Welcome back to the #GreenestTee. We’re already halfway through creating the most sustainable t-shirt in the world! So far, we’ve discussed how to design for low impact and the importance of selecting the right fibres.

In this week’s blog, we’re moving on to a high impact area in the supply chain: dyeing. This gets complicated, so hold on!

First, let’s look at the status quo:

If you’re already familiar with dyeing and want to skip to the alternatives, click here .

Currently, 10,000 different dyes and pigments are used industrially and over 700,000 tons of synthetic dyes are produced annually across the world.

Dyeing Impacts Green Story
There are three factors that influence what kind of dyeing you use.

  1. The fiber being dyed,
  2. The dye being used, and
  3. The medium in which the dyeing is going to be done.

What makes it even more complex is that these 3 are all interrelated.[1] The actual process of dyeing has three key steps:

  1. Preparation: where the unwanted impurities are removed from the fabrics,
  2. Dyeing, where color is applied to the textile substrates, and
  3. Finishing, the clothing is treated with chemical compounds to improve the quality of the fabric.[2]

Now, when discussing dyeing in the context of a sustainable supply chain, there are 3 main issues that come up:

  1. It uses up a lot of water! The daily water consumption of an average textile mill for dyeing 8000 kg of fabric is about 256,000 litres.[3] Water is also required to wash the dyed fabrics and clean the machines.
  2. More water pollution! The World Bank estimates that 17-20% of industrial water pollution comes from textile dyeing and finishing.[4]
  3. It takes up a lot of energy! Some of the major energy intensive components include the manufacturing of the dyes and chemicals, heating and drying the products, and treating the wastewater post-dyeing.[5]


GreenestTee Dyeing Green Story


The Alternatives

Given all the harmful impacts of dyeing, what are the alternatives we can use to make our #GreenestTee?

Going au naturel

Believe it or not, it is possible to create beautiful clothing without bleaching or dyeing, and even get colour out of it!

Most people think of clothing made from cotton to be plain white (and boring). However, cotton (and organic cotton!) can actually be grown in a variety of colours, including tan, green, red, brown, and yellow.[6] And these are not genetically modified! No dyes = no wastewater or water pollution created!

Just bleach it!

What about plain white tees? There are 3 modes of bleaching which can be used:

  1. Hydrogen peroxide: It’s not just your hair, hydrogen peroxide is widely used for bleaching cotton fibers. While there’s less water use and is in general safer than dyes[7], peroxide does require high temperature and pressure (more energy use) and needs reducing agents to stop its action.
  2. Ozone bleaching: Ozonization requires lower processing time, uses less water and provided a higher whiteness degree than conventional bleach. However, it does lead to overall weaker fabrics (remember the importance of building to last from our first blog?) and can be harmful to worker health.
  3. Chlorine bleaching (avoid this!): Chlorine bleaching while popular and widely used, has an incredibly negative effect on the environment.[8] Chlorine also degrades the integrity of the fabric, making them thinner with each use and reducing life span.

So sure, you avoid dyes, but as you see above bleaching can be quite harmful as well!

Our blog continues below, but are you interested in keeping up with the #GreenestTee campaign? We’ll have giveaways, for brands and consumers, and a ton of new knowledge. Here’s how you can make sure you don’t miss out:

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Only printing

Hang on, what about just printing on our plain tees?

Both dyeing and printing are wet processing techniques for coloring fabric. However, in dyeing, only one color is produced and can only be done on grey, raw fabric. Printing, on the other hand, can produce various types of colored designs on the fabric surface and can be done on pre-treated, colored fabrics.

The four methods of textile printing are block, roller, screen, and heat transfer printing. Coupled with these methods, there have been new techniques that recover and reuse print paste, which decrease dye and chemical costs as well as the overall pollution load on wastewater systems.

Dyeing with low impact

We get it; you’re not Eminem, you don’t want to wear white tees all the time. So how do we add that bit of colour into our clothes without damaging the environment?

Let’s start with dyestuff (the colour used for dyeing).

There are a few options for this:

  • Low impact dyes (or fiber reactive dyes) do not contain toxic chemicals, are free from heavy metals, require less rinsing, and have a high absorption rate into the fabric of about 70%. Because of these high absorption rates and decreased use of rinse water, these dyes create less waste water.[9] Compared to other dye processes, this dye cycle is shorter and less water, salt, and energy is required.[10] These reactive dyes are comparatively cheap and require less time for dyeing.[11]
  • Natural dyes are obtained from natural sources, most of which are plant origin and others which come from insects, shellfish, and mineral compounds.[12] These natural dyes are resilient to fading and are now becoming more readily available. On top of this, natural dyes provide real social benefits to local communities and societies.[13]
  • Azo dyes (avoid these!) are organic compounds and are used in dyeing cotton as well as silk, wool, viscose, and synthetic fibers. These dyes are easy to use, cheap, and create strong colors. They make up around 70% of the commercial dyes on the market. However, azo dyes are incredibly harmful to both our human health and the health of our environment.[14]

Next, let’s look at the dyeing process.

