Case Study

DyStar Cleans Up Indigo

People have harvested plants from the Indigofera family for their rich blue pigment for thousands of years. But today, natural indigo has been supplanted by synthetic dyes reliant on aromatic solvents and heavy metals. To revamp its denim, Lindex turned to the chemical manufacturer DyStar, whose Indigo Vat 40% Solution is arguably the cleanest indigo dye on the market.

When Lindex sought to create a better blue jean in 2014, the Swedish retailer had its work cut out for it. Denim can be a noxious business, one that is as resource intensive as it is environmentally damaging.

Chief among the changes Lindex made to its jeans was its choice of dye. Although people have been harvesting plants from the Indigofera family for their rich blue pigment for thousands of years, natural indigo had long been supplanted by synthetic versions that can be reproduced more efficiently and reliably on a mass-produced scale.  

But industrial dyes bring with them a slew of aromatic solvents and heavy metals. You only have to observe the unnatural colors swirling in the polluted waterways of the Yamuna River in India or the Pearl River Delta in China to grasp their impact.

To revamp its denim, Lindex turned to the chemical manufacturer DyStar, whose Indigo Vat 40% Solution is arguably the cleanest indigo dye on the market. The dye has a Gold level Material Health Certificate from the Cradle to Cradle Products Innovation Institute, meaning that it contains no substance at a concentration of 100 parts per million or above that poses a risk to humans or the environment during its use.

Earning a Gold level Material Health Certificate for Indigo Vat 40% Solution is a massive achievement for DyStar because it means that there are no carcinogens, mutagens or reproductive toxins—everything’s been assessed.

Annie Gullingsrud, director of Fashion Positive

"Earning a Gold level Material Health Certificate for Indigo Vat 40% Solution is a massive achievement for DyStar because it means that there are no carcinogens, mutagens or reproductive toxins—everything’s been assessed,” said Annie Gullingsrud, director of the Institute’s Fashion Positive initiative “With Gold level Material Health Certificate, there's full transparency about chemical input.”

DyStar’s dye is unique among indigo colorants because it takes the form of a liquid rather than a powder, which can produce airborne particles that enter the lungs. The dyeing process occurs in closed system, further minimizing contact between workers and the agent.

“It is the fact that it's a liquid product that enables you to basically handle it very easily, so there's no manual weighing of a powder,” said John Easton, global ecology services manager at DyStar.

Besides using less water and energy than its conventional counterparts, the Indigo Vat 40% Solution also shows better color fixation, requiring fewer chemicals such as sodium hydrosulphite, a reducing agent that creates salt byproducts like sulphites and sulphates. By using 60 to 70 percent less sodium hydrosulphite, DyStar’s pre-reduced indigo produces a cleaner effluent that is mostly water.

Tinkering with dyes to make them safer to be around can be a bumpy process. “The technical components of a product depend on its chemical structure, just the way a drug depends on its chemical structure for effectiveness,” Easton said. “You can't just go back and start taking chemical elements out because you'll change the color, you'll change the performance, and [the dye] might not be any good anymore.”

Indigo, however, proved amenable to modification. “It was fortuitous that indigo is a very simple molecule,” Easton said. “Synthetic indigo's been around for a hundred years, but it's still the same chemical structure that's available from the plant. It's a fairly benign chemical structure, so that one wasn't too much of a problem in terms of getting it approvable.”

The Cradle to Cradle Products Innovation Institute isn’t the only group to give DyStar's indigo its seal of approval; the dye has also been greenlit by the Global Organic Textile Standard (GOTS), bluesign®, and Zero Discharge of Hazardous Chemicals.

Today, Lindex uses the pigment in almost 90 percent of its denim. Eventually, the retailer hopes to achieve 100 percent, according to Anna-Karin Dahlberg, production sustainability manager at Lindex.

“We are all the time seeking  better options for the production of our garments and this was one of the steps taken in our work towards offering a more sustainable range of fashionable garments,” Dahlberg said. “We identified DyStar’s liquid indigo dye to be one of the best choices for our denim.”

DyStar’s work with the dye isn’t finished. The company is currently conducting trials with an organic reducing agent  that will allow for the radical reduction of sodium hydrosulphite, according to Guenther Widler, head of technology, denim and sodamide, at DyStar.

"This will lead to salt-free dyeings with much clearer and cleaner wastewater, " Widler said.  

Cradle to Cradle Certification

The Cradle to Cradle Certification process guides designers and manufacturers through a continual improvement process that looks at a product through five quality categories—material health, material reutilization, renewable energy and carbon management, water stewardship and social fairness. A product receives an achievement level in each category—Basic, Bronze, Silver, Gold, or Platinum—with the lowest achievement level representing the product’s overall mark. 

Optimization Results for DyStar’s Indigo Vat 40% Solution

Material Health
Challenge: Synthetic dyes often involve a raft of toxic chemicals, including aromatic solvents and heavy metals.
Optimization: DyStar modified the indigo molecule so that it contains no substance at a concentration of 100 parts per million or above that poses a risk to humans or the environment during its use.
Material Reutilization
Challenge: DyStar has has earned a Gold level Material Health Certificate for Indigo Vat 40% Solution but not full certification.
Optimization: Achieving full certification is a possible next step.
Water Stewardship
Challenge: DyStar has has earned a Gold level Material Health Certificate for Indigo Vat 40% Solution but not full certification however, there is a noteworthy correlation between improved material health and water stewardship. Indigo powder needs to be reduced by a chemical such as sodium hydrosulphite, which creates salt byproducts like sulphites and sulphates.
Optimization: DyStar focused on improving chemistry to meet the criteria for a GOLD-Level Material Health Certificate. The company did ensure that water quality and quantity was addressed as they were developing the dye. DyStar’s pre-reduced Indigo Vat 40% Solution is a liquid that requires 60 to 70 percent less sodium hydrosulphite. Wastewater parameters, like chemical oxygen demand, sulfates and total suspended solids, are also drastically reduced. The result is a cleaner effluent that is mostly water. Achieving full certification is a possible next step.
Renewable Energy
Challenge: DyStar has has earned a Gold level Material Health Certificate for Indigo Vat 40% Solution but not full certification.
Optimization: Achieving full certification is a possible next step.
Social Fairness
Challenge: DyStar has has earned a Gold level Material Health Certificate for Indigo Vat 40% Solution but not full certification.
Optimization: Achieving full certification is a possible next step.