Sustainable Production by Modifying Reduction Clearing in Polyester Dyeing

Conventional reduction clearing of dyed polyester fabric is carried out by using the sodium dithionate under strong alkali conditions. Technical issue is the sensitivity of sodium hydrosulfite to air oxidation in an alkaline medium at high temperature, so that an excess is used to compensate for the loss. In our present study, non-ionic ethoxylated surfactants, as separate and in combination, with different HLB values have been used for wash-off process. Fatty alcohol ethoxylated surfactant and castor oil ethoxylated surfactant with different HLB 9–17 as separate compound and in combination has been used for wash-off process at different pH range (4.5–12 pH), time (5–20 min) and temperature (50–100 °C). Our findings indicate that surfactant can be efficiently used in neutral pH to replace the sodium-dithionate-based reduction-clearing process in the polyester dyeing. Thereby, eliminates the pH adjustment after dyeing from acidic to strongly alkaline condition. Surfactant blends with all HLB value give better results than individual surfactants. Our study results confirmed better color fastness properties and delta E of the fabric <1 with surfactant wash-off process. Also, the effluent load in terms of TDS (96%) and BOD and COD (30–40%) has been reduced. And the use of caustic lye to adjust pH and sodium dithionate for reduction-clearing process is completely eliminated. Therefore, wash-off treatment of polyester by surfactants emphasizes the substantial energy and chemical savings as well as lower environmental impact than traditional process.