Analysis of extrusion of some wet powder masses used in extrusion/spheronisation

The extrusion how behaviour of mixtures of lactose, microcrystalline cellulose (MCC) and water in the ratio 5:5:6 by weight has been analysed from data previously obtained by a ram extruder for powder and colloidal grades of MCC. The analysis followed a recent approach of examining the viscous and elastic behaviour of polymers. Results suggest that at low how rates, mixtures containing colloidal grades of MCC have significantly higher shear viscosities than powder grades. The present analysis also shows that shear thickening of some mixtures occurs. Elongational how was also examined together with entry flow to the die. The results of the analysis indicate that: (a) particle size of the MCC is not important, (b) the greatest extrudate distortions occur for systems having relatively low shear viscosities at low flow rates. There appears to be an optimal elasticity for the formation of satisfactory spheres in the spheronisation stage, i.e. they must neither be too elastic nor have low elasticity.