Dyeing,  News

Potential of DyStar’s Sodium Hydrosulfite-Free Indigo

There is a small revolution coming.

Although the news of DyStar launching a new, sodium hydrosulfite-free indigo dye, which the chemical company introduced to the public late last year, went almost undetected by the fashion media, its potential for the industry cannot be stressed enough.
Here’s why: Indigo is not a conventional dye. It is insoluble in water and must first undergo a chemical reaction that will turn it into a soluble, dye-friendly form. This can be done with bacteria during a fermentation process, which is considered green but takes time and is therefore not popular with the mass market, or it can be achieved via a powerful reducing agent and hazardous chemical called sodium hydrosulfite, which has dominated the industrial process since synthetic indigo conquered the market.

Pre-Reduced Indigo
Until now, industrial indigo aficionados who were looking for a greener spin, had the possibility of using DyStar’s pre-reduced indigo formula, branded as Indigo Vat 40% Solution, which comes with improved safety for workers, considerable chemical savings and reduced sludge formation in the wastewater. Compared to an indigo powder process, the pre-reduced liquid formula saves 15% indigo, 70% sodium hydrosulfite and caustic soda, respectively. On a global scale, this translates into savings of 55,000 tons of hydrosulfite, 27,000 tons of caustic soda and 4,000 tons of indigo per year. Still, only about 40% of world’s denim is dyed this way.

New Formula
The new formula, which DyStar markets under the commercial name Sera Con C-RDA, does entirely without hydrosulfite. It’s a combination of Dystar’s pre-reduced solution and a new liquid organic agent that substitutes sodium hydrosulfite. It is biodegradable and yields no salts as a by-product, which are difficult to remove from the effluent and which make the recycling of indigo wastewater challenging. The agent also reduces the build-up of hazardous sulfates in the wastewater by 95 percent. Sulfates can release a harmful gas upon reaction with other chemicals present in oceans and rivers, harming aquatic life. Translated into figures, the new formula saves

  • 30,000 tons of salt waste in a year, equal to 1,200 truckloads that would otherwise end up in landfill;
  • up to 3.25 billion liters of water, which is equivalent to the needs for drinking water of 3.5 million people per year;
  • and other chemicals used in the process, such as caustic soda, which goes down by 70 percent. (The savings are calculated against the simple usage of pre-reduced indigo only.)

Where to find it ?
DyStar joined forces with Pakistani denim mill Artistic Milliners which brands the process as “Crystal Clear,” and G-Star, which has incorporated the new dyeing process into its “most sustainable jeans” yet for spring 2018.

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