Abstract
Recent advances in the use of supercritical CO 2 (scCO 2 ) in polymer processing (i.e. injection molding and extrusion) have increased the need for rheological data of polymer/scCO 2 solutions at high pressures. In this study, a slit die with a sudden contraction was used to investigate the entrance pressure drop as well as the shear and extensional viscosities of a polystyrene (PS) melt and of a PS/scCO 2 solution. Dissolution of CO 2 into the PS melt was shown to reduce its entrance pressure drop as well as its shear and extensional viscosities. The entrance pressure drop of PS and PS/CO 2 was found to be a strong (exponential) function of pressure. The entrance pressure drop as a function of wall shear stress could be fitted with a master curve for all experiments at different temperature, pressure and CO 2 concentrations. Shear viscosities of PS as well as PS/CO 2 were described using the generalized Cross-Carreau model and the Doolittle equation and different free volume models were compared.
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