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Saving Water A Swimming Poolful At A Time

DyeCoo's CO2 polyester dyeing technology and ColorZen's cotton pretreatment technology drastically reduce water and chemical usage in textile wet processing.

Janet Bealer Rodie, Managing Editor

In the effort to raise the quality of life for all of the Earth's citizens — not to mention facilitating peaceful coexistence among the various populations — providing access to abundant, clean water is a paramount objective. The textile industry — particularly the dyeing and finishing sector — is one of the biggest industrial users of water, and much of the effluent from those operations is untreated, especially in unregulated operations in many developing areas of the world. Water usage statistics are mind-boggling: According to some estimates, 60 million metric tons of textiles are dyed each year at the rate of 100 liters of water per kilogram of material, which translates to some 6 trillion liters of water — equivalent to approximately 2.36 million Olympic-sized swimming poolfuls, or, put another way, equivalent to 219 days' supply of drinking water for the entire world population. In China alone, it is estimated that traditional textile dyeing generates 2.27 trillion liters of untreated wastewater each year.

Polyester materials comprise more than half of all textiles dyed, with 39 million metric tons projected to be dyed annually by 2015. Cotton textiles make up a large majority of the rest.

Sustainability
DyeCoo’s latest-generation dyeing machine features three dyeing chambers. The CO 2 recovery and supply unit serves all three progressively as dyeing steps are staggered from one chamber to the next.

Dyeing and finishing machinery manufacturers have developed technologies to reduce the amount of water needed to process fabrics, yarns and apparel. And textile dye/chemical manufacturers have developed technologies that considerably reduce the amount of salt and other chemicals needed in the dyeing process and offer improved dye uptake rates in the fibers, thus reducing the amount of chemicals discharged in wastewater as well as the amount of water needed for dyeing/finishing operations. Other new technologies aim to reduce still further or even eliminate altogether the amount of water needed for these processes and the impact of dyes and chemicals on effluent water quality. In this article, Textile World looks at two of these technologies — one for polyester dyeing and one for cotton dyeing.

DyeCoo®: Supercritical CO 2 Technology For Polyester
DyeCoo Textile Systems BV, the Netherlands, manufactures machinery that uses recycled supercritical carbon dioxide (CO 2) and modified disperse dyes to dye polyester fabrics. DyeCoo® technology uses no water, surfactants or auxiliary chemicals; and also uses less energy than conventional dyeing processes, potentially reducing operating costs by up to half.

The ability to use CO 2 instead of water in a textile dyeing process was discovered in the 1980s in Germany. In the 1990s, Geert Woerlee, Ph.D., formed FeyeCon Development & Implementation BV to investigate the technology's commercialization potential for dyeing as well as other processes. At first, Woerlee worked in cooperation with Delft University of Technology and Stork Prints. In 1999, he began to expand his company, and Ernst Siewers joined as partner and now serves as DyeCoo's chief technology officer. As R&D progressed, FeyeCon took over Stork's intellectual property related to the project, and in 2008, Woerlee brought in Reinier Mommaal, now DyeCoo's CEO, to obtain funding and establish DyeCoo as a spinoff devoted exclusively to bringing the CO 2 dyeing technology from pilot-scale to industrial-scale production.

SustainabilityB
Kenya’s 2012 Olympic marathon team wore uniforms made with CO 2 dyed fabrics and supplied by Nike.

In 2010, Thailand-based knit fabrics and garments maker Yeh Group, one of DyeCoo's backers, launched the production of DryDye™ fabrics dyed using the CO 2 process. This year, activewear brand adidas® introduced a DryDye T-shirt collection in select markets in Asia and Europe. The first run totaled 50,000 shirts — saving enough water to provide one day's drinking water for 750,000 people, or to fill approximately one Olympic-sized swimming pool — and adidas is expanding its distribution and offerings around the world and across product categories as quickly as production capacities, material and color scope allow.

Nike, also one of DyeCoo's backers, supplied uniforms made with CO 2 dyed fabrics to Kenya's 2012 Olympic marathon team and is interested in scaling the CO2 dyeing technology to apply across the industry, said Del Hudson, global communications director, sustainable business & innovation, Nike. "We believe it is the biggest innovation in textile dyeing in some time," she added.

The Process
The first-generation industrial-scale machine has one steel dye chamber connected to a CO 2 recovery and supply unit with pumps and heat exchangers. The fabric beam is placed in the chamber along with the dyestuff. Then, the chamber is pressurized and filled with CO 2. Heating CO 2 to a temperature above 88°F at a pressure greater than 74 bar makes it supercritical — a state at which it becomes fluid, allowing compounds to dissolve. In DyeCoo's dyeing process, CO 2 is heated to 216°F at 250 bar. As the supercritical CO 2 penetrates the polyester fibers, it causes them to swell so that the dyes it is carrying are diffused more easily, penetrating more deeply into the hydrophobic fibers and cutting dyeing time in half compared to traditional dyeing processes. The process enables all dyeing steps to be carried out in one batch.

As Siewers explained, the CO 2 contains a very small amount of dyestuff at the end of the process. It also extracts any moisture and spin oil that were in the fabric from the spinning and fabric-forming processes. The contaminated CO 2 is replaced with fresh CO 2 to "rinse" the chamber, which then is depressurized. When the contaminated CO 2 is no longer under pressure, the excess dyestuff, oil and moisture separate out of the solution, and almost all of the CO 2 can then be recycled to use in a subsequent dyeing operation.

