A comparison of screen and ram extrusion–spheronisation of simple pharmaceutical pastes based on microcrystalline cellulose

The performance of two laboratory-scale extrusion apparatuses used to approximate the action of an industrial screen extruder, namely a multi-holed die ram extruder and a roller screen extruder, were compared. Both devices featured short dies (ram 2 mm, screen 1 mm) with die diameter 1 mm and hole area fraction approaching 0.25. A series of water/microcrystalline cellulose (MCC) pastes with water contents varying from 45 to 60 wt% were extruded and pellets obtained from subsequent spheronisation of the extrudates characterised in terms of size and shape. Each device exhibited a different range of processing windows for acceptable spheronised products, with the ram apparatus being able to extrude a wider range of paste water contents than the screen device. The pellets obtained from extrusion–spheronisation (E–S) of the pastes via the screen device were in general smaller, with a wider size distribution, than those from ram E–S. These results are attributed to the different mechanical histories experienced by the pastes in the two types of extruder, which lead to different extrudate densities being achieved. MCC/water/calcium carbonate pastes were also tested, where the latter component represented a ‘hard’ (non-deformable) active pharmaceutical ingredient. Addition of calcium carbonate increased the stiffness of the paste, which could be countered by adjusting the water content of the deformable MCC/water matrix within the extrudability limits of the latter material.

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