Sustainable Chemistry Method to Improve the Wash-off Process of Reactive Dyes on Cotton

Abstract

Reactive dyes are extensively used for coloration of cellulosic fibers because of their excellent wash fastness (stability to washing with aqueous detergent solutions), which arises from covalent bond formation between dye and fibre. However, up to 40% of the dyestuff may hydrolyze in the dyeing process; this hydrolyzed dye has affinity for the fibre via hydrogen bonding and van der Waals interactions, but is not covalently bonded and as such exhibits poor wash fastness. Accordingly, these reactive dyeings require a multi-step 'wash-off' process after dyeing, 2 involving various aqueous rinses and washings, in order for the dyeing to achieve the characteristic very high wash fastness. Wash-off and subsequent effluent treatment can account for up to 50% of the total cost of reactive dyeing and consumes significant amounts of water and energy; from a sustainable chemistry and engineering perspective, consumption of water and energy are arguably the biggest issues in textile dyeing. Existing and developmental dye transfer inhibiting (DTI) polymers were employed to remove unfixed (hydrolyzed) dyes. It was found that the use of DTI in the wash-off of reactive dyes enables a much more efficient, economical and sustainable process to be developed, which significantly reduces operation time, water consumption and energy consumption. Different DTI polymer types varied in their efficacy of dye removal; poly(vinylpyridine-N-oxide) polymers were the most effective with respect to the level of hydrolyzed dye removal closely followed by the poly(vinylpyridine betaine) polymers, which were also highly efficient in hydrolyzed dye removal, with poly(vinylpyrrolidone) polymers being the least effective. These differences were attributed to variations in the magnitude and delocalization of positive electrostatic potential of the functional moieties in the polymers and the extent of and propensity for hydrogen bonding with the hydrolyzed reactive dyes. IntroductionCotton and other cellulose substrates comprise over 40% of world textile consumption. Of all the dyes employed for coloration of cellulosic fibers, reactive dyes find greatest use with over 50% of world consumption. [1][2][3] Reactive dyes are desirable because of their excellent wash fastness, which arises from covalent bond formation between dye and fibre through either 3 nucleophilic substitution or Michael addition reactions, depending upon the nature of the reactive group in the dye. Reactive dyeing essentially has two stages. In the first stage, the dye adsorbs onto the cellulosic substrate through hydrogen bonding and van der Waals interactions; dyes are applied from aqueous solutions with electrolyte (sodium sulfate or sodium chloride), 4 which is needed to overcome the long-range repulsion forces operating between anionic dyes (as a result of water-solubilizing sulfonic acid groups) and the negative zeta potential acquired by cotton surface in aqueous media. 5 Moreover, this repulsive force can be exacerbated through the formation of anionic carboxylic acid (COOH...

Improved garment longevity and reduced microfibre release are important sustainability benefits of laundering in colder and quicker washing machine cycles

“…While it is known that dye transfer occurs, and indeed which dyes exhibit poor wash fastness, the identification of dyes that bleed in modern consumer textiles is little understood. The use of dye transfer inhibitors (DTIs) in domestic laundering detergent compositions is well-known; cationic and zwitterionic surfactants in formulations containing non-ionic and/or anionic surfactants hold soils and vagrant dye, which may be washed from fabric during laundering, in solution and prevent their redeposition onto fabric [18,19]. Current DTIs still work on the assumption that direct dyes are the most problematic dye species and so have often only targeted them [20];…”

“…however, most cellulosic fibres are now dyed with reactive dyes, and hydrolysed, unfixed reactive dyes pose a highly significant issue in terms of desorption and staining. Hydrolysed reactive dyes typically have significantly different geometries in comparison with direct dyes and their interactions with current DTIs are limited; in comparison planar, often larger, direct dyes have a greater extent of interaction with existing DTIs [19]. In previous research, technical fabrics are used or dyebaths are simulated, using known dye standards, but even applying optimal parameters for dye removal to real-life textile effluent yields discrepancies due to the difference between authentic textile effluent and synthetic dye solutions [21][22][23][24].…”

Sustainable washing‐free printing of disperse dyes on polyester fabrics enabled by crosslinked fluorosilicone modified polyacrylate binders

“…Disperse dyes are mainly used in the dyeing and printing processes (DPPs) of PET fabrics due to their low solubility, small molecule, and good fastness 17‐21 . Nevertheless, washing process, such as reduction clearing, is necessary to be performed to remove surplus disperse dyes and residual chemical auxiliaries after the traditional DPPs 15,22,23 . Unfortunately, washing process not only consumes a mass of water resource, but also produces and discharges a large amount of wastewater 24‐29 .…”

Removal of Reactive Dyes in Textile Effluents by Catalytic Ozonation Pursuing on-Site Effluent Recycling

“…Some studies have focused on reduction of water consumption in the textile wash-off process. Special chemicals have been developed to improve rinsing efficiency, such as dosing functional polymers that can inhibit dye transfer [21] or adding micro-absorbents [22] in rinsing baths to remove residual dyes. These technologies mainly focus on reducing dye concentration in the rinsing bath to improve its cleaning capacity and reducing the number of rinsing baths to save water.…”