Salt‐free reactive dyeing of cotton

Abstract

Purpose -Fibre reactive dyes are very popular for cellulosic garments as they are environmentally safe and having good overall fastness properties. But application of these dyes requires a very high concentration of salt. The salt released from garment dyeing increases salinity in drain water stream which has a negative impact on environmental ecology. The present work aims to eliminate the usage of salt during dyeing of cotton goods with reactive dyes. Design/methodology/approach -The methodology adopted here, for the elimination of salt in cotton dyeing, was based on the principle of cationisation (to develop a positive charge) of cotton. The same was achieved by subjecting the caustic pretreated cotton fabric samples to a treatment of 1, 2 dichloroethane followed by methylamine to introduce amino groups in the cellulose structure. The treated cotton when dyed from slightly acidic bath generates positive sites due to protonation in the amino group. The reactive dyes being anionic (negatively charged) in solution get attracted to the positive charges on the fibre which eliminates the salt requirements for satisfactory dye exhaustion. Findings -The investigation was conducted for cold brand, hot brand and highly exhaustive reactive dyes. The modified cotton showed excellent dye exhaustion for all the dyes in the absence of salt. The treatment was found to improve the dye fixation also. The modification was assessed through elemental analysis.Research limitations/implications -This study may be further extended to viscose material after suitably modifying the treatment conditions. Practical implications -A pretreatment to cotton which could eliminate the usage of salt in its dyeing with reactive dyes is revealed. Originality/value -The study explored a newer technique of cotton dyeing without salt usage. Both garment dyeing units and fabric/yarn finishing industries would thus be helpful.

The use of reflectance measurements in the determination of diffusion of reactive dyes into cellulosic fiber

“…24 The value can also be used to determine other important dyeing factors such as dye uptake, migration index, and dye fixation. 4,23,[25][26][27] A relation between K/S value and the crosssectional distribution of dye molecules in the dyed cellulosic fibers and yarns has been reported. 28 Based on this fact, studies were carried out for dye diffusion in pad dyeings which resulted in a new method of measuring reactive dye diffusion into cellulosic fiber using K/S values.…”

“…The K/S value has been shown to be a direct measure of the color yield . The value can also be used to determine other important dyeing factors such as dye uptake, migration index, and dye fixation . A relation between K/S value and the cross‐sectional distribution of dye molecules in the dyed cellulosic fibers and yarns has been reported .…”

Sustainable textile dyeing processes

“…Presence of highly reactive primary amino group makes dendrimers suitable for salt-free textile dyeing application. It had been shown that dendrimer pretreatment produces good colour depth even without addition of electrolytes, alkali or levelling agents (Burkinshaw et al 2000).…”

“…Most common approach of cationization of cotton is to introduce amino or ammonium groups into cotton (Burkinshaw et al 2000;Wang and Lewis 2002;Zhang et al 2007). Presence of nucleophilic compounds such as primary amines in the cationizing agent enhances dye fixation as the dye molecules can react with this nucleophilic compounds at pH lower than usual (Burkinshaw et al 2000). Amino groups can be introduced into carbon through a sequential treatment of caustic pretreated cotton with dichloroethane followed by methyl amine.…”

Salt-free reactive dyeing of cotton hosiery fabrics by exhaust application of cationic agent

“…The unfixed dye is eluted out as a coloured effluent in the hydrolysed form. The addition of salt and alkali depends on the depth of the shade to be produced (Agarwal and Bhattacharya, 2010;Chattopadhyay, Chavan, & Sharma, 2007;Chinta and Vijaykumar, 2013;Kanana et al, 2006;Lewis and Mcllroy, 1997a,b;Montazer, Malek, & Rahimi, 2007;Teng, Ma, & Zhang, 2010).…”