Comparative evaluation of powder flow parameters with reference to particle size and shape

Powder flow is critical to the success of various pharmaceutical processes such as tableting and capsule filling. Despite a plethora of flow characterisation techniques and parameters available, powder flow still remains to be a not well understood subject. Inter-relationships between the various powder flow parameters in particular have not been well established. Furthermore, while it is known that particle size and shape are important determinants of powder flow, their relative impact on individual flow parameter is unclear. In this study, granules were evaluated for their flow properties using various characterisation methods. Through multivariate analysis, flow parameters were classified based on the underlying physical granule property. Angle of repose, Hausner ratio, shear cell parameters and avalanche flow were found to be affected primarily by powder cohesion, which was in turn determined by the smallest granule size fraction. On the other hand, powder compressibility and inter-particulate friction were the main factors underlying basic flow energy. Angle of internal friction was primarily affected by particle roundness and did not appear to describe powder bulk flow properties. This study showed that while the various flow characterisation techniques were different in terms of their applications, there were common physical attributes that governed the measurements.