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These new textile dyeing methods could make fashion more sustainable

These new textile dyeing methods could make fashion more sustainable2018.08.29

In early June, Dalton Cheng realized something big was afoot. Cheng, who is head of technology for the textile printing firm Intech Digital, heard from customers that Chinese government authorities in Jiangsu province had shut down massive factories that produce synthetic dyes used by the textile industry.

It was just the latest in a series of actions that started in the summer of 2017, when tens of thousands of China’s factories were forced to close and undergo environmental inspections.

Overall, as much as 60% of China’s denim-dyeing chemical capacity has been shuttered, Cheng says, equal to roughly 30% of global capacity. And that’s why his phone was ringing. Intech, headquartered in Hong Kong, might be in a position to help apparel industry customers out of a critical supply bind.

Intech’s specialty is digital printing on textiles, including cotton and other cellulosic fabrics like rayon. Printing textiles with pigments rather than dyes uses very little water, Cheng says, and produces much less waste than traditional methods.

Digital printing is one example from a growing list of new, more sustainable fabric-coloring technologies from both major suppliers and smaller chemical and biotech start-ups. The companies see business opportunity in tackling dyeing’s wasteful water and energy practices and its reliance on toxic chemicals that can give rivers shocking hues and harm human health.

But the barriers facing those working to promote a more sustainable textile technology are quite high. The industry’s sheer scale makes it hard to have an impact: Textiles are a $3 trillion-per-year business that employs nearly 60 million workers worldwide, according to economic research firm Euler Hermes and FashionUnited, an industry information resource.

It’s also a manufacturing industry under pressure. Price competition is fierce, and profits are shrinking thanks to volatile raw material costs and rising wages. Despite public commitments by apparel brands to become more sustainable, suppliers contacted by C&EN say their customers will not buy anything that could raise the cost of a finished garment by as little as a penny.

The factory shutdowns have disrupted the textile supply chain, says Holger Schlaefke, global marketing manager at Huntsman’s textile effects segment. Huntsman, Archroma, and DyStar are the world’s largest suppliers of dyes and textile chemicals.

Shutdowns are a concern for companies like Huntsman and also for retailers,” Schlaefke says. “You can imagine retailers have contracted with a fabric-producing mill—they negotiated six months ago and agreed on a price—but suddenly that price is not certain anymore. It’s not a crisis, but it makes business a little more complicated for everyone.”

The largest impact of the factory shutdowns has been in the supply and price of so-called disperse dyes, which are used to color synthetic fibers like polyester, a specialty of Chinese producers, Schlaefke says. Availability of reactive dyes, which are used on cotton, was also reduced, though manufacturers in cotton-rich India are likely to take up the slack.

In India as well, the government is taking steps to reel in the textile industry to save precious water resources. “In India, a trend is huge investment in wastewater treatment for liquid discharge,” Schlaefke says. It’s now common for factories to reuse 90% of their water.

While both cotton and polyester are normally colored with synthetic dyes, dyeing cotton is a more water- and heat-intensive process. The surface of cotton fibers is negatively charged and doesn’t readily react with negatively charged dye compounds.

Even with an assist from salts and alkali added to the dye solution, cotton takes up only about 75% of the dye. To ensure colorfastness, dyed fabric or yarn is washed over and over again in hot water, creating large amounts of wastewater.

All told, about 200 L of water is used to produce 1 kg of fabric. A review of wastewater treatment steps found that textile effluent contains high concentrations of dyes and chemicals, including chromium, arsenic, copper, and zinc. Dyes and chemicals released into waterways also block sunlight and increase biological oxygen demand.

To reduce this burden, Huntsman has developed a line of dyes for cotton called Avitera that bonds to the fiber more readily. According to the company, the colors require one-quarter to one-third less water and one-third less energy. Three reactive groups are attached to the dye formula’s chromophore—or color-providing molecule—compared with the one or two reactive groups common for cotton dyes. Thanks to these extra reactive groups, the dye step lasts about four hours, compared with seven hours for conventional dyes.

Still, it takes a lot of legwork to sell customers on a new suite of dyes. “It can be hard to show cost savings when the savings comes from water use or energy,” Schlaefke says. Different regions and countries have different cost structures, he says. For example, Bangladesh is now the biggest cotton-producing country, “and as we know, they have no shortage of water,” he notes.

Another way to improve the bond between dyes and cotton fibers is a process called cationization. In North Carolina, textile industry veteran Tony Leonard is taking that approach. Leonard is the inventor and technical director behind ColorZen, a start-up that has developed a cotton pretreatment step.




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