  • Low liquor ratios: Material to liquor ratio (MLR) is the ratio of the weight of the dye bath to the weight of the goods being dyed. The industry standard for liquor ratio is typically around 12:1 (12 liters to 1kg) for higher quantity dyeing. It’s difficult to have lower lower liquor ratio for high quantity dyeing. So, look out for equipment which can do this. These machines create lower your environmental footprint considerably.
  • Air dyeing: The air-dyeing processes typically involves heating and compressing carbon dioxide, which then enables color pigments to penetrate more efficiently into textile fibers. There are no chemicals or salts, or water discharge and after each batch is dyed. The residue that remains is mainly color pigments and oil.[15]
  • Cold-pad batch system: In cold pad batch dyeing, there is no need to apply heat or use salts during the process. The advantages of cold-pad batch systems are that it requires less water, needs less energy, has a higher percentage of dye fixation, and does not require any salt. However, this is a time intensive process, needs high-quality machinery, and it is hard to fix mistakes.
  • Cationic dyeing. Cationic dyeing begins with the fiber, which is chemically modified to possess a permanent positive charge.[16] By doing so, the dyeing process in cationic dyeing does not require any added salts or other chemicals. This creates a shorter and more efficient dyeing process. The fibre can accept greater varieties of dyes and has more flexibility. It also reduces wastewater, uses less energy, and requires less dyestuffs.

The key takeaway? Efficiency! The best dyeing processes are the most efficient. They use less water, less energy and create less residue (more efficient use of inputs).

Hold on!

Before we start creating fabulous, colorful clothing, there are a few things to keep in mind.

  1. Avoid dark colours in general as they generally have lower exhaustion rates (rate and extent of the dyeing process in total) and so, more dye chemicals and water are required. Colours to avoid: turquoise, bright blues, and kelly greens as these require heavy metals.
  2. Aim to reuse dye-baths for several batches of clothing to reduce waste. This works great for repeat colors and fabrics as well as for clothing that is designed with tonal color patterns.
  3. Check location of the dye house. Is the water being withdrawn from deep aquifers rather than surface water? Is the dye house in water-scarce regions, where too much surface water is being diverted (i.e. India and Bangladesh)? Are there proper government-regulated facilities for cleaning textile wastewater (i.e. ultrafiltration, nanofiltration, and reverse osmosis)? Is the water being used in a closed-loop, rather than new water being added each time?

Asking these questions can help to see the true impact of the dyeing industry and the sustainable changes that can be made.

Don’t know which dyes to use?

Look for these certifications and standards:

  1. OEKO-TEX has the STANDARD 100, which is a worldwide certification system for raw, semi-finished, and finished textile products.[17]
  2. Bluesign is a Swiss organization which provides independent auditing of textile mills and examines the manufacturing processes, from the raw materials to the energy inputs to the water/air emissions as outputs.
  3. Global Organic Textile Standard (GOTS) provides textile processing standards for organic fibers. Their standards include banning chlorine bleaching and azo dyes, and all dyeing processes must keep full records of their usage of chemicals, energy, water consumption, and treatment of wastewater.

Our blog continues below, but are you interested in keeping up with the #GreenestTee campaign? We’ll have giveaways, for brands and consumers, and a ton of new knowledge. Here’s how you can make sure you don’t miss out:

Follow us on our InstagramTwitterFacebook, or subscribe to our newsletter here!

GreenestTee Dyeing Checklist Green Story


Conclusion

So, what does the #GreenestTee look like in the dyeing stage?

There are a lot of alternatives to current dyes and techniques, and the impacts of these can vary widely depending on your manufacturing process. The #GreenestTee would use a more coloured organic fabric, but not everyone can live with that. What would be your pick?

Stay tuned for the next blog as we talk about yarning and weaving!


 

Footnotes:

[1] For example, if the water (most popular medium of dyeing) is contaminated or hard, some of the dyes might separate from the solution, creating spotting and unevenness in the final product.

