Colouration without dyes
Sustainable colouration concepts. Part I. Colouration without dyes
This article series will discuss latest trends and future perspectives in colouration technologies. The first part is about colouration without dyestuffs like nature does it. Dyeing and dyes would no longer be required to create colour effects – colouration without dyes.
In recent years the people have been discussing a lot about sustainable textile coloration concepts. The fashion industry and retail brands have started an important initiative towards “zero toxics discharge 2020”, initiated by Greenpeace and supported by big names such as Nike, adidas, C&A, H&M, Puma and others. But not only toxic chemicals, which are major concern of the Greenpeace project, are an issue. A great deal of other chemicals, often not even properly toxicologically assessed, are released to the environment. On the other hand, in big parts of the world, people have lack of clean fresh water which is consumed for agriculture and industry. Textile processing plays a big part in this. During textile processing the effluent is contaminated by chemicals used in the processing (e.g. measured by COD value of the discharged effluent). Zero discharge concepts – recycling and effluent treatments – are implemented in some parts of the industry to avoid contaminated effluents, but usually this happens only when by processing houses are forced by legislation of in case of severe water constraints.
As of today, a great amount of water and energy is consumed to create colour effects on textiles and polymers, it is the backbone of the dyes and pigments industry – dyestuffs for textile applications alone are a business of 1 mio metric tons per annum. All established and prominent technical coloration processes consume water, energy and release effluent which may be treated to avoid discharge to the environment. Unfortunately today, the industry is extremely cost conscious, forced by the sourcing behaviour and the buying power of the big retailers and by large overcapacities of dyes & chemicals suppliers. This resulted in a market shift to Asia, and a preference for fit-for purpose and commodity products being applied rather than using best available technologies.
When we look into the future, the established coloration methods have to be further optimized in terms of dye exhaustion-fixation yields as well as water and energy consumption by state of the art equipment and by selection of best practices and improved dyes and chemicals.
Ideally, a fully sustainable coloration process is low-energy, waterless and does not require any chemicals.
Do we really need dyes and chemical to create colours ? Colouration without dyes is potentially a hot topic in the future. Nature does not need any synthetic dyes and chemicals. A good example in nature is the Morpho butterfly. The Morpho butterfly butterfly creates a vibrant blue colour throughout their lives without any dye or pigment. The scales on their wings are made of many layers of proteins that refract light in different ways, and the color we see often is due entirely to the play of light and structure rather than the presence of pigments.
Scientists try to lean from nature and try to imitate this effect. The challenge is big, yet the endeavour is worth the effort – the result would be coloration without any chemical, without water consumption, and without any effluent.
Through nanotechnology a new chapter has been opened to create colour effects. The Japanese company Teijin Fibers has developed the Morphotex® fibers imitating the same effect.
The Morphotex fibre is based on nylon or polyester, available in four basic colours red, green, blue and violet. No dyes or pigments are used. Rather, color is created based on the varying thickness and structure of the fibers. Energy consumption and industrial waste are reduced because no dye process must be used.
The Morphotex fibre (see details Morpho fibre, KENKICHI,N. : Annals of the High Performance Paper Society, Japan 43, 17-21 (2005)) was launched in 2005, however, reportedly the manufacturing of the fibre was suspended in 2011. The colour effects were pale and fibres very expensive. It seems consumer awareness is not developed to a point where people would really be prepared to pay high premium prices for such a specialty product. For today´s market, the cost of manufacturing such special fibres is not yet competitive.
EMPA in Switzerland is an interdisciplinary research and services institution for material sciences and technology development within the ETH Domain. EMPA has published interesting work (EMPA paper) to create colour effects by optical effects, through light interference on the surface of precisely structured nano surfaces, on fabrics such as polyamide, polypropylene or polyester. The process to achieve said nano structures is called roll embrossing applying nano structures of nickel. However, it seems to be a long and winding pathway until commercially feasible structures can be manufactured by this technology for the application on textile fabrics. The cost of the necessary equipment and the cost of production will be too high for mass commercialization of the so coloured textiles. For now, the technology is considered as a niche for creating special optical colour effects for fashion articles. Not only from academic point of view this development is highly interesting.
In non textile applications, scientists at Simon Fraser University and NanoTech Security have reproduced a colour effect for anti-counterfeiting technology by means of nanotechnology, to replace holograms on banknote and to authenticate legal documents (NanoTec). Again here, the Morpho butterfly was giving the template in nature that inspired innovation. “The Morpho’s wing absorbs light and gives off the color,” NanoTech Security CEO Doug Blakeway told TechNewsWorld, “but there’s no color pigment — there’s nothing like a dye or anything else. It’s a hole that traps light and releases color.”
In hair coloration, in ancient Egypt, 2000 years ago, nano crystals of lead sulfide were used for hair coloration. Today´s hair dyeing coloration methods are somewhat critical, involving chemicals such as p-phenylene diamine (PPD). It is a good question whether this is really a more sustainable process because of safety concerns related to the use of the chemical – PPD is an aromatic amine which are generally known to cause bladder cancer, it is known to bronchial asthma, sensitize dermatitis and it is allergenic, even voted Allergen of the Year in 2006 by the American Contact Dermatitis Society.
Future hair coloring techniques may include nano-sized colorants (nano hair dyeing) which will penetrate the hair and remain trapped inside for longer-lasting hair coloration. Scientists also are developing substances that stimulate the genes to produce the melanin pigment that colors hair. These substances promise to produce a wider range of more natural-looking colors, from blond to dark brown and black without toxicity but with more natural results.
Also with the help of nanotechnology, researchers at BASF (BASF podcast, BASF ) have develop colours that change their colour impression when viewed from different directions. Even more effects are possible; these so called “mechano optical colours” change their colour when you stretch them and since the color comes from the structure of the material instead of a dye, it will not fade over time.
In the next article of this series we will go back to textile processing applications and focus on alternative dyeing technologies and fibre modification processes to improve the dyeability while saving water and energy through the dyeing process.
Another option is to improve the dyeability of textile fibres by either a chemical modification or by bio-engineering. Especially in cotton this is a major challenge because of intrinsically incomplete exhaustion and fixation rates.
Moreover there is scope for novel coloration technologies, waterless and recycling dyeing methods such as dyeing polyester fibres from dyeing from supercritical carbon dioxide (CO2).
To be continued.