Dyeing of PET Fibers in Ionic Liquids

Klaus Opwis, Rainer Benken, Dierk Knittel, Jochen Stefan Gutmann

The dyeing of textile materials is still accompanied with several economic and ecological disadvantages resulting in a high consumption of water, energy and chemicals. In particular the dyeing of polyester fibers (PET) - beside cotton the most important fiber type - is accompanied with additional disadvantages, because it needs high process temperatures of more than 130 °C enabling the disperse dye stuffs to penetrate the fiber matrix above the glass transition temperature of PET. Therefore, an aqueous dyeing liquor would evaporate if open systems were used. Due to this, in praxis the dyeing of PET fibers is carried out in special pressure vessels, which results in another cost intensive factor. Thus, since many years textile researchers around the world are looking for alternative dyeing techniques for all kind of fiber types but especially for PET. In this context, ionic liquids (IL) can play an important role. IL are salts with a melting point lower than 100 °C and they are often thermo-stable far beyond 200°C. IL excel by their extremely low vapor pressure, which makes them easy to handle in contrast to typically used organic solvents. Moreover, IL show high and temperature related dielectric constants, therefore showing outstanding solvent power for different textile-related substances, such as cellulose, keratin, and silicones. In addition, preliminary work at DTNW has shown that IL are suitable as dyestuff medium for textiles (e.g. for disperse dyestuffs, cationic dyestuffs, reactive and metal complex dyestuffs). Now, the DTNW has developed an innovative operational technique to dye various fibers in IL. This has been systematically investigated for the commercially most important fiber PET. Our dyeing procedure allows a pressure-free dyeing at high temperatures with minimal air pollution, which enables the textile industry in future to carry out their business with new methods avoiding high consumption of energy, water and chemicals.