Danish scientists develop a sustainable alternative to ‘Indigo Dye’

For centuries, indigo has been the dye of choice for creating denim’s iconic blue color. Indigo is the sole molecule that produces the distinctive hue that blue jeans are known for. In a billion-dollar industry like blue denim, the overwhelming demand has made synthetic indigo the standard for blue jeans production. 

The traditional dyeing process carries a significant environmental burden. Synthetic indigo, being insoluble in water, necessitates a chemical reduction process, typically involving sodium dithionite, to bind to fabric. This process can release harmful substances into waterways, contributing to pollution and posing risks to human health.

The denim industry consumes approximately 50,000 tons of synthetic indigo annually and around 84,000 tons of the reducing agent, sodium dithionite, as reported by the American Chemical Society. The adverse environmental and social impacts of synthetic indigo production include water and soil pollution, which could result in crop damage and human toxicity, according to the study.

Figure: Untreated or partially treated effluent from textile factories, usually blue / indigo in color, is killing African rivers, Flags Report. Photo: Water Witness

The Danish Solution: Indican-Based Dyeing

Researchers from the Technical University of Denmark have introduced an innovative technique for dyeing blue denim that reduces environmental impacts associated with indigo by an impressive 92%. By utilizing indican, a natural precursor that is soluble, instead of traditional indigo, the need for treatment with potentially harmful chemicals like sodium dithionite is eliminated.

Indigo creates this really fantastic hue that we all know and love, but we are producing it from petrochemicals because the demand is simply too high. Synthetic indigo is not a “dyeing competent” on its own, so reducing chemicals are needed to treat the denim, which leads to some environmental challenges in the dyeing hubs of the world.

Ditte Hededam Welner, lead researcher of the study and biologist at the Novo Nordisk Foundation Center for Biosustainability in Denmark

Indican, a precursor to indigo, is naturally found in the same plant species, Indigofera. “Indican, the β-O-glucoside of the indigo precursor indoxyl, is the natural storage form of indigo in indigo-producing plants,” according to the study. This compound has been proposed as an environmentally friendly alternative for dyeing blue denim, as indican dyeing eliminates the need for reducing agents while still resulting in the desired indigo color in the yarn.

One of the key advantages of indican is its water solubility, which allows for its application to denim without the use of harmful chemicals. The innovative dyeing process involves treating the denim with indican, which then transforms indigo through either a harmless enzymatic process or exposure to light. This method not only reduces the environmental impact of traditional dyeing processes but also produces high-quality, sustainable denim products.

The current challenge lies in the need to increase the production of indican in order to meet the demands of the global denim market. By scaling up the production of indican, it is possible to eliminate the use of toxic chemicals currently employed in denim dyeing, thus creating a much cleaner and more sustainable process.

The denim industry has the opportunity to lead the way in adopting this innovative approach. By investing in the establishment of indican production facilities and integrating this eco-friendly dye into their manufacturing processes, the industry can make a significant impact on reducing its environmental footprint.

As consumer demand for sustainable clothing continues to grow, indican offers a commercially viable solution for the denim industry. So, buyers should communicate very clearly that they’re interested in buying sustainable denim. Thus, they can put some pressure on the brands. This presents a win-win situation: the environment benefits from reduced pollution, while consumers can enjoy their favorite blue jeans knowing they are making a positive impact.

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