Experimental Characterization and Modeling of Twin-Screw Extruder Elements for Pharmaceutical Hot Melt Extrusion

In this study we characterized various screw elements of a co-rotating twin-screw extruder used for pharmaceutical hot melt extrusion (HME) and measured the pressure characteristic, i.e., the correlation between the axial pressure gradient and the material throughput in a completely filled screw section at different screw speeds. A typical HME matrix material, Soluplus, was used for the experiments and its required rheological properties were determined. A three-parameter model based on a dimensionless formulation of the measured quantities was used. These parameters could not be determined uniquely by fitting to experimental data. Therefore we developed an approach to approximate one empirical parameter based on the mechanistic consideration of a pressure-driven channel flow. The model was extended to account for the variable melt temperature. The results confirmed the expected tendencies and established an essential input parameter set for one-dimensional simulations of co-rotating twin-screw extruders.