Non-aqueous Dyeing Of Cotton With Reactive Dyes In Organic Solvents And Its Environmental Impacts

As one of the most commonly used dyes in textile coloration, reactive dyes receives intensive attention from dyers and colorists, who have been devoted to improving fixation, reducing salt use and more effectively treating dyeing effluents. Nevertheless, unfixed and hydrolyzed dyes present in the dyeing effluent still represents the major environmental challenge associated with reactive dyeing. Swiching to inert dyeing media to suppress dye-hydrolysis and enable dyebath reuse denotes a potentially more effective and sustainable approach to the problem.This paper describes the development of non-aqueous reactive dyeing of cotton in mixtures of non-nucleophilic organic solvents. Specifically, solvent dyeing with vinyl sulfone(VS) dyes was investigated, intending to provide scientific basis for pilot-scale solvent dyeing of cotton yarn packages.Dimethyl Sulfoxide(DMSO) was selected to be used as both the swelling solvent and dyeing media for the non-aqueous dyeing process due to its superior ability to swell cotton and solvate VS dyes. As a co-solvent, Dimethyl carbonate(DMC) was chosen as an adsorption-promoting co-solvent to raise the chemical potential of VS dyes in the dye bath so that no salt would be needed. Both solvents are green solvents with excellent environmental health and safety profiles. It was found that dye fixation could not be realized without organic base was added in advance. 1,4-Diazabicyclo[2.2.2] octane(DABCO) was identified as the most effective base for promoting the reaction between vinyl sulfone dyes and cellulose. HPLC analysis revealed that the formation of an activated base-dye complex is crucial to facilitate the subsequent reaction with cotton cellulose. The spent liquor was confirmed to be free of hydrolyzed dyes and demonstrated for multiple reuse cycles with simple replenishment of dyes and chemicals and adjustment of the solvent ratio. The fabrics dyed from a 10-cycle reuse sequence displayed consistently good color depth and fastness. The method was found to be generally applicable to vinyl sulfone dyes with steadily good shade build-up and colorfastness. The new non-aqueous dyeing based on DMSO and DMC completely prevented reactive dyes from hydrolyzing, avoided using salt, and allowed for convenient reuse of dye baths. Therefore, it has great potential in sustainable development of the dyeing industry.The environmental impacts of reactive dyeing in traditional aqueous media and in mixed organic solvents were compared using a cradle-to-gate life cycle assessment(LCA). Specifically, large scale package dyeing of cotton yarns were compared using the CML-IA baseline method and the SimaPro software. A similar solvent dyeing process utilizing DMSO and perchloroethylene(PCE) was assessed instead of the DMSO/DMC process developed in our lab due to the absence of DMC in the SimaPro database. Life cycle inventory(LCI) of both dyeing processes were constructed based on real production data. The inventory mainly consisted of the consumption of chemicals and energy and the discharge of pollutant. Seven impact categories, GWP, AP, ADP, ADP(fossil fuels), ODP, EP and POCP, was considered in the assessment. It was found that the process of package dyeing in DMSO/PCE had no advantage in terms of environmental protection, with normalized value much higher than the aqueously dyed yarn. Contribution analysis and sensitivity analysis implied that the poor environmental performance of the DMSO/PCE process was associated with using PCE as the dyeing medium. The values could be effectively lowered if the release rate of PCE is cut down. The rather high dyeing temperature of 130 °C also contributed directly to high ADP values and indirectly to GWP and AP. The results of the LCA clearly point out ways to future improvement of the solvent-dyeing process toward a more sustainable end.