Granulation is a size enlargement process generally involving the agglomeration of particles often with liquid binders using specialised processing equipment. The dried granules in some cases, are further processed into compacts or tablets. Whilst widely used throughout industry the granulation process and related aspects, such as formulation design and scale-up procedures, are in general inadequately described.
With increasing industrial need for directed formulation design linked to prediction ,of processing performance and efficient scale-up of granulation, specific project objectives were defined, and several inter-related study areas identified with a view to providing much needed insight to address these issues. The research areas were the physico-chemical interactions between components to aid directed formulation design, the rheology of the wet- mass during granulation for process evaluation knowledge, and scale-up strategies for specific types of processing equipment. Within the project remit of granulation by mechanical agitation, high shear mixer-granulators were selected for the scale-up studies. This project has successfully researched several key aspects in these areas, generated valuable information and knowledge, and developed practically useful guidelines for industrial application.
From an extensive literature review, it was recognised, that the physicochemical interactions between granule components, whilst critically important during granulation, were poorly understood. Through a surface free energy (SFE) approach to derive a group of spreading and interaction coefficients, a model has been developed to predict the nature of material interactions which direct the structure and properties of granules. The model was tested with model systems using both physical evaluation and mixer torque rheometry, then successfully applied to a number of experimental particulate substances of diverse chemical composition granulated with two typical polymeric binders - HPMC and PVP. This procedure thus provides the basis of a rational approach to material selection in granule formulatin design.