Modeling Devolatilization in Single- and Multi-Screw Extruders

Vacuum-vented single- and multi-screw extruders are widely used to remove undesirable residual volatile components from highly viscous polymer melts. To guarantee a smooth separation process and to increase devolatilization efficiency, screw channels in the extraction section of vented extruders are only partially tilled. In the governing flow field, volatile components evaporate from the rotating melt pool that develops in front of the active flight flank and from the wiped melt film deposited on the extruder barrel. This paper investigates mass transport phenomena in the rotating melt pool in detail. Based on numerical methods, the flow field in the melt pool is calculated and related to Fick's laws of diffusion. The course of volatile concentration in the melt pool is analyzed taking the circulatory motion of the melt pool into account, and the beneficial impact of surface renewal on devolatilization efficiency is elucidated.