Cotton Cationization and Dyeing in One Bath: A Short-Process, Salt-Free Approach for Reactive Dyes.

To promote the sustainable development of the textile industry and address the critical challenges of high water consumption and salt pollution in cotton dyeing, this study developed a short-process cationic dyeing method using 2,3-epoxypropyltrimethylammonium chloride (GTA). Unlike traditional cationic dyeing, this approach eliminates the intermediate drying step by adding reactive dyes directly into the same bath after modification, achieving salt-free dyeing and significant water savings. The effects of key parameters, including GTA concentration, NaOH concentration, modification temperature and time, dyeing bath ratio, holding time, and dyeing temperature, were systematically investigated. The optimal dyeing conditions for C.I. Reactive Red 195, Reactive Black 5, and Reactive Blue 19 were determined as follows: GTA concentration of 40 g/L, NaOH concentration of 1 g/L, modification at 90 °C for 50 min, dyeing at 60 °C with a bath ratio of 1:15, and holding times of 30, 20, and 40 min, respectively. After modification, thermal stability and crystallinity decreased slightly (from 60.51% to 58.18%), while hydrophilicity showed no significant change. This short-process cationic dyeing method saves time, energy, and water while maintaining dyeing performance comparable to conventional methods. It provides a practical and sustainable new approach for salt-free cotton dyeing.