Effect of the addition of a modifier in the supercritical dyeing of polyester

The aim of the work was to investigate the effect of an ethanol addition in the dyeing of a commercial polyethylene terephthalate yarn with supercritical carbon dioxide. The equilibrium uptake in the yarn and the partition coefficients of three azo dyes between the polymer and the fluid phases were experimentally measured under different working conditions and compared with the data obtained without any modifier. It was found that the presence of the modifier increases the dye concentration in the yarn and the solubility of the dye in the supercritical phase, allowing good dyeing results to be obtained under less severe working conditions. The partition coefficient data were also satisfactorily regressed with a semi-empirical correlation, available in the literature for a different system and here adapted to the partition of a dye between a fibre and a supercritical bath.