Imidazolium-Based Ionic Liquids as Auxiliaries for Aqueous Disperse Dyeing of Polyethylene Terephthalate

The aim of this study was to develop a method to dye polyethylene terephthalate fabrics to light and medium shades at 95 °C without the use of carriers, dispersing agents, or reducing agents and to evaluate the effectiveness of monocationic and dicationic ionic liquids as auxiliary chemicals in the dyebath. Four ionic liquids were employed: 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1,4-bis(3-methylimidazolium)butane dibromide, and 1,4-bis(3-methyl imidazolium)butane dichloride. Dye exhaustion increased from 31.5% in the IL-free control sample to 88.4% in the presence of 10 g/L of the dibromide-based dicationic ionic liquid. Although different crystallinity values were obtained using different analytical techniques, both methods indicated lower crystallinity in the corresponding dyed sample than in the control. Considering the nonlinear nature of polyethylene terephthalate fabric dyeing, machine learning models were employed to predict color strength based on ionic liquid type, concentration, and measured color coordinates. The models’ performance was evaluated using five-fold cross-validation and complementary statistical metrics. Shapley Additive Explanations analysis was employed to interpret the contributions of input variables to model predictions. The results identified ionic liquid concentration and type as the most influential features in the selected model, followed by colorimetric descriptors.