Study on the salt-free low-alkaline reactive cotton dyeing in high concentration of ethanol in volume

To achieve salt-free and low-alkaline reactive cotton dyeing, ethanol-water mixture with high concentration of ethanol in volume was employed as medium for cotton fabrics dyeing by reactive dyes. The influence of ethanol concentration and wet pickup of pre-swollen cotton fabric on both water and ethanol contents in the fabric, dye exhaustion and fixation rates were investigated, and the effect of ethanol concentration and alkali dosage on the alkali content in pre-swollen cotton fibers were also investigated. The dyeing properties in ethanol-water system was also compared with that in conventional aqueous system. The results indicated that both ethanol concentration and wet pickup were important factors influencing water and ethanol contents of pre-swollen cotton fabrics and ultimately dye exhaustion and fixation. The percentage of alkali on the fabric in ethanol-water system was much higher than that in conventional aqueous system, and can be controlled by the ethanol concentration and the alkali dosage. It also can be concluded that the optimum condition was pre-swollen cotton fabrics with 40% wet pickup dyed in ethanol-water system with 80 vol% of ethanol. The dyed sample under the optimum condition had higher K/S value and levelness than the water-dyed sample, and its dry and wet rubbing fastnesses were found similar or acceptable in comparison with the water-dyed sample. More importantly, no electrolytes had been used in our ethanol-water system and the alkali dosage was one fifth of that in conventional aqueous system, contributing to the environmental benefits of ethanol-water system. (C) 2019 Elsevier Ltd. All rights reserved.