The production of homogeneous extrudates of microcrystalline cellulose pastes.

The homogeneity of water-based microcrystalline cellulose (MCC) paste extrudates was investigated during ram extrusion as a function of ram velocity. Variations in the water content of the extrudates were caused by liquid phase migration within the paste. The evolution in water content was measured by sectioning and drying the extrudate, and the subsequent homogeneity was quantified by the standard error in water content. The homogeneity of the extrudates was found to decrease as the ram velocity decreased. This result was also inferred from the rate of increase of the extrusion pressure. The extrudate homogeneity was significantly improved by compensating for water migration in the barrel during the compaction stage. This was achieved using a non-uniform initial paste billet, created by packing the barrel with layers of paste of different water contents. This technique also produced a smaller variation in extrusion pressure over the ram displacement range, and a reduction in water loss from the upstream paste compact into the extrudate and/or through the apparatus tooling.