Nanocellulose-Based Sustainable Dyeing of Cotton Textiles with Minimized Water Pollution

This research aims at minimizing environmental pollution by effluents discharged from current textile dyeing processes. The reduction of pollution is approached with a nanofibrillated cellulose (NFC) dyeing method. In the commonly used exhaust reactive dye bath cotton dyeing process, water effluents are contaminated with unreacted dyes and dyeing formulation auxiliaries amid the consumption of 20 weight units of water per weight unit of colored textile products. It was recently demonstrated that using reactive dye-colored NFC hydrogels-an aqueous dispersion of the NFC pigment-a sustainable dye carrier-results in 6-fold reduction in consumption of water and auxiliaries. Here, we report further developments of this technology. Cotton fabrics and NFC hydrogels inherit a fraction of soluble polysugars that react and conjugate with the reactive dyes. These soluble dye-conjugated polysugars are released into the wastewater, thus resulting in water pollution and also in reduced efficiency of the dyeing process. We demonstrate here that post-treatment of NFC-colored cotton textiles with polycarboxylic acid secures permanent chemical grafting of the soluble dye-labeled polysugars and forms chemical cross-links with the NFC fibers on the cotton fabric via the esterification reaction. This combination leads to the improvement of dye fixation by 30% and reduces the dye discharge in the washing stage by 60%. This enhancement is approached without compromising the stiffness and breathability of the fabrics. The advanced textile method is tested for a series of reactive dyes covering the entire visual spectrum range.