Equilibrium Study on the Disperse Dyeing of Polyester Textile in Supercritical Carbon Dioxide

The dyeing of polyester textile in supercritical carbon dioxide (scCO₂) was investigated experimentally. The influence of temperature and density of the scCO₂ on the process was studied in the ranges 85—125°C and 400—550 kg/m³. The dye saturation concentration in the polyester increased and the distribution coefficient decreased with temperature, the latter showing a logarithmic dependence on the reciprocal of temperature. Increasing the fluid density led to an increasing saturation concentration and a decreasing distribution coefficient. When the right temperature and solvent density were chosen for the supercritical process, the same dye concentration could be attained as in aqueous dyeing. It was found that the adsorption of the dye on the polyester followed Nernst adsorption, as is the case in aqueous dyeing. The experiments showed that the dyeing was exothermic, with a negative change of entropy. The thermodynamic characteristics of supercritical and aqueous dyeing were concluded to be roughly the same, with similar saturation concentrations, thermodynamic affinities and heats and entropies of dyeing.