Dope, Spin or Solution dyeing
Since polyester fabric was popularised in the mid-20th century it has been dyed using the age-old wet dyeing process designed for natural fibres. This is a waste of energy and resources as synthetic fibres can be coloured in the one-step dope dyeing process that introduces pigment, in the form of colour chips, to the liquid polymer solution before it is extruded into fibres. This means the pigment becomes part of the fibre, resulting in superior colour fastness and consistency. According to Swedish company We aRe SpinDye, their dope dyeing process consumes 75% less water and 90% less chemicals, while improving energy consumption and reducing carbon footprint by 30%.
In 2018 Norwegian textile company Expert Fibres launched IndiDye®, a revolutionary plant dyeing solution for cotton and tencel that requires significantly less water and achieves an unprecedented level of colour fastness – without chemicals or fixatives. As with dope dyeing, the pigment is introduced at fibre level before the yarns are spun: liquid plant dyestuff and batches of fibre are put into baths where they are exposed to ultrasonic sound waves that push the dye into the fibre core. This technique creates no waste water, improves energy efficiency and cuts down on emissions with lower temperatures and shorter dyeing times.
US-based Indigo Mill Designs, Gaston Mills and Spanish textile mill Tejidos Royo are collaborating to transform the denim industry with a dry indigo dyeing technique. Launched last year, the patented IndigoZERO process uses foam to dye the yarn, where air transports the dye onto the fabric instead of water. Compared to traditional rope dyeing, IndigoZERO consumes 99% less water, allows for small lot sizes and is carried out in a machine four times smaller than a typical indigo dyeing machine. Classic denim brand Wrangler are the first to adopt this technology and will be launching a foam-dyed collection later this year.
Cutting out water and processing chemicals completely, Dutch company DyeCoo uses carbondioxide to dye synthetic fabrics on an industrial scale. In the dye vessel, the CO 2 is heated and heavily compressed to reach a supercritical state between a gas and a liquid, which makes it very solvent. This allows the dye to dissolve easily and penetrate deep into the fibre. The efficient colour absorption and short batch cycles cuts energy usage by half, what’s more, the CO 2 used is reclaimed from existing industrial processes, and up to 95% is recycled.
London biodesign lab Faber Futures, as well as the Vienna Textile Lab and the research project Living Colour, have obtained colour from naturally pigment-producing bacteria to dye both natural and synthetic fabrics. The process requires very little water, low temperatures, no chemicals or fixatives, and doesn’t generate any polluting byproducts. Growing bacteria is also far less resource-intensive than cultivating dye plants, while the biodegradable pigment is kind to humans and the environment, even possessing antimicrobial and UV-protection properties. Scaling things up , French startup Pili and Colorfix in the UK have bio-engineered bacteria to carry colour molecules, which then undergo fermentation to produce large quantities of pigment.
Almost half the world’s coloured thread remains unused, ending up in landfill or incinerated, according to Israeli company Twine, who have created a digital on-demand thread dyeing system that transforms white thread into any colour, to the required length. The system, much like a printer, only needs a standard electrical outlet and ink, doesn’t use any water, and beingon-demand, eliminates waste and dead stock. Over in Hong Kong, Intech Digital Technology can, for instance, print onto plain fabric the pattern pieces for a pair of “distressed” jeans, ready to be cut out and assembled. Using reactive pigment technology, their dye- and water-free ZERO-D digital print solution produces no pollution, minimises waste and has no MOQ.
Some dyeing processes are more suitable for specific fibres, quantities and even types of garment. Although it might be easy to dismiss petroleum-based synthetic dyes, the lasting pigment can help enhance garment performance and lifetime. Natural dyes may not have the same staying power or vibrancy, yet for fabrics like denim where a worn-in look is often sought, the indigo dye need only cover the fibre surface so that it can chip off to develop a unique patina. As awareness continues to grow, dye manufacturers are increasingly phasing out harmful chemicals and treating waste effluent to lessen water pollution. Perhaps in the not-so-distant future , bioengineering pigment into natural fibres will become the norm, however in the meantime, investing in friendlier, resource-saving dye technologies is better for both business and the environment.
Next Instalment: Biomimicry – Textiles and processes inspired by nature, from 4D fabrics to fast cycles.
Written by Mairi Hare as part of a collaboration between Sourcebook GmbH and Texpertise Network.
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