Supercritical fluid dyeing technology

Supercritical fluid refers to the phase of a substance with both temperature and pressure higher than the critical point (the point where liquid and gaseous phases of a substance become indistinguishable). This phase of a substance enjoys many advantages and can replace water in the dyeing process. The supercritical fluid normally used is carbon dioxide (CO ), as the critical temperature and pressure are easier to achieve than that of other substances. 

A Duteh eompany has imveiled what it believes to be the first commercial dyeing maehine to replaee water with supercritical carbon dioxide - a pressurized form of the gas with unusual liquid-like properties. Heated up to 31°Celsius (88 degrees Fahrenheit) and pressurized to 74 bar, CO takes on the characteristics of both a liquid and a gas, allowing for the dissolution of eompounds such as dyes. For DyeCoo Textile System s purposes, scCO is heated to 120°Celsius (248 degrees Fahrenheit) and pressurized to 250 bar. Behaving as both a solvent and a solute, the superehaiged earbon dioxide penetrates textile fibres and disperses the preloaded dyes without extra ehemical agents. 

Once the dyeing cycle is complete, the CO is gasified to recover the excess dye. Unburdened, the clean CO cycles back into the dyeing vessel for reuse, a manoeuvre that saves energy, water, and the heavy metals that comprise much of the toxic runoff into our planet s polluted waterways, according to DyeCoo. The process isn t without its limitations, however. DyeCoo is currently only able to dye scoured (or prewashed) polyester fabric, although the company notes that it s working on a version that will dye unscoured fabric, as well as reactive dyes for cellulosie textiles made from plants. 

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Bach, E., Cleve, E., and Schollmeyer (2002). Past, present and future of supercritical fluid dyeing technology— An overview,... 

Supercritical fluid CO / supercritical fluid dyeing technology... 

In the area of preparation and dyeing, there are waterless processes based on supercritical carbon dioxide fluid (SCF) technology. These use no water at all, and drying is simply a matter of allowing the carbon dioxide to evaporate, which happens immediately upon releasing the supercritical pressure. Since there is no water or pollution associated with the process and the CO2 evaporates without any applied heat, energy is saved [5]. Intensive research is underway to commercialize this process. 

Instead of current aqueous dyeing systems, DiyDye fabrics will be dyed using supercritical carbon dioxide in a stainless steel chamber developed and tested by DyeCoo. Yeh Group says, for the past three decades, supercritical fluids have been used in various extraction processes, including the extraction of natural substances for the production of pharmaceuticals, cosmetics and spices. In addition, leading producers of textiles dyestuffs have attempted to harness the technology for textiles dyeing but none has produced a successful commereial system to date. 

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