference) from the two shear cell testers with different consolidation stresses, especially for cohesive materials. The model correctly predicts the class of flowability for 14 and 12 of the 16 powders for the PFT and the FT4, respectively. The study demonstrated that the prediction method of powder flowability using a small sample (50 mg) could substitute a standard shear cell test (>15 g) if the available amount of sample is small.