Blue planet, green ideas | Blue jeans plus green

Can we reduce the environmental impact of the famous blue jeans? This is the bet of Danish chemists. Their solution: indican, an enzyme that is a precursor to indigo, the dye that gives denim its characteristic look.

Indigo used for dyeing denim, a cotton fabric invented in France in the 16th century^e century, was initially taken from the indigo tree, a plant. “But for half a century, we have been using synthetic indigo, a very toxic chemical,” explains Katrine Qvortrup of the Technical University of Denmark, who is the lead author of the study published at the end of February in the magazine Nature Communications. “It is insoluble, which requires the use of solvents to use it as a dye. This explains the toxicity of denim dyeing effluent. »

The synthetic indican invented by M^me Qvortrup takes advantage of “photochemistry”, or chemical transformations linked to light, to reduce the toxicity of water discharge from the dyeing process. “We believe that photochemistry is one of the most promising avenues for achieving a green chemical industry. »

The indican synthesized by Danish researchers generates a type of indigo that requires fewer chemicals to give denim its characteristic blue. According to their calculations, it would be 3000 times less damaging to the environment than current products, in particular thanks to a reduction in greenhouse gas (GHG) emissions of 3.5 megatons per year. According to Greenpeace, the clothing industry generates between 4,000 and 5,000 megatons of GHG emissions per year.

The indican synthesized by M^me Qvortrup is also more stable than synthetic indigo.

“There is therefore no effluent, no use of water, in this second stage. We also verified that LED lamps can be used to reduce energy consumption in this second stage. »

Montreal jeans

At Yoga Jeans, a Montreal jeans manufacturer, CEO Eric Wazana indicates that the indican is the talk of the industry. “I heard about it at a meeting with my chemists,” says Mr. Wazana. What people love about indigo is that it slowly becomes less dark with each wash. It gives different shades of blue. Pale blue is currently in fashion. We can accelerate the fading with bleach, but we don’t do it out of respect for the environment. Otherwise, there are enzymes that accelerate fading. The indican allows you to start with a less dark blue. Purists will notice the difference, but for the average consumer, it works. »

This kind of research is important for the fashion industry. “We are constantly pushing to be more environmentally friendly [environment friendly], said Mr. Wazana. For example, we take American cotton because that’s where environmental rules are more respected, because inspection is strict. » American cotton from Yoga Jeans is sometimes sent to fabric manufacturers elsewhere in the world, including Mexico and Brazil. Cotton dyeing is done by the fabric manufacturer.

Question of economic feasibility

M’s team^me Qvortrup was keen to make economic feasibility calculations for this new technology. “We collaborate with industry, because innovation that is not adopted is of no use. We also have three possible avenues for applying the technology, with different enzymes and at different times during fabric manufacturing. We also took into account investments in equipment and workforce training. Currently, denim dyeing is mainly done in poor or emerging countries, the vast majority in Asia. We don’t want these countries to lose jobs because greener denim dyeing technology is only available to rich countries. »

The cost of manufacturing synthetic indican would be US$12 per kilo, compared to US$5 per kilo for current synthetic indigo, which would add a bill of US$35 million to the industry, or less than 0. 1% of total sales.

Danish researchers are not the only ones looking into the issue. In 2022, the Californian firm Huue has raised US$15 million in venture capital for a pilot plant for its organic indigo technology.

M^me Qvortrup normally studies anti-cancer drugs and medical biomaterials. How did she become interested in jeans? “I lived in the United States during my studies. It’s the home of jeans. I always wondered what its environmental footprint was. »