Humans have been colouring fabric for thousands of years. Nature provided the natural pigments for fabric dye until 1856 when WH Perkins discovered the use of synthetic dyes. Now, 90 per cent of the world’s textiles are dyed synthetically and it has become a gigantic industry. In this article, we will discuss the current issues related to textile dyeing & treatment, and explore new sustainable dyeing technologies.

The Problem with Conventional Dyeing Practices

Pollution

Usage of synthetic dyestuffs has adverse impacts on all forms of life. The existence of vat dyestuffs, nitrates, acetic acid, soaping chemicals, enzymatic substrates, chromium-based materials, and heavy metals as well as other dyeing ingredients, makes the textile dyeing water extremely toxic. Other hazardous chemicals used in dyeing include formaldehyde-based colour fixing auxiliaries, chlorine-based stain removers, hydrocarbon-based softeners, and other non-biodegradable dyeing adjuvants. 60-80 per cent of all dyes are AZO dyes, many of which are known to be carcinogenic. Chlorobenzenes are commonly used to dye polyester, and are toxic when inhaled or directly in contact with skin.

Water and energy consumption

Excess water consumption is another huge issue associated with synthetic dyeing. Dyeing cotton is particularly water-intensive, as it is estimated that dyeing and finishing can use around 125 litters of water per kilogram of cotton fibres. Not only does it require huge volumes of water, but it also relies on substantial amounts of energy to heat up water and steam that is necessary for the desired finish.

The demand for change

As more consumers become aware of the harmful effects of current dyeing practices, new technologies make way for more cost-effective, resource-efficient, and non-polluting sustainable dyeing alternatives. Innovation in dyeing technologies ranges from pre-treatment of cotton, pressurised CO2 dye application, and more recently, the creation of natural pigments from microbes. Current dyeing innovations can help reduce water usage, replace wasteful practices with efficient and cost-effective ones, and minimise the impact on our ecosystems.

Waterless technologies for sustainable dyeing

Cotton

The dyeing process of textiles varies greatly depending on the type of fabric. Cotton dyeing has one of the longest and most water and energy-intensive processes, due to the negative surface of cotton fibres. This means that usually cotton only takes up about 75 per cent of the dye that is used. To make sure colour holds, dyed fabric or yarn is washed and heated repeatedly, producing huge amounts of wastewater.

Huntsman, one of the world's largest dye suppliers has developed a line of dyes for cotton called Avitera that bonds to the fibre more readily. According to the company, the colours require one-quarter to one-third less water and one-third less energy. The technology used means the dye step lasts about four hours, compared with seven hours for conventional dyes.

Colorizer technology works by altering the molecular structure of the cotton fibre before it is spun. When Colorizer’s treatment is applied to the surface of raw cotton, the technology reverses the charge of the cotton, allowing the dye to quickly and easily bond with it. That’s what allows Colorizer to eliminate the need for the toxic chemicals that otherwise are required in modern dyebaths. This pre-treatment speeds up the dyeing process, reduces 90 per cent of water usage, requires 75 per cent less energy and 90 per cent fewer chemicals that would otherwise be needed for effective dyeing of cotton.

Polyester

Dyeing synthetic fibres, such as polyester, is a shorter process and 99 per cent of the dye that is applied is taken up by the fabric. However, this does not mean that current dyeing practices are more sustainable. Air dye technology is improving on this process. Air dye uses dispersed dyes that are applied to a paper carrier. With heat alone, Air Dye transfers dye from the paper to the textile’s surface. This high heat process colours the dye at a molecular level. The paper that is used can be recycled, and 90 per cent less water is used. Also, 85 per cent less energy is used because the textiles do not need to be soaked in water and heat dried over and over.

Dye coo uses CO? to dye textiles in a closed-loop process. “When pressurised, CO? becomes supercritical (SC-CO?). In this state CO? has a very high solvent power, allowing the dye to dissolve easily. Thanks to the high permeability, the dyes are transported easily and deeply into fibres, creating vibrant colours." DyeCoo technology does not require any water, and they use pure dyes with 98 per cent uptake. Their process avoids excess dyes with harsh chemicals and no wastewater is created whatsoever during the process. They have been able to scale up this technology due to commercial endorsements from both textile mills and end-users.

Natural pigments from microbes

Most of the clothing we wear today uses synthetic dyes in its production. The problem with these is that valuable raw materials, such as crude oil are needed during production and the chemicals added are toxic to us and the planet. Even though natural dyes are less toxic than synthetic dyes, they still require agricultural land and pesticides for the plants that made up the dyes.

Labs across the world are working with bacteria to find new innovations in dyeing. Streptomyces colocolo is a microbe that naturally changes colour based on the pH of the medium it grows inside. By changing its environment, it is possible to control what type of colour it becomes. The process of dyeing with bacteria begins by sterilising a textile to prevent contamination, then pouring a liquid medium filled with bacterial nutrients over the textile in a container. Then, the soaked textile is exposed to bacteria and is left in a climate-controlled chamber for a couple of days. As the bacteria grows, it ‘live-dyes’ the textile. The textile is then washed, then let to dry. Bacterial dyes use less water than conventional dyes and can be used to dye many different patterns with a vast range of colours.

Also using bacterial strains is Faber Future, a UK-based lab. Bio designer Natsai Audrey Chiesa has identified a way to program Streptomyces coelicolor to create a large range of colours that can be used to colour both synthetic and natural fibres (including cotton).

There is certainly still a long way to go, however, these technologies and innovations can lead the way to a healthier planet. In order for these technologies to thrive and scale up to a commercial level, it is important that we drive investments and partnerships between these companies, and pressure existing fashion and chemicals companies to make the necessary changes.