MELT PELLETIZATION IN A HIGH-SHEAR MIXER .4. EFFECTS OF PROCESS VARIABLES IN A LABORATORY-SCALE MIXER

Melt pelletization of lactose in an 8 litre high shear mixer was examined by a factorially designed experiment. Polyethylene glycol (PEG) 3000 was used as melting binder in a concentration of 23% m/m. The load of the mixer was varied at 600, 800 and 1000 g of lactose. Effects were investigated of: massing time, impeller speed and mixer load on mean granule size and size distribution, amount of lumps, intragranular porosity, adhesion of material to the bowl, product temperature and power input. The process was found to be the most reproducible and to give rise to the optimum pellets at a mixer load of 1000 g. A lower mixer load gave rise to a larger amount of lumps. The highest impeller speed resulted in the largest and most rounded pellets. The agglomerate growth was found to be dependent on the power input.