Wet granulation in high shear mixer : effect of physico-chemical properties on the growth kinetics

Abstract

The wet granulation process is sensitive to changes in product properties and process variables. The optimal process and formulation are based on the knowledge of the granule growth mechanisms and of the product properties and process variables effects. This paper presents some results obtained by the study of wet granulation of microcrystalline cellulose powder, MCC (Avicel PH101) using high-shear mixer granulators. It aims at understanding the effect of physicochemical properties, such as the viscosity and the wettability of a binder solution on solid particles surfaces, on the agglomeration kinetics. The experiments are carried out with various liquids having different surface tensions, viscosities, binder concentrations, etc. (water, aqueous solutions of sodium carboxymethylcellulose, polyvinylpyrrolidone, hydroxypropylméthylcellulose or non ionic surfactant oxo-C10C6 at a critical mycell concentration). The effect of the physicochemical properties is evaluated using a modified capillary viscous number, Ca’, which is defined, in this study, by the ratio between the viscous forces (LU) and the work of adhesion Wa=L(1+cos). The results show that for Ca’ <1, the viscosity of the solution does not significantly affect the granulation process. The dominant forces in the granulation process are the interfacial forces since increasing the work of adhesion enhances the growth kinetics. When Ca’ becomes higher than 1.64, the viscous forces predominate and control the granule growth