A comprehensive review of the advances in process engineering and greener solvents in dyeing to impart sustainable textile manufacturing

The textile dyeing industry is not only seen as one of the largest environmental polluters, but dyeing operations also have high carbon footprints. Considering the current global water and energy crisis and to address the UN's sustainable development goals, it is of utmost necessity to make textile materials and their manufacturing sustainable. Over the years, improvements in machinery design, process engineering, and the development of green solvents have been made to reduce energy, water, and chemical usage as well as the environmental impacts of dyeing. Despite their potential, significant challenges remain in developing a dyeing method that is zero-effluent, economical, industrially feasible, and eco-friendly. This review article critically discusses various aqueous and waterless sustainable dyeing methods investigated, along with their dyeing mechanisms, recyclability, merits, and demerits. The dyeing performance and colourfastness properties of the fabrics dyed by various sustainable dyeing methods have been compiled and compared. Supercritical carbon dioxide (scCO2) and decamethylcyclopentasiloxane (D5) have emerged as the two most promising green alternative dyeing media. The ionic liquid, reverse-micellar, and D5-based dyeing methods are virtually zero-effluent but are not industrially feasible due to various issues, including industrial dyeing machines are not designed for solvent dyeing, requiring the handling and use of a large amounts of harmful solvents, and the difficulty of the removal of some solvents from the dyed fabrics. Conversely, scCO2-based dyeing is primarily suitable for dyeing polyester fibres with disperse dyes but is unsuitable for dyeing cotton, wool and other fibres as the dyes used in their dyeing are not soluble in scCO2 medium. The findings of this review will aid in the development of future industrially feasible, sustainable dyeing methods that are zero-effluent, economical, and eco-friendly.