DyeCoo now has developed a next-generation, more efficient machine that comprises three chambers. "In the first version, when the dyeing process starts, the other equipment is doing nothing. In order to utilize all parts in the best way, we can equip one machine with three dyeing chambers," Siewers said. "While the first chamber is dyeing, you can start filling the second, and then go on to the third. When the first chamber is finished, you empty the CO 2 back into the supply unit, and you completely utilize the supply unit also."

DyeCoo has partnered with Triade Chemicals, the Netherlands, to offer a full range of dyes to use with its process. It also has partnered with Huntsman Textile Effects, Singapore, to develop finishing products and fluorescent brighteners.

Siewers said that currently, conventional scoured fabric is dyed in the DyeCoo process, but the company is working on using its CO 2 technology for scouring as well. DyeCoo also is in early stages of developing the technology for use with cotton and other natural-fiber fabrics.

SustainabilityC

Activewear brand adidas® is offering DryDye™ T-shirts dyed using DyeCoo® supercritical CO 2 dyeing technnology, including this adidas for Stella McCartney DryDye T-shirt.

ColorZen™: Cotton Pretreatment Technology
ColorZen LLC, New York City, launched ColorZen™ technology for pretreating raw cotton fiber in August 2012. Company principals include President Michael Harari, who became involved in developing the technology in 2010; Technical Director Tony Leonard, a 30-year textile industry veteran with expertise in dyeing chemistry; and Director Eli Harari, a 32-year fashion and apparel industry veteran.

Having some basis in cationic chemistry, the ColorZen process alters the cotton fiber's molecular structure to make the fiber naturally receptive to dye uptake. Therefore, no salt is required, nor are other chemicals needed to fix the dye, and the desired color is achieved using half the amount of dye traditionally required, with consistent, uniformly level results and a 97-percent exhaustion rate. The pretreated cotton can be dyed in yarn, fabric or garment form using conventional equipment, but scouring and prebleaching steps are eliminated because many of the impurities in the raw cotton fiber are cleaned up during the ColorZen process, and far fewer rinses are required. Therefore, water savings of 90 percent and process time savings of 70 percent are realized, and energy savings amount to 75 percent. These percentage savings are realized whether using older, higher-liquor-ratio machines or state-of-the-art, low-liquor-ratio machines. In addition, because there is zero discharge of any chemicals in the process water, it could be recycled for a subsequent dyeing session, which would reduce water consumption even more.

The only dyeing auxiliary chemical used is a small amount of wetting agent, so overall chemical use is reduced by 95 percent. If the dyebath is recycled for reuse in a subsequent dyeing process, the wetting agent in the bath also can be reused.

According to Leonard, the process, while it costs a bit more than conventional cotton pretreatment processes, in the long run can provide cost savings, as no capital investment is required to buy new equipment; and the savings related to reduced energy, water and dye and chemical usage — not to mention the considerable time savings — combine to mitigate that initial extra cost.

The company has set up its first production facility in China, where many of the world's textile dyeing mills are located and many of the environmental issues surrounding textile manufacturing have arisen. ColorZen plans to expand its operations to other textile-producing countries as demand for its pretreated cotton grows.

To demonstrate the efficacy of the ColorZen technology, Leonard described a trial in which a Chinese customer dyed a dark burgundy shade first on conventional cotton using a conventional process and then on ColorZen cotton using the ColorZen process: "The conventional process took 10.9 hours and had more than 16 fill-drops, and then the effluent needed to be treated. With the ColorZen process, we were able to dye the same shade in 2.6 hours and only had two fill-drops, and one of those wasn't totally necessary — and no effluent treatment was needed."

SustainabilityD
T-shirts show dyeing possibilities, from solid colors on 100-percent ColorZen™ treated cotton to heathers on ColorZen/conventional cotton blends.

Flexible Downstream Options
Leonard noted that ColorZen treated cotton fiber can be spun together with conventional cotton to create a heather yarn when it is dyed using the ColorZen dyeing procedure. "The ColorZen fiber dyes and the other doesn't," he explained, noting the absence of the chemicals required to fix color on the conventional cotton fiber. "And, the yarn can be dyed either in fabric or garment form. It makes for some unique characteristics, as you can blend it in different percentages to create whatever look you want."

The treated cotton can be dyed using not only reactive dyeing — the most prevelant process for dyeing cotton because of the colorfastness achieved — but also certain other dyeing processes. "Direct dyes will dye ColorZen cotton very effectively and with better fastness than normal direct dyeing, and other dyes will have affinity to ColorZen cotton," Leonard explained. "We will be glad to work with any customer who wants to look at different dyes and techniques and see if the ColorZen procedure can be modified to give the required result."

ColorZen mainly is targeting the knit industry, but Leonard said the process can be applied for wovens or any 100-percent cotton fabrics. One possible exception is denim, which usually has an indigo-dyed warp.

"Indigo is a vat pigment. In reduced form, it has affinity for ColorZen cotton, but in oxidized form, it's a pigment, and true affinity is reduced," Leonard explained. "We've not recommended ColorZen for dyeing indigo, but you can make denim fabric using ColorZen cotton in the warp and dye colored denim, or dye a denim color using reactive dyes."

SusainabilityE
The beakers contain ending dye water from conventional cotton dyeing (left) and ColorZen cotton dyeing.

Conclusion
Currently, textile dyeing and finishing account for some 20 percent of untreated industrial wastewater worldwide, resulting in fish kills and other destruction in affected waterways and reducing the availability of clean water for human consumption and other needs. By drastically reducing water and chemical usage, the DyeCoo and ColorZen technologies can contribute to reversing that situation and ensuring the availability of a resource that is essential to the health and well-being of the world's ever-growing population.

November/December 2012

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