Modeling of residence time distributions of twin-screw extrusion processes considering various screw types

Abstract

Residence time in pharmaceutical hot-melt extrusion is a crucial process parameter affecting the quality attributes of a dosage form such as content uniformity, bioavailability and toxicity. There is a lack of knowledge about the influence of screw element types on the residence time distribution, which will be addressed in this study. Methods: Different conveying and kneading elements will be characterized concerning their effect on the residence time using a co-rotating twin-screw extruder with a 28 mm screw diameter. Tracer experiments will be performed while concentration time profiles are measured via inline UV-Vis spectroscopy. Results: The residence time distribution of all screw types is primarily related to the volume flow but independent of pressure. The two-compartment model of Reitz was utilized to describe the experimental data mathematically. Screw-type-specific dimensionless parameters were derived to quantify the axial mixing performance, as well as the effect on residence time. Conclusions: The influence of different screw elements on the residence time in hot-melt extrusion processes was quantified using a dimensionless mixing volume and a dimensionless axial dispersion coefficient. The results meet the quantitative descriptions from the literature.