Sustainable Cotton Dyeing in Nonaqueous Medium Applying Protic Ionic Liquids

Dyeing processes are highly important for differentiation of textile products, and in general, they use a huge amount of water and chemical additives, generating a great environmental impact. In the last years, the interest in finding alternative environmentally friendly solvents for these processes has increased, with a double aim: to decrease the quantity of water used and to improve the dyeing quality. In this work, we analyze an alternative procedure to dye cotton fabrics with only two dyeing agents, a polyfunctional reactive dye and a protic ionic liquid (PIL) as an alternative solvent, avoiding the need for common chemical additives into the conventional process, thus reducing the amount and concentration of pollutants. The proposed procedure allows PIL recycling with no appreciable loss of efficiency, since after dyeing, the unfixed dye remains active in the bath, following the known exhaustion dyeing method. A collection of 13 PILs were studied with the aim of analyzing their effectiveness as dyeing solvents in terms of different standard dyeing quality parameters such as absorption color, tensile strength, and surface morphology of the cotton dyed. The results obtained using PIL as dyeing solvents in the absence of any auxiliary agent showed an outstanding effect when compared with the aqueous process under the same operational conditions.