Wet granulation in laboratory scale high shear mixers: Effect of binder properties

Abstract The effect of binder properties on torque curves, granule growth kinetics, wet mass consistency and dry granule strength has been investigated in this study. Granulation runs have been performed on a fine cohesive microcrystalline cellulose powder (Avicel 105, d 50  = 20 μm) in two types of laboratory high shear mixers: a Mi-Pro high shear mixer using a 1.9 L bowl and a 6 L Diosna high shear mixer. Binders used included ultra-pure water and solutions of varying concentrations of PVP and HPMC allowing us to cover different values for parameters like viscosity and work of adhesion. Torque curves recorded during granulation are found to allow good control of the process. Optimum liquid requirement for granulation has been found to vary with binder type and decrease with increasing viscosity while granule growth kinetics has been found to be to be related to the work of adhesion for low viscosity binders. Granule strength has been evaluated for wet granules by the means of wet mass consistency measurements on a mixer torque rheometer and for dried granules by means of uniaxial compression tests on a Texture Analyser mechanical testing machine. For low viscosity binders both wet mass consistency and dry granule strength have been found to depend on the work of adhesion. For high viscosity binders higher wet mass consistencies but lower dry granule strengths have been observed. Granulating on the larger 6 L scale has shown that constant impeller tip speed offers good agreement in terms of mean granule size however granule size distribution seems to be scale dependant.