Indican over indigo
Textile dyeing is one of the world’s most chemically intensive industries, generating large amounts of intensely colored wastewater that contains a diverse range of persistent pollutants. An important contribution comes from the production and usage of indigo, the only known dye to give rise to the iconic blue denim look.
A team of researchers from DTU Electro and DTU Chemistry takes an innovative approach. Instead of doing what other players in the industry have done – looking for alternatives to indigo, to indigo reduction, or to indigo production – they focus on indican, nature’s own indigo precursor.
Indican is a promising dye precursor since it can be converted to indigo with mild treatment, resulting in the exact same chemical as what is currently used, i.e. aesthetics and functional properties of the dyed yarn are preserved.
The team builds on their novel and groundbreaking discovery: that textiles can be dyed with indican using only light. Their economic and environmental calculations show that these novel technologies have the potential to reduce dyeing impacts with an order of magnitude, while conferring an additional cost of a pair of jeans of less than 1€.
The specifics
The project will mature the indican-based light-driven denim dyeing technology and develop technologies for industrial operational light-driven denim dyeing, ending up in production of an indican-dyed yarn test sample in pilot scale. Specifically, they will:
- Optimize the dyeing process to be technically feasible and economically viable at industrial scale.
- Develop a scalable dyeing system with continuous in situ measuring of both indican concentration and indigo waste as well as yarn color.
The team aims to accelerate the commercialization of indican as a low-impact and economically
feasible indigo dye with the goal of enabling an economically competitive, environmentally mild, and socially acceptable blue denim dyeing globally.
The core of the scientific approach is an interdisciplinary effort involving photochemistry, optical
engineering and process engineering, tightly governed by a continuous and dynamic dialogue
between technical results and sustainability assessments.
By accelerating the commercialization of indican, Denmark will gain an edge in the global denim market which is projected to €87.4 billion by 2027.
Impact
The textile industry is a major contributor to global pollution, accounting for up to 20% of global water pollution and 10% of global carbon emissions.
A big player in the textile industry is the denim market. By accelerating the commercialization of indican, Denmark will gain an edge in the denim market which is projected to €87.4 billion by 2027.
In 2020, indigo accounts for 50-70% of all dyes used in the denim industry. Depending on the indigo production process and dyeing process, 5-25% of harmful chemicals end up in wastewater.
By eliminating 100% of the harmful chemicals and reducing the use of water and energy >50%, our low-impact process paves the way for elimination of pollution from blue denim dyeing, including the pollution stemming from upstream dye production as well as from the dyeing process itself. This would help to address some of the world’s most pressing societal challenges, such as climate change, CO2 emissions, and biodiversity loss. Additionally, our technology can promote greater health and welfare for workers in the denim industry, as they would no longer be exposed to dangerous chemicals.
In sum, the development of a low-impact process for blue denim dyeing will have significant
economic and societal impact. By reducing costs, boosting competitiveness, and addressing key societal challenges, our technology has the potential to transform the denim industry and pave the way for a more sustainable future. Supporting this game-changing innovation would make Danish textile manufacturers the pioneers of low-impact denim production, which will make a real difference in the world.
The consequences of indigo
Global indigo production is ~70 000 tonnes per annum, which is used to produce approximately four billion denim articles and the denim market is only expected to rise, making indigo one of the world’s most important industrial chemicals. Global annual market value of indigo is estimated to €1.2 billion in 2020 rising to €1.6 billion in 2028.
This large market has a significant environmental footprint, including 500,000 tonnes of CO2 equivalent emissions yearly, partly due to the chemical synthesis of indigo from petrochemicals, and partly to the alkaline and reducing conditions required for indigo vat dyeing.
Synthesis of indigo involves the hazardous chemicals formaldehyde, hydrogen cyanide, and sodamide, and is reliant on aniline, a toxic compound derived from benzene; residues of aniline and N-methylaniline remain trapped in the indigo granules and are released during dyeing.
The vat dyeing process also consumes large amounts of harsh chemicals generating corrosive and toxic wastewater, presenting a significant leakage risk.
Pollution of rivers and agricultural land surrounding the world’s dyeing hubs is a threat to biodiversity, water resources, and the livelihood of locals.
Several research efforts and innovations aim to replace the indigo dye and the dyeing process with ecologically attractive alternatives, but the economic and social aspects of sustainability are often overlooked, resulting in poor implementation.
The team has shown that indican can be produced at a raw materials price of max 12 €/kg with at least a 50% reduction in environmental impact compared to conventional indigo production. Using their novel light-driven indican denim dyeing method, the hypothesis is:
Indican can photolytically dye denim without an increase in process costs, and with at least a 73% reduction in environmental impact and added economic savings by reduced need for wastewater treatment, compared to conventional indigo dyeing.
