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Foam dyeing process cuts water and chemicals in denim production

By Scott Jenkins |

foam dyeing

Indigo Mill Designs

Foam dyeing, a new technology for dyeing cotton yarn that is being applied to denim production for the first time, eliminates the use of several chemicals and can reduce water use by up to 90% compared to traditional dyeing. The foam-dyeing process, known as IndigoZERO, was developed at the Fiber and Biopolymer Research Institute at Texas Tech University (Lubbock; www.texastech.edu) and is being commercialized by Indigo Mill Designs LLC (IMD; Greensboro, N.C.; www.indigomilldesigns.com).

Traditional dyeing of denim involves dye baths, in which the indigo dye is treated with a reducing agent (sodium hydrosulfite) and pH-adjusting sodium hydroxide to render it soluble in water. The cotton yarns used for making denim are dipped continuously as ropes into the baths, and then removed and exposed to air in a step called skying to oxidize the indigo back into its raw form to color the yarn. Making denim typically requires six or more dip-and-skye cycles and several rinses, all of which require substantial amounts water, which then must be treated.

The foam-dyeing process, on the other hand, uses surfactants to generate an aqueous dye-containing foam, which is then pushed into intimate contact with cotton yarn in an oxygen-free chamber. The dye is converted back to indigo in a subsequent oxidation chamber to dye the cotton blue. The Texas Tech/IMD process has allowed foam dyeing to be used to color yarn with indigo, opening its use in denim production. Previously it could only be used on already woven fabric.

The new process has a host of environmental benefits without adding cost. Traditional denim production requires 400 gal of water for each 100 yards of fabric, also with 370 lb of NaOH and 39 lb of reducing agent for 100 lb of raw indigo dye, explains Sudhakar Puvvada, an advisor to IMD and the leader of the denim global innovation center for Wrangler and Lee brands, which have invested in the technology. Foam-dyeing eliminates the need for NaOH and sodium hydrosulfite, and reduces the water requirements to 3.5 gal per 100 yards of fabric, he says. Electricity consumption and physical footprint of the dyeing operation are both reduced substantially as well, Puvvada adds.

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