ColorZen fibre – the future of cotton dyeing

Tony Leonard, technical director, ColorZen

www.wtin.com

ColorZen is providing the opportunity to change cotton dyeing to the most environmentally friendly and sustainable method available to the textile industry today. The dyeing procedures of ColorZen-treated cotton fibre result in large verifiable savings in water, energy, dyes, and dye cycle times. It also eliminates the need for potentially toxic chemicals to be added to the dyebath, allows for salt-free dyeing, and results in a cleaner wastewater stream. The dyeing of ColorZen fibre is a major leap forward when compared with conventional cotton dyeing procedures.

Tony Leonard (right) in discussion with Jeff Marks, from ColorZen’s manufacturing partner, Jabil Inc

In the traditional dyeing of cotton goods, reactive dyes are the dyes of choice because of their overall fastness properties. Reactive dyes allow a wide range of achievable colours. The use of reactive dyes on cotton requires salt to neutralise the slight negative charge of the cotton and force exhaustion of the soluble dyestuffs. Because of a competing hydrolysis reaction reducing the fixation of the reactive dye with cellulose, there is always unfixed or hydrolysed dye left on the fabric that must be removed by rinsing after dyeing.

Excessive amounts of water are required with conventional reactive dyeing of cotton, not only to dilute and remove the salt needed for dyeing, but to also remove the hydrolysed dye from the fabric so that acceptable final fastness properties can be obtained.1-3 As a result of the large amounts of salt and water used with traditional fibre reactive dyes, cotton dyeing has become notorious for its consumption of raw materials and natural resources.18 In addition, the discharge or disposal without proper treatment of the large quantities of salt used in dyeing can be extremely toxic to aquatic life and the environment.

Diverse approaches

Many diverse approaches and technologies have emerged that seek to address the issues found with conventional reactive dyeing of cotton, including: low liquor ratio dyeing machines; smart rinsing technologies;1-2 high efficiency reactive dyes;4-9 neutral pH dyeing of cotton;10 cationic reactive dyes;11-12 and real-time dyebath monitoring.13 The drawback with most of these types of innovations and technologies is the capital required to utilise such concepts.

In a highly competitive global market, many textile dyers are not ready to spend significant capital on new equipment, especially not when they are already operating with maybe inefficient but known and tested dyeing equipment. Further, the additional and different synthesis steps required to develop more efficient reactive dyes often mean that new, higher-yield dyes end up costing the mill or dye house more than conventional reactive dyes.

Many types of innovations in cotton coloration have not been, or cannot easily be, translated into real processes or applications for production. However, cationic cotton technology is increasingly being recognised as the most practical sustainable alternative to traditional reactive dyeing of cotton.18

Regardless of the type of cationisation reagent used to pretreat the cotton, once the cotton is cationised, it possesses permanent cationic sites resulting in cotton with positive charges.18 The positive charges allow cotton to be dyed with anionic dyestuffs without salt and can achieve up to 100% dye utilisation. By eliminating the use of salt and increasing dye utilisation, significant raw material and consumable savings are possible when producing dyed cotton goods.14-16 However, even with the promised environmental benefits, cationised cotton dyeing has not, to date, been scalable or had wide industry acceptance; that is, until the introduction of ColorZen cotton fibre.

 

Cotton knowledge

ColorZen has used its previous cationic cotton knowledge and refined it with its patented technology to create cellulose fibre that has permanent positively charged amino dye sites. This is accomplished by carefully reacting a quaternary ammonium compound with the cellulose molecule to create this permanent site. Cotton fabrics produced with ColorZen-treated fibres are easily dyed with anionic dyes, without salt. Many anionic dyes can be used, while maintaining good colourfastness, including reactive, direct, and acid dyes.

ColorZen’s unique application process assures uniformity of these dye sites and thus levelness in the future dyeing of the cotton. Understanding that trying to conduct this reaction in customers’ plants could easily result in variations of individual treatments, ColorZen built its production model so that all chemical ratios and aspects of its closed system are continuously monitored and recorded. This, and rigorous quality assurance, help ensure that the dyeability and spinning characteristics of every bale of ColorZen fibre shipped is equal to the previous and to the next.

It is also important that the savings that using ColorZen fibre generates, in dyeing, are not negated by excessive consumption of resources in the treatment of the fibre. For this reason, our production lines have been designed for maximum utilisation of the chemistry and minimum discharge to the environment. The total plant wastewater represents only a small fraction of the total water and energy savings achieved with the efficient textile dyeing process available with ColorZen cotton.

 

Verifiable savings

Dyeing ColorZen fabrics has shown verifiable savings of up to 90% less water, 75% less energy, 95% less chemicals, 30-50% dye savings, and dye cycle time reductions of up to 70%. The elimination of the critical addition steps for salt and alkali, and the excessive hot soaping necessary to remove salt and hydrolysed dye from dyed fabric with conventional reactive dyeing, is the primary source for these savings. A simpler ColorZen dye procedure results in the shorter dye cycle time.

