ABSTRACT
Dyeing textiles by traditional water-based methods demands large amounts of water. Roughly to dye 1 kg of textile 100 L of clean water are used; annually this requires 9 trillion liters of water or four times the water requirement of a country like Taiwan. At the end of the dyeing process, the same equivalent amount of wastewater is generated that needs to be treated before discharge. The dye bath effluents contain salts, bases, and hydrolyzed dye molecules, which make water purification expensive. For the last 25 years, scCO2 has been developed as an alternative to water as a dyeing medium to eliminate and reduce the usage of water and wastewater production in the conventional textile dyeing industry. The physical properties of scCO2 with regard to high diffusion rates and low mass transfer resistance facilitate the penetration of the dye into the textile,
decreasing dyeing times. Since no water is use, the drying of the textile is not necessary, saving a large amount of energy. Dyes are dissolved in the scCO2 and can be reused as is the CO2. Nowadays, supercritical dyeing of polyester is commercially available. Several years of equipment engineering and process development have been crystallized in industrial supercritical dyeing machines. This development has opened up a sustainable way of textile dyeing that will be followed soon by natural textiles such as wool and cotton on a commercial scale. In this chapter the state of the art and applications of supercritical textile dyeing are described. 17.1 Introduction
17.1.1 The Conventional Textile-Dyeing ProcessIn 2012 the textile industry produces 82 million tons of fibers, of which 61% are synthetic fibers and 39% are natural fibers. Approximately 70% of the synthetic fiber is polyester, while cotton dominates the natural fibers with approximately 80% (Fig. 17.1).
