Supercritical dyeing of textiles - from the laboratory apparatus to the pilot plant

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—4 h).