Miscibility, viscosity and density of poly (ɛ-caprolactone) in acetone + CO 2 binary fluid mixtures

Abstract

High-pressure viscosity and density of poly (ɛ-caprolactone) (PCL) (Mw = 14,300; Mw/Mn = 2.34) solutions in acetone and in acetone + CO 2 mixtures have been determined over a temperature range from 323 to 398 K and a pressure range from 7 to 35 MPa. The effect of adding CO 2 on viscosity was investigated for the 5 wt% solutions at CO 2 concentrations of 1, 2, 4 and 40 wt%. The effect of phase separation on viscosity was studied for the 5 wt% polymer solution in the binary fluid mixture with high (40 wt%) carbon dioxide content. The solution viscosities ranged from 0.2 to 0.6 mPa·s with flow activation energies in the range 7–9 kJ mol −1 and flow activation volumes in the range from 12 to 29 cm 3 mol −1. Close-packed volumes estimated from correlation of the data to Doolittle equation were in the range 0.5–0.6 cm 3/g. In ternary solutions containing carbon dioxide, solution densities were higher, reflecting the higher density of compressed CO 2 compared to that of acetone, but viscosities were lowered. A viscosity reduction of about 50% was observed with 40 wt% CO 2 addition. The density and viscosity data for the PCL solutions have been compared with data for solutions of poly (methyl methacrylate) (PMMA) with similar molecular weight in acetone + CO 2. The results show that the acetone + CO 2 binary mixtures are “better” solvents for PCL than PMMA.