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Supercritical dyeing can be an interesting alternative to traditional dyeing due to the unquestionable advantage of the use of a clean solvent that can be easily recovered and separated from the excess dye at the end of the process. The experience achieved by our research group during a research project supported by the Italian government is reported in this work. The aim of the project was to set up a pilot plant where supercritical dyeing could be performed with yarn bobbins. In particular, this work shows the results obtained for polyester textiles. In the first part of the project, laboratory scale experiments were performed to determine the equilibrium partition of each dye between the two phases. In the second part, the pilot plant was set up. The dyeing results were successful: good reproducibility, together with a good dye uniformity and fastness (comparable with that of the traditional process) were obtained. The maximum productivity of the pilot plant is about 5 kg/h and the total duration of the dyeing process (approximately 1.5 h) is much shorter than that of the tradional method (3-4h). [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Supercritical dyeing has risen good expectation in the last few years due to the attractive perspective of complete elimination of water from dyeing processes. A lot of research activities have been developed in the last decade both to deepen the knowledge of the interaction mechanisms between CO2, dye and polymers and to solve the technological problems of the process set-up. Among the last ones that of a non-uniform dye distribution when a yarn package is subjected to dye impregnation is one of the most undesired. The same problem is usually faced in the industrial practice of traditional aqueous dyeing and has always been solved empirically. Aim of the present work is to propose a simple model that simulates the dyeing process of a spool of yarn both with the aqueous and supercritical techniques pointing out the main characteristic times and allowing calculation of dye concentration profiles both in the dyeing ‘bath’ and along the yarn spool. The analysis of the influence of characteristic times ratios gives some indications on the best operative conditions that should be attained to guarantee an uniform dye distribution along the package radius both for aqueous and supercritical dyeing; the two processes, in fact, mainly differ for the order of magnitude of the characteristic times. To support the discussion arisen from the different roles of characteristic times on the model, a practical example of supercritical dyeing simulation is also performed for a specific PET package with a disperse dye already used in the literature at well defined working conditions. [Copyright &y& Elsevier]