Foaming indigo: An efficient technology for yarn dyeing

The global production of denim fabric is more than 9 billion meters, and indigo dye, an essential dye in the denim field, uses about 30–50 tons of water per million meters in the washing process after dyeing in order to remove the floating color. At present, the most common cotton yarn dyeing process is the traditional process of dyeing, using the multi-vat immersion dyeing method of the assembly line. In order to successfully reduce the water and energy consumption with the foaming process, it is necessary to combine the foam system by indigo reduction method. This study through the foam system selection and process optimization,The results showed the concentration of sodium dodecyl sulfate is 3 g/L, the concentration of citric acid is 1.2 g/L, the temperature is 50 °C, the speed is 1200r/min, and the stirring time is 5min. A simulated factory yarn-dyeing line was built, Through orthogonal test, sodium Hydrosulfite concentration and sodium hydroxide concentration required for 5 g/L indigo reduction were 7 g/L and 3 g/L, respectively. When the temperature was 80 °C, the reduction effect of indigo was the best. Taking the K/S value of cotton dyed with 5 g/L traditional process as the control, the required concentration of indigo dye foaming process was determined to be 14 g/L at 50 °C, and the foam indigo foaming technology was realized. By comparing the twist, single yarn strength, and hairiness tests of the dyed cotton yarn with the two technology, the results showed that the properties of the dyed cotton yarn with the foam indigo technology dye are better than the traditional technology. Compared with traditional technology, foam technology saves about 53.5% water and has an efficiency ratio of 1:10.