Reactive dyeing of flax fabric using supercritical carbon dioxide with organic bases

The dyeing feasibility of flax fabric was investigated with organic bases utilizing a pyrimidine-base reactive dye in supercritical carbon dioxide (Sc-CO 2 ). Effects of organic base, pickup rate, temperature, pressure, time, and concentration of organic base on the color strength (K/S) and fixation rates of the flax fabric were investigated. The results illustrated that successful dyeing was achieved due to the nucleophilic substitution reaction of difluoro monochloro pyrimidine group in Reactive Dark Blue KM-GR and hydroxyl functional groups in flax. K/S values of the dyed flax samples were enhanced when the dyeing parameters changed. An optimized dyeing procedure of flax fabrics was suggested with a pickup of 100 %, a temperature of 90 ℃, a pressure of 18 MPa, a time of 90 min, and an organic base concentration of 10 g/L in Sc-CO 2 . Additionally, the colorfastness of the dyed samples, including rubbing, washing, and light valued over 5 was presented. In general, this work combines the synergistic advantages of fabric pre-treatment and Sc-CO 2 dyeing to explore a green dyeing process with low water consumption and high dye uptake. • Pioneering application: First successful demonstration of supercritical carbon dioxide (Sc-CO₂) dyeing of flax fabric using the reactive dye Reactive Dark Blue KM-GR, expanding the scope of this eco-friendly technology beyond synthetic fibers. • Mechanistic insight: Identification of triethanolamine (TEOA) as the optimal organic base, crucially catalyzing the nucleophilic substitution reaction between the dye's difluoro monochloropyrimidine group and the flax fiber's hydroxyl groups within the Sc-CO₂ medium, leading to significantly enhanced color strength (K/S) and fixation rate. • Comprehensive process optimization: Systematic investigation and establishment of optimal dyeing parameters (100 % pickup, 90 °C, 20 MPa, 60 min, 10 g/L TEOA) for achieving high dye uptake and fixation on flax in Sc-CO₂. • Superior product quality: Sc-CO₂ dyed flax fabric exhibits excellent levelness, good color fastness, and maintained mechanical properties, demonstrating the process's capability to produce high-quality dyed textiles. • Sustainable solution: Validation of Sc-CO₂ as a viable, water-free, and eco-friendly alternative to conventional aqueous dyeing for flax, offering significant environmental benefits through pollution reduction.