Effect of particle shape on powder flowability of microcrystalline cellulose as determined using the vibration shear tube method.

Powder flowability of microcrystalline cellulose particles having different particle shapes, whose aspect ratios ranged from 1.8 to 6.4, was measured using the vibration shear tube method. Particles lubricated with magnesium stearate were also investigated in order to evaluate the effect of surface modification on powder flowability. Particles were discharged through a narrow gap between a vibrating tube edge and a flat bottom surface, where each particle experienced high shear forces, thus, overcoming adhesion and friction forces. Vibration amplitude was increased at a constant rate during measurement and the masses of the discharged particles were measured at consistent time intervals. Flowability profiles, i.e., the relationships between the mass flow rates of the discharged particles and their vibration accelerations, were obtained from these measurements. Critical vibration accelerations and characteristic mass flow rates were then determined from flowability profiles in order to evaluate static and dynamic friction properties. The results were compared with those obtained using conventional methods. It was found that angle of repose and compressibility were related to static and dynamic friction properties. Furthermore, it was found that particle aspect ratio more significantly affects powder flowability than does lubrication with magnesium stearate.