Dye uptake and partition ratio of disperse dyes between a PET yarn and supercritical carbon dioxide

The equilibrium uptake of three disperse azoic dyes in a commercial PET yarn in presence of supercritical carbon dioxide was measured. The dye uptake was found to be much more sensitive to temperature than to pressure in the tested operative conditions. The equilibrium partition coefficient between the fibre and the supercritical fluid was evaluated from previously measured solubility data [A. Ferri, M. Banchero, L. Manna, S. Sicardi, An experimental technique for measuring high solubilities of dyes in supercritical carbon dioxide, J. Supercrit. Fluids 30 (2004) 41; A. Ferri, M. Banchero, L. Manna, S. Sicardi, A new correlation of solubilities of azoic compounds and anthraquinone derivatives in supercritical carbon dioxide, J. Supercrit. Fluids 32 (2004) 27]. The high values of the partition coefficients demonstrated that the partition of the dye between the fluid and the polymer is an important parameter to evaluate the feasibility of the dyeing process in supercritical carbon dioxide.The partition coefficients were correlated with three equations: an equation proposed by Funazukuri et al. with four fitting parameters [Ind. Eng. Chem. Res. 41 (2002) 2812]; a semi-empirical equation, with five fitting parameters, that was developed assuming a Langmuir-type absorption of the dyes into the yarn; and an empirical equation, with three fitting parameters, developed from simple experimental data observation. The best agreement was obtained with the second, semi-empirical equation. Good results were also obtained with the third, empirical equation and the agreement with experimental data was better than that obtained with the equation proposed by Funazukuri et al. even though it makes use of one fitting parameter less.