Environmentally friendly method in reactive dyeing of cotton

Abstract

The recipe for reactive dyeing of cotton can be divided into three steps: the pretreatment, the dyebath and the final rinse. The consumption of chemicals and water in the rinse has been found to be considerable: three quarters of the total COD discharge of the recipe have relations to auxiliary chemicals used and three quarters of the total water consumption have relation to the rinse. The improvement potential in the rinsing procedure were found to be considerable, and the newly developed recipe focuses on improvements in the rinse. Tests with the new recipe have documented that neutralization, detergents and complexing agents can be left out completely with no adverse effect on product quality. All recognized tests of fastness and shade have been performed and evaluated in cooperation with the dyehouses. More than 50 full-scale dyeing experiments have been carried out in jets, overflow and drum batch machines. The experiments include 25 different reactive dyestuffs, among these azo, anthrachinon, phtalocyanin and formazan dyestuffs, including both monoreactive and bireactive dyestuffs of which 15 had the vinyl sulfone as reactive group. The dyestuffs have been combined in 20 different recipes covering very light to very dark shades. Hot membrane filtration of the hot rinsing water has been investigated in parallel projects and it is documented that membrane filtration saves chemicals, water and production time, and also gives large energy savings in one new recipe.