[2] It is estimated that up to 200,000 tons of dyes end up as liquid waste during the dyeing and finishing operations, which is approximately 10-50% of the total dyes used. Most of this liquid waste ends up in the environment due to the inefficiency in the treatment process as most of these dyes escape systems. The dyes end up in the water bodies and remain there as they have high stability towards light, temperature, and chemicals.

[3] For an average kg of cloth, it is estimated that around 30 – 50 litres of water are needed depending on the dye used. For yarn dyeing, it is estimated that about 60 liters/kg of yarn is needed.

[4] Textile mills discharge millions of gallons of this liquid waste into bodies of water, which is full of color, chemicals, sulphur, naphthol, vat dyes, and heavy metals such copper, arsenic, lead, mercury, nickel, and many, many other harmful additives. This liquid waste changes the composition of the water, prevents the penetration of sunlight necessary for photosynthesis, and interferes with the oxygen transference mechanism. In turn, this halts the self purification process of water, negatively affecting the marine life. With rainfall, this water flows into nearby fields, where it clogs up the pores of the soils and decreases the soil productivity overall.

[5] For example, heating the product during the dyeing process uses 16.6% of the total thermal energy use in the plant and drying the product uses 17.2% of the total thermal energy. In terms of wastewater treatment, removing the color of the compounds from the effluents takes immense amounts of energy as the dyes are designed to resist biodegradation. More specifically, the half-life of a hydrolyzed dye Reactive Blue 19 is around 46 years.

[6] With the rise of inexpensive industrial dyes, growing coloured cotton decreased in popularity as the focus was on generating the largest yield and producing as much quantity as possible. However, we are now in the midst of a revival of growing colourful cotton as many are realizing that naturally colored cotton does not wear out easily or fade away, compared to the synthetically dyed cotton.

[7] Hydrogen peroxide can also be used on other fabrics such as wool, silk, and jute and is safe for at-home bleaching.

[8] One of the most dangerous aspects of chlorine bleach is its persistence, as even low levels of use can accumulate overtime in the air and water and lead to long-term health illnesses.

[9] While these dyes are still synthetic based, they are less dangerous and toxic as compared to other dyes because there are no toxins involved in the process. These dyes are also applied at relatively lower temperatures (about 30 degrees celsius as compared to the 100 degrees celsius used for direct dyes), making it an easy dye to work with.

[10] The entire process also occurs at a pH of around 7.0, which means that no acids or alkalis are added to the water.

[11] Examples of these dyes include procion, ciba cron, remazol, levafix, reactone, primazin, and drimarine and are primarily manufactured in countries such as U.K., Switzerland, and Germany.

[12] The five classic natural dyestuffs include madder, cochineal, weld, clutch, and indigo. Coupled together, these dyes can create essentially any colour desired for the fibers.

[13] The sources of natural dyes include plants (vegetable), insects, and minerals. Dyes derived from vegetable sources are obtained from parts of the plant including the stem, wood, roots, bark, leaves, flowers, and skin. These dyes can produce any shade of colour on both natural and synthetic fibers. Examples of vegetable dyes include logwood, turmeric, and pine wood. Dyes from insects combine with metal salts to create metal-complex dyes. The best red dyes come from insects and some examples of this include lac, kermes, and cochineal. Dyes from mineral sources create colors such as chrome yellow, chrome orange, iron buff, and manganese brown. These mineral colors are actually inorganic and insoluble in water. Examples of these dyes include cinebor, red lead, laminated red earth, and zine white

[14] By releasing azo dye remnants into the air and local water systems, it is shown that photosynthetic activity has decreased in aquatic life and thus, has generated an oxygen deficiency. Azo dyes are also toxic on ecosystems as a whole, causing chronic effects upon organisms such as growth reduction, neurosensory damage, and decreased productivity in plants. Research has shown that the water near these textile industrial plants showed presence of carcinogenic aromatic amines. Without the proper wastewater treatment in place, these harmful cancerous toxins ultimately end up in our drinking water.

[15]  AirDye is another company that is working on air dyeing technology. For their dyeing procedures, the cloth is put into printing machines, instead of traditional water baths. Here, heat and pressure are used to transfer the dyes from paper onto polyester fabric. This process uses 95% less water and 86% less energy.

[16] Most modern-day dyes possess a negative charge. Cotton naturally possess a neutral or mildly negative charge. Thus, when dyeing, the same charges repel each other. This is why salts and alkali are added in order to reverse this positive charge and allow the dyes to bond into the cotton.

[17] It essentially tests for harmful substances in textile products including mordants of heavy metals, phthalates, benzenes, perfluorinated compounds, nonylphenol, and other harmful products.