Solubility and diffusivity of supercritical carbon dioxide in cellulose acetate with cosolvents

The gravimetric procedure was applied to investigate the solubility and diffusivity of supercritical carbon dioxide (SC-CO2) in cellulose acetate (CA). The solubility increases constantly in the initial period and reaches the dissolution equilibrium when the saturation time exceeds 10 h. The solubility decreases gradually from 14.29 wt% to 7.36 wt%, while the saturation temperature increases from 40 degrees C to 70 degrees C. The solubility increases by only 5.63%, while the saturation pressure grows from 10 MPa (12.62 wt%) to 30 MPa (13.33 wt%). The presence of cosolvents, especially ethanol, improves the solubility obviously. The diffusivity is not affected by pressure but increases with the solubility. Scanning electron microscopic images show that the cell densities increase with the content of ethanol, which implies that the higher solubility is in favor of the cell nucleation. The foamed CA with 10 wt% or 20 wt% ethanol has both low density and good impact properties.