Controlling the structure of a porous polymer by coupling supercritical CO 2 and single screw extrusion process

A study on the extrusion of Eudragit E100 was carried out using supercritical carbon dioxide (scCO 2 ) as plasticizer and foaming agent. ScCO 2 modifies the rheological properties of the material in the barrel of the extruder and acts as a blowing agent during the relaxation when flowing through the die. For experiments, a single‐screw extruder was modified to be able to inject scCO 2 within the extruded material. The aim is to determine a correlation between operating conditions and foam structure. The effect of three parameters was studied: the temperature in the die and in the metering zone, the screw speed, and the volumetric flow rate of CO 2 . An increase in temperature enhances the expansion rate and the average pore diameter and appears to be the most significant parameter. The effect of CO 2 concentration is significant at small concentrations only: the higher the CO 2 concentration, the lower the pore density and the higher both the pore diameter and the expansion rate. The effect of the screw speed is tricky because a variation of this speed involves a decrease of CO 2 weight ratio. This study shows that the structure of the extrudates does not evolve with a coupling of screw speed increase and a subsequent CO 2 weight ratio decrease. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010