Review on Dyeing of Natural Fibers in an Environmentally Friendly Solvent

Supercritical fluids have found numerous promising applications due to its excellent properties. A number of research groups have also investigated the application of scCO2 to textile dyeing. Dyeing in supercritical fluids has been identified as a new and acceptable method that has been replaced with conventional dyeing methods of not discharging waste aqueous effluent containing colored compounds and concentrated electrolytes. Today, there is a need to reduce the amount of wastewater containing dye, chemical agents, and the like in the conventional method for the dyeing of textiles from the viewpoints of the cost of wastewater treatment and environmental pollution. In this way, a new dyeing method using supercritical CO2 fluid, supercritical fluid dyeing, has been developed. Dyeing in supercritical CO2 is carried out analogous to aqueous systems. Both decisive tasks of water at dyeing, which means the transport of dyestuff and heat to the fibre, are in the new dyeing process replaced with supercritical fluids. The new dyeing method is particularly attractive as it is non-toxic, non-flammable, and cheap. In addition CO2 has mild critical conditions and can easily be recovered and recycled after use. The aim of this paper is to provide the reader with an up-to-date overview of this subject. Wool and silk fibers have found several applications in textile industry especially in hand-knotted carpets. In this paper, various methods for the dyeing of these fibers in supercritical CO2 has been investigated, which is, at the moment, the limiting step of this technology.