Professional guide

Dyeing

The colorful world of dyes is not all fun and games.

One of the most troublesome current areas of concern in the textile industry is the pollution brought about by the coloration processes of dyeing and printing. The main problem is that the compounds used for applying color are almost always highly toxic, carcinogenic or both.

Up until 1856 all textiles were dyed with natural dyes. Nowhere in the world do industrial natural dye-works, which could handle a department store-sized order, still exist. But until very recently, India, Indonesia, Pakistan, Egypt and all of Central and South America were dying naturally on an industrial scale. In those regions, vestiges of equipment and expertise still remain. Natural dyes are usually derived from plants and the amount produced is tiny, requiring huge areas of land to produce small quantities at high cost. It has been calculated that even if two thirds of the world's agricultural land was used to grow natural dyes there would be scarcely enough to dye the current volume of textiles. Dyes from animal sources fare even worse and would never be commercially viable. There is also the question of mordants, which are metallic salts. There are a few natural dyes that can give bright colors and reasonable technical performance without the need for a mordant, such as Turmeric, but their number is limited. In the last years, though, there has been a growing interest in natural dyes.

Most synthetic dyes are based on raw materials that are derived from petroleum and this issue remains, even though dyes have become much safer than in previous generations. There is still an under-class of dye manufacturers who continue to make cheap, nasty, synthetic dyes that do cause serious health risks to the environment, workers and to a lesser extent, consumers. Azo-free dyes are a minimum requirement, but new developements in dyeing give us reason to be optimistic.

New research
It could be that researchers at the University of Leeds have found the perfect mix between nature and synthetics. They take natural dye molecules and then chemically modify them to produce natural/synthetic hybrids. With reatively simple modifications they create a molecule that produces bright, high fastness disperse dyes for polyester and PLA: They have also worked with creating colored polymers inside textile fibres in a patented catalytic dyeing process. Simple colorless molecules, some derived from natural starting materials, are linked together and the color develops as the polymer chain grows. The process has been very successful on hair fibres such as wool, and can be carried out cold which is great news from an energy perspective.

GOTS-approved dyes
DyStar was one of the first companies to have its dyestuffs approved by GOTS for organic textiles. DyStar now offers an extensive range of dyes and auxiliaries which are approved to GOTS Version 2.0. DyStar experts in cotton processing have defined how to use GOTS-approved products to achieve sustainable and optimized results in organic cotton processing using Best Available Technology in pre-treatment, dyeing and finishing.

Problematic shades
Achieving deepest shades on cellulosic fabrics like cotton can sometimes take a big toll on the environment. Because certain reactive dyes in yellow, red, and black shades can interact and “block” each other from fixing onto the fabric, it can take a lot of dye to attain darker shades like brown and black – and much of that dye is wasted because it doesn’t fix to the fabric, but washes down the drain. To counter this DyStar has developed Remazol Ultra RGB reactive dye technology, which is particularly designed for the problematic deep shades on cotton. High fixation keeps the dye on the fabric, where it belongs, instead of in the waste water. More dye on the fabric instead of down the drain also means savings of dye, chemicals, water, and energy for production. (Source: Wagner, Whitepages, EcoTextileNews, DyStar)