A comparison of two methods of instrumenting a small-scale basket extruder

A comparison of ram extrusion by single-holed and multi-holed dies for extrusion-spheronisation of microcrystalline-based pastes

The use of multi-holed dies as an alternative to single-holed dies for generating extrudates for spheronisation was investigated both in terms of extrusion and spheronisation performance. A model 45wt% microcrystalline cellulose (MCC)/water paste was employed in ram extrusion tests with square-ended dies with 1, 6, 33 and 137 holes, all of diameter 1mm and length 2mm. The extrudates generated using the multi-holed dies yielded pellets with comparable sphericity to those using the single-holed die. Multi-holed dies could also be operated with lower paste flow rates before encountering liquid phase migration (LPM). The characteristic processing velocity for the onset of LPM was determined for each die configuration and supported the hypothesis that LPM was caused by suction effects. A simple model of the flow pattern in a lab-scale Fuji-Paudal frontal screen extruder is presented which yields estimates of velocities and shear rates involved in these devices. The pressure required to extrude the paste through multi-holed dies was compared with the model proposed by Benbow and co-workers. The paste rheology was characterised using the Benbow-Bridgwater approach, employing 1, 2 and 3mm diameter dies of various lengths. The Benbow et al. model under-predicted the observed extrusion pressure, which was attributed to its failure to account for the redundant work contribution in these complex flows.

Characterization of wet masses of pharmaceutical powders by triaxial compression test

The mechanical and rheologic properties of wet masses of pharmaceutical powders determine their processibility and the quality of the product prepared by extrusion/spheronization. In this work, a triaxial compression test was attempted for the first time to characterize material properties of pharmaceutical wet masses of different hydrophilicity and particle sizes. The stress-strain curves and the pore pressure were determined at various cell pressures. The failure criteria of the wet masses were obtained from the stress path on the deviator stress plane. The cohesion (c) and the angle of internal friction (phi) were evaluated from the intercept and the slope of the failure loci. The stress-strain behavior strongly depended on the type of powders and cell pressure. The values of c and phi were similar for wet masses of EC FP, MCC PH101, and SMCC 50, but a very small phi and a very high c value for HPMC. The shear strength and rigidity of the wet masses were in the order of EC FP > SMCC 50 > MCC PH101 > HPMC, whereas the elastic recovery was in the opposite order. These material parameters could be used as references for selection of excipients and formulation for extrusion/spheronization.