Influence of melting and rheological properties of fatty binders on the melt granulation process in a high-shear mixer

The preparation of granules by melt granulation was investigated using a laboratory-scale high-shear mixer (Pellmix PL 1/8) and binary mixtures containing lactose and different lipidic binders, namely, Compritol (R) 888, Cutina (R) HR, or Precirol (R) AT05. During the process, the product temperature and the impeller motor power consumption were monitored. On the other hand, the melting behavior (thermal analysis) and the rheological properties (controlled stress capillary rheometer) of the different lipophilic binders were also determined. The granule formulation was shown to be quite effective at product temperatures even below the melting point of the lipidic binder, that is, when the binder is sufficiently softened to be deformed by the very high shearing forces developed in the high-shear mixer. On the other hand the performance of lipidic binders during the melt granulation process was shown to be closely dependent on their melting and rheological properties. The granule growth rate was shown to be higher wizen the binder melting range is narrow and the influence of temperature on the viscosity of the unmelted product is high.