Particle Shape Descriptors and Angle of Repose of a Bimodal Distribution Sample

Particle size and shape influence the production of solid dosage forms. This study aimed to use the three shape descriptors available in the literature to describe the shapes of six compounds, and evaluate whether angle of repose might predict the flowability of a powder sample the same as those made by compressibility index and Hausner ratio. Images of cephalexin monohydrate, niacin, nystatin, sodium chloride, rifampin, triclosan were taken by a Raman Microscopy. Since the existing particle shape system could not characterize all six compounds, a new system is proposed. The powders of Rifampin and hydralazine hydrochloride were found to possess bimodal distribution during the study. Compressibility index and Hausner ratio predicted rifampin as poorly flowable, and predicted hydralazine hydrochloride as fairly flowable. But when either powder was poured through a test funnel, a dome formed in the middle of the horizontal base instead of the expected cone-like pile. This led to the question as to how the angles of repose should be measured. Our suggestion is that the angle of repose of a bimodal particle distribution powder be considered from the dome base in addition to the traditional approach, from the horizontal base, to avoid false prediction of flowability.