Executive Summary
The primary project aims are to develop relationships which predict the wet massing behaviour of particulate solids granulated with binders by mechanical agitation, and to apply such findings in probing scale-up factors.
Work with model substrates:polymer binder systems has previously shown the critical estimate from surface free energy measurements, in determining the wet-massing and rheological character of the role of solid:liquid interfacial phenomena, particulate systems during granulation. This approach has been employed to predict the wet-massing behaviour of four representative powder substrates - two microcrystalline celluloses, calcium carbonate and griseofulvin - granulated with two aqueous polymer binders - polyvinylpyrrolidone and hydroxypropylmethylcellulose. The findings have been tested with a new mixer torque rheometer, which has been shown to provide data which can be directly related to the theological terms yield stress (T), kinematic viscosity (7) and degree of non-Newtonian rheological behaviour (n).
In general, the rheological behaviour of the various substrate:binder systems was consistent with the predictions made from surface free energy calculations, and followed similar patterns to those observed for model substrates. The spreading of substrate and binder components were critical factors in influencing the stability of the wet masses in the domains where, in industrial processes, many granules are prepared. Preliminary observations with mixed powder substrates suggest that topographical features of particulates also play an important role in determining rheological behaviour during granulation.
In the scale-up studies, a modified power number/Reynolds number relationship has been developed and successfully applied to large scale (up to 600L) mixer granulators. This approach has shown that, via measurements of wet mass rheology by mixer torque rheometry, a master surve for a specific formulation can be prepared using laboratory scale equipment which allows prediction of optimal granulation end-point conditions for large scale production equipment.