JOURNAL OF POLYMER ENGINEERING

 Vol. 23, No. 1, 2003, page 1

Rheological properties of polystyrene/supercritical CO₂ solutions from an extrusion slit die

  Anle Xue and Costas Tzoganakis*

 Department of Chemical Engineering

University of Waterloo

Waterloo, Ontario, Canada, N2L 3G1

 Revised August, 2002

  Abstract

       Recent advances in the use of supercritical CO₂ (scCO₂) in polymer processing (i.e. injection molding and extrusion) have increased the need for rheological data of polymer/scCO₂ 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/scCO₂ solution. Dissolution of CO₂ 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/CO₂ 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 CO₂ concentrations. Shear viscosities of PS as well as PS/CO₂ were described using the generalized Cross-Carreau model and the Doolittle equation and different free volume models were compared.

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