DRYING POLYMERS DURING SCREW EXTRUSION

Partial removal of dissolved or absorbed solvent from polymers can be accomplished during the process of screw extrusion. This paper shows how two simple transport models based either on an effective diffusivity or on an empirical mass transfer coefficient can be combined with the fluid mechanical equations which describe polymer flow during screw extrusion. In this way, the drying of solvent from a polymer during extrusion can be correlated in terms of the design and operating parameters of the extruder screw and a mass‐transfer coefficient or an effective diffusivity. This approach is illustrated employing data obtained by using two extruders of different size and two different solvent‐polymer systems. Furthermore, it is pointed out how the results can be used to predict the extent of drying during screw extrusion as well as how modifications in extruder‐screw design can permit more extensive drying of polymers during the extrusion process. Copyright © 1969 American Institute of Chemical Engineers