MODELING POLYETHYLENE SOLUTIONS IN NEAR AND SUPERCRITICAL FLUIDS USING THE SANCHEZ-LACOMBE MODEL

Effectiveness of the Sanchez-Lacombe model in predicting the high pres sure phase behavior of solutions of polyethylene standards of molecula r weights 2,150, 16,400, 108,000, and 420,000 in n-pentane and n-penta ne-carbon dioxide binary solvents has been evaluated. It is shown that by proper adjustment of the characteristic temperature for the polyme r, which is achieved by using data for one molecular weight sample, va riations with respect to concentration and pressure are correctly pred icted. The model correctly predicts also the solvent-dependent shift f rom LCST (Lower Critical Solution Temperature) to UCST (Upper Critical Solution Temperature) type behavior for these solutions upon increase in. the carbon dioxide content of the n-pentane-carbon dioxide binary solvent.