Textile manufacture A shade of green Major retailers are starting to consider the environmental impact of the fabric dyeing and finishing processes used by their manufacturers. Fiona Case reports

In March this year researchers converted into other hazardous these goals are solutions which from the environmental activist In short substances, or accumulate in wastes progressively replace hazardous group completed  Hazardous chemicals generated during the treatment chemicals with less hazardous, a project to collect wastewater were found in the process (such as sludges),’ explains and preferably ultimately non- samples from two Chinese textile wastewater of two Kevin Brigden, a scientist at the hazardous, alternatives.’ manufacturing facilities which Chinese textile Greenpeace Research Laboratories, produce for a number of manufacturing plants based at the University of Exeter, UK. Hung out to dry international brands including earlier this year The Greenpeace Dirty Laundry The perfluorinated compounds Abercrombie & Fitch, Calvin  Some international report, published in July, stirred (PFCs) probably came from water Klein and Lacoste. The facilities clothing retailers up interest. ‘A number of large repellent textile finishes. ‘PFOA – located on the river and and brands are now textile brands are now making seems to be particularly problematic Pearl river deltas – had modern looking to improve commitments to eliminate the use and one solution is to switch to wastewater treatment plants, but gas their environmental of hazardous chemicals within the C6 material,’ says Martin Bide chromatography-mass spectrometry credentials their supply chains,’ says Brigden. from the department of textiles at analysis of their effluent revealed  Research to eliminate ‘What is required to achieve the University of Rhode Island, US. the presence of undesirable bioaccumulative and compounds including a range of toxic compounds, perfluorinated compounds such and to improve the as perfluorooctanoic acid (PFOA: environmental footprint an environmentally persistent of textile dyeing and and bioaccumulative chemical finishing is of increasing with a range of toxic effects), interest nonylphenol (a persistent material considered to be an endocrine disruptor), toxic dichloroaniline, aminoanthraquinone and aromatic amines including 2-methoxyaniline (a known carcinogen). ‘Many persistent organic Water sampling from pollutants will either pass through the discharge pipe at the the conventional wastewater Youngor Textile Factory

QUI BO/GREENPEACE QUI treatment plants unchanged, be on the Yangtze river delta 48 | Chemistry World | December 2011 www.chemistryworld.org SHUTTERSTOCK

‘In 2006 the US Environmental final coating is only nanometres Textile dyes in a range of photons with wavelengths between Protection Agency approached thick – and material that is not colours on a market stall 400 and 700nm. The charge on the the eight largest fluorocarbon coated onto the product is entirely molecule and its substituents define producers and requested a 95 per contained,’ Coulson explains. the type of dye and the materials on cent reduction in PFOA use by ‘Conventional chemistries such as which it will be used. 2010, and 100 per cent by 2015. The PFOA are not required and there are The first synthetic dye was major companies have responded no issues with waste.’ P2i are now discovered serendipitously in 1856 and have already transitioned their coating more than 1.5 million pairs of by the young William Perkin while textile finishing products to short- high-end per year for brands he was trying to make quinine. chain chemistry.’ such as Timberland, Mizuno and Perkin’s mauve was a water- Use of these new materials would Teva, and are in discussions with soluble cationic dye. This class is reduce the PFOA in the effluent, but several clothing brands. still used for dying acrylic fibres Brigden is not satisfied. ‘The shorter Nonylphenol in the wastewater (the proposed mechanism is salt chain PFCs also have properties of almost certainly resulted from formation with anionic groups concern, and have already been found the degradation of nonylphenol on the fibres). Cellulosic fibres to bioaccumulate in the wild. The goal ethoxylate (NPE) surfactants. It such as cotton, viscose, or lyocell needs to be the elimination of PFCs.’ did not need to be there. ‘The use are often dyed using reactive P2i, a company focusing on liquid of NPEs in textile manufacture is dyes. As their name implies, the repelling nanocoating technology no longer permitted within the chromophore is attached to a group based in Abingdon, UK, is taking a EU, which clearly demonstrates such as a halogenated heterocycle step in that direction, according to the ability to manufacture textiles or an activated double bond which its chief technical officer Stephen without them,’ says Brigden. reacts with the hydroxide group Coulson. ‘We apply fluorinated ‘It is unfortunate that NPE use ‘Many on cellulose. Because they are acrylates to surfaces using plasma continues in other locations, and chemically bonded the reactive technology,’ he says. The technology that many brands allow their pollutants dyes have excellent colour fastness, was developed to provide maximum products to be manufactured using pass through however some of the older water and oil repellency for military these substances.’ materials can have fixation rates clothing. Acrylate monomers with wastewater as low as 50 per cent. Half of the fluorocarbon side chains are fed Dyeing to be green treatment dye ends up in the waste stream. A into the plasma. They deposit on the Dyes are typically large aromatic wide range of techniques including surface and polymerise. ‘We are only molecules with delocalised orbitals plants micro- and nano-filtration, using tiny amounts of material – the of appropriate energy to absorb unchanged’ photocatalytic oxidisation, sorption www.chemistryworld.org Chemistry World | December 2011 | 49 Textile manufacture methods and bioreactors have (the amount of dye that ends up ‘We abandoned using acid dyes, large multicyclic been used to remove the bright chemically bonded to the fibre). aromatic molecules with anionic colours from the effluent. ‘The last ‘In the past as much as 25 per cent chrome dyes a sulfonyl or amino functionalities, example I saw used plasma-treated of the physically absorbed dye did long time ago’ applied in an acidic dye bath. These onion skins,’ comments Bide. But a not chemically bond. This material materials are often mordanted with better approach is to optimise the ended up in the wash bath, six to chromium – which is of considerable chemistry. eight baths at high temperature concern in wastewaters. ‘We ‘We provide a range of dyes which were necessary to remove it. For abandoned chrome dyes a long have combinations of several, often our new dyes three or four baths time ago, although they may still be different, reactive groups on each at 60°C are sufficient. More than used in other parts of the world,’ chromophore,’ explains Patrice 90 per cent of the dye ends up says Carreau. ‘The new reactive Carreau, director of technology and chemically bonded to the fabric,’ dyes provide colours that are even project management at Huntsman explains Carreau. deeper than the chromes on wool or Textile Effects (headquartered Sulfur dyes used to be the main the sulfur dyes on cotton.’ in Singapore). ‘The dyes all have choice for dark black shades on Alenka Majcen Le Marechal is identical kinetics of absorption cotton. In a classic sulfur dyeing a professor at the University of and reaction – so that the final process the S–S bonds are reduced Maribor, Slovenia. She studies the colour created by a mixture is with Na2S producing soluble dye effluent from the textile industry as consistent throughout the fabric. anions which absorb into the fibre part of the European Aquafit4Use The light- and water-fastness must and are reoxidised to their insoluble project. She is still concerned also be consistent so that the colour form. While some dye suppliers about reactive dyes. ‘They are remains true as the fabric is worn have managed to greatly reduce not dangerous in themselves, and washed.’ the release of environmentally but their synthesis involves Huntsman aims to optimise both problematic sulfides in effluent, precursors and side products that the exhaustion rate of the dye (the others recommend moving to are toxic.’ The dichloroaniline amount of dye that is absorbed reactive dyes. Wool, silk, and nylon and aminoanthraquinone onto the fibre) and the fixation rate have traditionally been coloured observed by Greenpeace could have come from this source. ‘We are seeing increasing amounts of Catalytic clothing these toxic materials in the final Technologies are being product, particularly in recent developed to mitigate the years as the production of textile negative impact of textile dyes has moved from the EU to manufacture, but can our other countries,’ she says. ‘These clothes make a positive impact impurities can be released into on the environment? wastewater during textile finishing, Tony Ryan, pro-vice or even during home laundering.’ chancellor at the University of Cellulosic fibres are also dyed Sheffield, UK, believes they can. using vat dyes. The insoluble Working with artist and designer chromophore is reduced to its Helen Storey he hopes to colourless, but water-soluble form convince us all to wear clothing and absorbs into the fabric. Once coated with nanoparticles of the fabric is removed from the TiO2, so that together we can bath the material rapidly oxidises make a significant reduction in back to its coloured form. ‘The NOx pollutants. dye molecule isn’t the issue for Air pollution is a significant this system. More than 90 per problem. It is estimated to cent of the material agglomerates

