2.4. Evaluation of Physical Properties of Powderized Solid Dispersions

Bulk density was determined by pouring pre-weighed and pre-sieved dispersion formulations into a graduated cylinder via a large funnel, and the volume was measured and recorded as the bulk volume. The cylinder was tapped until the powder bed volume reached a minimum, and this volume was recorded as the tapped volume. The bulk density and tapped density were calculated from Equations (1) and (2), respectively.

Carr’s index is known as percent compressibility, indirectly related to the flow rate, cohesiveness, and particle size. Compressibility is the ability of a powder to decrease in volume under pressure. Carr’s compressibility index of the powder was obtained from density determinations. It is a simple, fast, and accurate method of predicting powder flow characteristics. Carr’s index for each formulation was calculated using Equation (3) [40,41].

Hausner ratio, the ratio of tapped density to bulk density, is related to interparticle friction and can be used to predict powder flow properties. The Hausner ratio for each formulation was calculated using Equation (4) [40,41].

The flowability of solid dispersions was evaluated by measuring the angle of repose and the flow rate through a funnel. For measurement of the angle of repose, a fixed funnel method was used. Specifically, a fixed funnel (Copley Scientific Ltd., Nottingham, UK) with an orifice inner diameter of 10 mm and specially designed to evaluate the flowability of powders or granules was used. The funnel was fixed above a flat horizontal surface at an appropriate height. The orifice of the funnel was closed, and 10 g of solid dispersion was poured into the funnel. Then, the orifice of the funnel was opened, allowing the solid dispersion to pass through. The angle of repose (θ) of the conical piles formed by each formulation was calculated using Equation (5), after measuring the height (h) of each conical pile and the radius (r) of its base.