Copyright © Françoise Herrmann
It takes about 30 liters of water to dye a single tee-shirt using traditional water-intensive dyeing methods. In response, Nike is pioneering the use of ColorDry a waterless dyeing process that relies on the use of Supercritical CO2. Thus, for the estimated 30 million tons of polyester that Nike dyes yearly, the process is now waterless, with better and more consistent coloring of garments! [NIKE 1]
Various Supercritical CO2-based industrial processes, using less water and energy, are disclosed in the European patent application EP2876203A1 titled Supercritical CO2. EP2876203A1 discloses that SuperCritical CO2 is a fluid solvent technology widely used since 2011 by Nike, Adidas, and Ikea for coloring textiles . EP2876203A1 further recites that Supercritical CO2 is also a process widely used since the 1980s for decaffeination of tea leaves and coffee beans, and for extracting natural products in the pharmaceutical and cosmetics industries !
So, what is Supercritical CO2?
EP2876203A1 specifies that when a gas is sufficiently compressed, it becomes a liquid and that there is a critical temperature (Tc) and critical vapor pressure (Pc), when the gas is heated, beyond which the hot gas can never be compressed into a liquid. The substance just beyond Tc and Pc is a Supercritical fluid (SCF), that is, a substance that is neither a gas nor a liquid but that takes on many of the varying properties of both gas and liquid when the temperature and pressure are manipulated . The SCF CO2 then becomes solvent used for extraction or purification, or in the case of Nike garments, as a waterless dying process.
Wait a minute!... How can the use of Supercritical Fluid CO2 (SCF CO2) be beneficial to the environment if precisely the point is to reduce all the CO2 emissions that create the Greenhouse Gas effects (GHG)?
The process of dyeing garments using SCF CO2 actually recycles the SCF CO2 remaining in the dyeing vessel, as a gas, which is then liquefied anew and re-used. The following diagram shows the waterless SCF CO2 dyeing process, where the fabric is first rolled onto a perforated dyeing beam, which is inserted into a dyeing vessel. Inside the vessel, the SCF CO2 will be released, mixed with the dye, and forced through the fabric to color it. Then, the dye will be separated from the SCF CO2, and pressure lowered so that the SCF CO2 leaves as a gas, which is then compressed and liquefied for storage and re-used as SCF CO2. [NIKE 2]
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Going back to the patent application EP2876203A1 , it is further suggested that the sources of SCF CO2 could potentially be already sequestered liquefied CO2, so that SCF CO2 then becomes Carbon Capture and Use (CCU) technology rather than a controversial Carbon Capture and Storage (CCS) solution – at least until carbon capture still has to occur -- in the absence of a complete conversion to energy sources that no longer produce GHG emissions and CO2 in particular.
[NIKE 1] – Nike ColorDry
[NIKE 2] – Nike ColoDry process