Fabrics produced with ColorZen fibres will dye quicker and easier than regular cotton or many other fibre types. They dye at lower temperatures and use less overall water and energy than a traditional cotton dye cycle. No salt and minimal soda ash are required to complete the dyeing process. Depending upon the equipment used, the typical dye cycle from load to unload takes only 3 hours and 30 minutes.

Liquor ratio is not critical in the dye exhaustion of anionic dyes on ColorZen fibres. Larger volume dye equipment is similarly efficient to low liquor ratio dye machines in obtaining complete dye exhaustion. High dye exhaustion up to 95% of dark shades with ColorZen fibre not only reduces wastewater treatment requirements, but also makes available the opportunity to reuse dyebaths. These differences generate ColorZen’s environmental benefits, but they also mean certain measures must be observed in the (cleaner, more efficient) dye procedure.

 

Positively charged

The establishment of the natural attraction of the dye to the now positively charged ColorZen cotton means that the initial strike of the dye should be controlled. There is minimum migration of dye molecules after ionic bonding with the ColorZen dye site. The rapid dye strike can be slowed with temperature and time, but a retarder can also be used. Several anionic retarders have shown success in this regard. These retarders will occupy dye sites and allow the dye to evenly exhaust as the temperature is raised.19

A polymeric lubricant is also recommended in the dyebath. This allows the fabric to move better during all stages of dyeing, avoiding ‘rope marks’. As ColorZen fabrics dye much faster than conventional cotton fabrics, the lubricant ensures good fabric movement and an even strike on the fabric in its rope form in the machine.

Like salt, soda ash is not necessary to exhaust reactive dyes on ColorZen fibre. However, due to the nature of some dyestuffs, a small amount of soda ash can be used for colour development. Typically, only 2-5% soda ash is required.

 

Universal density

ColorZen cotton is shipped to customers as treated fibre in standard, universal density (UD) bales. ColorZen fibre can be spun into any yarn count. ColorZen fibre can also be blended with non-treated cotton fibre to produce a 100% cotton mélange or heather fabric that is piece-dyeable, allowing the production of ‘dye on demand’ heather greige which can be used to produce a variety of colours as needed. In these fabrics, the ColorZen treated fibres will accept colour while the untreated fibres will remain undyed.

Piece-dyeable stripes and other effects are also possible: 100% ColorZen fibre, or heather blends, can be alternated with untreated cotton to produce a greige striped fabric that can be dyed, later, and in multiple colours. Garments made with ColorZen cotton fabric can be dyed after formation to meet ‘speed to market’ demand.15 Using a sewing thread made with ColorZen in the garments will allow dyeing of the same sewn design in multiple colours, while maintaining the chosen colour throughout the garment.

Cotton dyeing has been around for centuries, and many innovations over the years have tried to correct its harmful environmental effects, but with limited success. Saving water, reducing energy use, and obtaining zero toxicity are widely espoused as the new global goals of the textile industry. These are also the goals of ColorZen, goals that can be substantially realised by using and dyeing ColorZen treated cotton.

Brands and retailers, and their production mills, now have the opportunity to partner with ColorZen to provide consumers with truly sustainable coloured textile products, and usher in a new era for cotton and the environments in which it is dyed.

 

References

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  3. Hoffmann, F., et al. “Washing Off Reactive Dyeings in Jets with Bath Change Rinsing and Continuous Rinsing.” Melliand International. 4. (1998): 223-226.
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  10. Lewis, David M., et al. “Covalent Fixation of Reactive Dyes on Cotton under Neutral Conditions.” AATCC Review. January 2008, p35.
  11. Hinks, David, et al. “Cationized Fiber Reactive Dyes for Cellulosic Fibers.” AATCC Review. May 2001, p43.
  12. Lewis, D. M. and L. J. Sun. “Quaternary Reactive Dyes Containing a Thioether-ethylsulphone Group. Part 1: Synthesis of a Trimethylammonium Ethylsulphide-ethylsulphone Dye.” Coloration Technology. 119. (2003): 286-291.
  13. Farrell, M. et al. “Real-Time Monitoring For Sustainable Fiber Reactive Dyeing Processes.” AATCC Review. September/October 2011, p44.
  14. Hauser, Peter J. and Adham H. Tabba. “Improving the Environmental and Economic Aspects of Cotton Dyeing Using a Cationized Cotton.” Coloration Technology. 117. (2001): 282-288.
  15. Leonard, Tony M. “Cationized Cotton – ‘Fact or Fiction?’”
  16. Thiry, Maria. “Color It Greener.” AATCC Review. May/June 2010, p34.
  17. Rupin, Michel. “Dyeing with Direct and Fiber Reactive Dyes.” Textile Chemist and Colorist. 8. (1976): p139.
  18. Farrell, Matthew J. “Cationic Cotton, Reservations to Reality”
  19. Fu, Sha & Farrell, Matt & J. Hauser, Peter & Hinks, David & J. Jasper, Warren & Ankeny, Mary. (2017). Real-time dyebath monitoring of reactive dyeing on cationized cotton for levelness control: part 2—effects of leveling agents and dye dosing. Cellulose. 10.1007/s10570-017-1291-0.

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