Environmentally friendly salt-free and low-alkaline coloration of lyocell fibers in an ethanol–water mixture with excellent exhaustion

Abstract

The textile industry is a significant water consumer that generates wastewater containing salts, dyes, and various persistent chemicals, exacerbating the scarcity of freshwater resources. To address these challenges, the development of eco-friendly, sustainable, and recyclable dyeing methods is essential. Herein, we report an eco-friendly salt-free dyeing method (EHS) for dyeing lyocell fibers, which have gained attention for their excellent properties as a regenerated cellulose material. The synergy of adsorption, exhaustion, and fixation on the fiber was achieved in the EHS without using dyeing assistants. Lyocell fibers were swollen with sodium hydroxide, followed by dyeing in an ethanol–water mixture (9 : 1, v/v), achieving 99.54% dye exhaustion with a total fixation rate of 94.75%. The expansion medium could be reused 5 times, water consumption by the dyeing solution was reduced by 90.00%, and the dyeing solvent exhibited good recycling potential. The superior performance of the EHS over the conventional H₂O system was revealed through molecular dynamics simulations. Furthermore, the insightful adsorption and dyeing mechanisms between the dye molecules and the fiber were explained by binding interactions using electrostatic potential, molecular frontier orbitals, and Fukui indices. This sustainable approach aligns with green chemistry principles and offers significant improvements in water usage and waste reduction.