Significance Although dyeing is an important technique to give color to textiles, it also depletes resources and creates a lot of pollution. Reactive and disperse dyes are the most widely used dyes for coloring cellulose and polyester fibers, respectively. The output of two dyes accounts for more than 70% of the total output of dyes. However, reactive dyeing has problems with insufficient dye utilization, excessive use of inorganic salts, and high wastewater discharge. Meanwhile, the reduction cleaning step in the disperse dyeing process uses a lot of water and energy. The dispersants and unfixed dyes which are washed off in the reduction cleaning step will cause more difficulty in treating wastewater. Therefore, innovative dyeing techniques of two dyes that can solve these problems were reviewed in this paper. Progress In order to reduce the usage amount of inorganic salts in reactive dyeing technology, researchers developed a series of methods to increase the affinity of dyes and fibers, such as cationic modifications and designing macromolecular dyes. In order to improve the utilization of dyes, the wet pickup of the fabric was controlled at a low level to reduce the hydrolysis of reactive dyes. The low wet pickup dyeing technologies are foam dyeing, vacuumdewatering aided pad-steam dyeing, spray dyeing and ″moisture fixation″ dyeing. Organic solvent (ethanol, decamethylcyclopentasiloxane, silicone oil) /water mixed solvent, liquid ammonia, and organic mixed solvent (dimethyl sulfoxide/dimethyl carbonate) were used as dyeing media to reduce the wastewater discharge. In order to solve the problem of low dyeing efficiency and high material consumption of rope dyeing, open-width dyeing technology for the cotton knitted fabric was developed. For disperse dyeing techniques, the first advancement is the development of alkali-resistant disperse dyes, which were created to solve the problem of water and energy usage during the reduction cleaning process. Owing to the same alkaline conditions, the pre-treatment and soap-washing procedures can also be combined with alkaline dyeing technology to increase production effectiveness. Secondly, the polymer dispersants with low molecular weights, no matter the synthesized copolymer anions or modified biomass polymers, were designed to make the dyes maintain nanoscales in water by grinding. Thus, the nano-scale liquid disperse dyes were prepared to improve the dyeing uptake and reduce loose color. With the use of microcapsule shells, the non-reduction clearing effect is achieved through the adhesion on the surface of the fabrics. Finally, non-aqueous media such as supercritical carbon dioxide fluid or organic solvents (decamethylcyclopentasiloxane, liquid paraffin) are used for dyeing to save water consumption. Conclusion and Prospect To sum up, the development of the two dyeing technologies focused on reducing the use of chemicals and wastewater emission, improving the utilization rate of dyes, and improving the efficiency of dyeing production. The use of reactive dyes with little or no salt has the problem of poor dyeing levelness or color fastness. For the wet pickup dyeing technology, the main direction of future research is to control the uniformity of dyeing and improve the color fixation rate to the highest level. The directions that need to be explored include the adaptability of open-width dyeing technology for knitted cotton textiles to thin fabric and the enhancement of process stability. Alkaline dyeing, nano liquid disperse dyeing and non-reduction clearing dyeing technologies have basically reached the industrial level, but it is still necessary to improve the categories of dyeable fabrics and improve the dyeing quality. It still needs to keep developing the theoretical framework and supporting equipment for less-water or non-aqueous dyeing technologies, whether they use reactive or disperse dyeing systems. In the future, reactive and disperse dyeing technologies continue to advance in a green and consumption-reduction direction, which will encourage the textile dyeing and printing industry to achieve the ″carbon dioxide emissions peak and carbon neutrality″ target as soon as feasible. © 2023 China Textile Engineering Society. All rights reserved.
