A novel design for hot-melt extrusion pelletizers

Abstract

In this work we investigated a novel die design for the scale-up of hot melt extrusion (HME) devices for direct pelletization of pharmaceutics. Therefore we analyzed the temperature distribution in a lab- and production-scale die as well as melt flow through the die. Finally we explored the possibilities of an inner rotating knife for stabilizing melt flow. The work was based on computational fluid dynamics for simulating non-Newtonian melt flow and corresponding temperature fields. The results show that a tight temperature control of the die material is necessary to guarantee a safe scale-up of the process. Even in lab-scale applications temperature inhomogeneities have been observed both experimentally as well as in the simulation. These inhomogeneities act as an trigger to destabilize melt flow and hence could lead to a shutdown of the process. The proposed inner rotating knife acts as a pulsating device and consequently is able to enhance process stability. However, due to heat dissipation in the small gap between rotor and stator, this device has to be fitted with a separate low-speed drive and cannot be coupled directly to the main extruder shaft.