Single box dyeing of denim yarns under nitrogen protection with high indigo concentration

Abstract

In the era of “double carbon,” green short process preparation of denim textiles will become more and more popular, and dyeing is an essential step in this process. In order to improve dye utilization and energy efficiency, a high-concentration indigo single box dyeing method based on nitrogen (N2) protection has been studied. The optimal dyeing conditions were obtained. The dyeing mechanism was revealed by evaluating the stability of the dyeing solution and dye distribution in the dyed yarns. Various dyeing properties, chemicals, energy consumption, and dyeing wastewater were measured and compared with conventional slasher dyeing. It has been shown that N2 protection effectively avoids the oxidation of soluble leuco-indigo and improves the stability of the leuco dyeing bath. In addition, the dyes diffused more deeply into the fiber in the dyeing box under a micro-positive pressure environment, enhancing the dyeing efficiency and depth. The proposed technique exhibited better dye utilization and excellent color fastness. Dyeing wastewater was more chemical and biodegradable, relieving wastewater treatment. Generally, cleaner dyeing not only reduces the consumption of energy, water, and chemicals, but also saves 46.8% of the economic cost compared with traditional slasher dyeing, indicating that the proposed technology is interesting for industrial application.

Vat Dye Molecule–Proton Dual Adsorption Catalysis Based on Molybdenum Disulfide for Sustainable Textile Dyeing

“…Based on current industrial practices, the dyeing process for indigo denim fabric consumes approximately 2 t of the toxic and corrosive Na 2 S 2 O 4 per ton of fabric, with an estimated 60−70% of this amount being discharged into the environment. 16 This significant chemical discharge not only imparts severe contamination to aquatic ecosystems but also exerts enduring detrimental effects on soil integrity and the broader ecological balance. 17 Therefore, the development of indigo dye reduction processes that eliminate the reliance on toxic reducing agents is essential for advancing the sustainable practices within the textile industry.…”

“…As a symbol of a free lifestyle, denim fabric and clothing have consistently been beloved by global consumers, with an annual global production exceeding an astonishing 9 billion meters and a value exceeding 25 billion USD. − However, the production process of denim garments, particularly the dyeing stage, has caused significant environmental pollution. − This pollution is primarily due to the excessive use of indigo dyes and reducing agents, such as sodium dithionite (Na 2 S 2 O 4 ), during the dyeing process. Based on current industrial practices, the dyeing process for indigo denim fabric consumes approximately 2 t of the toxic and corrosive Na 2 S 2 O 4 per ton of fabric, with an estimated 60–70% of this amount being discharged into the environment . This significant chemical discharge not only imparts severe contamination to aquatic ecosystems but also exerts enduring detrimental effects on soil integrity and the broader ecological balance .…”