Granulation behaviour of increasingly hydrophobic mixtures

Wet granulation is the formation of powder particle assemblies bound by a liquid binder. Granules are produced in order to prevent mixture segregation, improve flow characteristics and ease of powder handling. The liquid binder droplets penetrate into, and bind together, powder particles being agitated in a mixer. Real granulation formulations are complex and challenging. The difficulty of achieving controlled water based wet granulation of a formulation containing a hydrophobic component is one such challenge that is receiving increasing attention in academic and industrial research. esent work has focussed on the granulation of multicomponent batches, specifically mixtures of hydrophilic Granulac230 (lactose) and hydrophobic limestone, using different spray droplet sizes and impeller speeds. The granulation behaviour of the batches is assessed in terms of granule size and compositional distributions on increasing the hydrophobic content of the batch. Transitions in granulation behaviour are reported as the hydrophobic content of the batch is increased. The granulation behaviour is linked to static powder bed penetration times by assigning ‘compositional zones’, which could be used as a predictive tool in formulation and process development In addition, a new preferential nucleation and layering mechanism is proposed to describe the experimental data and better understand how the ‘compositional zones’ of granulation behaviour have arisen.