Comprehensive study on cellulose swelling for completely recyclable nonaqueous reactive dyeing

The swelling of cotton by non-nucleophilic organic solvents was investigated to achieve completely recyclable reactive dyeing. The degree of swelling was determined and correlated to the Hansen Solubility Parameter distance (Ra) of cellulose to the solvents and the dielectric constant of the solvents (ε). The effect of swelling temperature was also investigated. Preswelling of cotton fabrics by 150 °C N,N-dimethylacetamide (DMAc) for 1 h was found to be sufficient to accelerate dye sorption. Dyeing was carried out using C.I. Reactive Red 24 in a 40/60 mixture of DMAc and dimethylcarbonate (DMC), a cosolvent selected to facilitate dye exhaustion. The efficiency of unfixed dye removal was found to predominantly correlate to swelling (R² = 0.9236). Excellent colorfastness was achieved with 4 rinses by 95 °C DMAc. A 10-cycle repeated dyeing sequence was demonstrated to give 43% and 90% reduction in dye consumption and disposal. The overall reduction in material disposal was estimated to be over 99.99%. The favorable results indicated that discharge-free reactive dyeing could be made possible.