SIMULTANEOUS VISCOSITY AND DENSITY-MEASUREMENT OF SUPERCRITICAL CO2-SATURATED PEG-400

In order to analyse the effect of supercritical fluid (SCF) addition o n polymer viscosity we have used, for the first time, a high precision vibrating wire instrument, for the simultaneous measurement of viscos ities and densities of a SCF-saturated polymer. For the density measur ements, this technique makes use of the buoyancy force exerted by a fl uid on a solid sinker, detected by means of a vibrating wire sensor pl aced inside the measuring cell. The viscosity and density of the fluid are obtained by analysis of the resonance curve of the vibrating-wire , using a rigorous model for describing the hydrodynamic effects of th e fluid on the wire motion. Results of the preliminary measurements ca rried out on a commercial linear thermoplastic oligomer [Poly (ethylen eglycol) 400] saturated with CO2 are presented, in a range of temperat ures from 313 to 348 K (3 isotherms) and at pressures up to 25 MPa. A sharp decrease of the viscosity was observed for all temperatures. The highest viscosity reduction was reached at the lowest temperature. (C ) 1998 Elsevier Science B.V.