NIK DAUGHTRY NIK reduce the life expectancy within the fibre,’ says Thomas of every person in the UK by Field of Jeans at Chelsea College of Art and Design in September 2011 Bechtold, professor at the Research an average of 7–8 months. ‘I Institute for Textile Chemistry calculated the surface area of Tom Domen, long term how to present the concept.’ and Textile Physics, University of the fibres making up my suit innovation manager for the To promote their work, the Innsbruck, Austria. ‘But there is and realised that clothes could ecologically sound cleaning team is planning a number of no way to recover reducing agent be a catalyst support with high products firm Ecover, Belgium, artistic installations of TiO2- in current processes. A typical specific surface area. Coating has been working with Ryan’s coated clothing during 2012, reducing agent is dithionite. We TiO2 onto the surface of clothing team. ‘We have already started including the their Field of use electrochemistry to reoxidise fabrics at the same surface work on a laundry product – we Jeans in Durham in March, this material and membrane filters density as photocatalytic are leaning towards a one-time and exhibiting a crop of kilts to concentrate it so that it can be architectural coatings could softener-like additive,’ he says. at the Edinburgh International reused. I am convinced that this make a significant difference,’ ‘We have treated textiles in Science Festival. ‘We are approach has potential,’ he says. says Ryan. ‘One square metre laundry and we are determining also hoping to gather a group of wall can take out 0.5g NOx the optimum amount of TiO2 of catalytic clothing users More environmentally distressed a day so even with 3/4 of the to add. We will then send the together in London during the Indigo, the dye used for jeans, is coated fibres in the dark we can product to be tested for its NOx Olympics and use satellite NOx a less substantive example of a anticipate a person wearing removing ability. We still have a imaging to see the difference vat dye. But, after successfully catalytic clothing taking out at lot of R&D to do, but we also need that they make to the air that adsorbing the dye in the fabric, least a gram of NOx a day.’ to talk to the consumers to decide surrounds them,’ says Domen. denim manufacturers proceed to remove some of it again, at 50 | Chemistry World | December 2011 www.chemistryworld.org upwards of 30 per cent water and 60 per cent energy usage compared to standard processing.’

Eco-bleaching ‘Cotton bleaching with peroxide is carried out at 95°C and a pH of 12 or higher. This was clearly a target for improving the process,’ says Erwin Redling, head of application and screening technology at Huntsman. Genencor and Huntsman have together pioneered a biochemical bleaching process, again relying on enzyme catalysis. The enzyme, an acyltransferase, adds peroxide to a masked acid – for example propylene glycol diacetate – producing the powerful oxidising agent peracetic acid. It is this reagent that breaks the extended conjugated chemical bonding in a chromophore so that it becomes colourless, or else absorbs light outside the visible spectrum. ‘It is possible to reduce energy consumption by almost half due to the considerably lower treatment and rinsing temperatures.

GENENCOR, PART OF DUPONT INDUSTRIAL BIOSCIENCES INDUSTRIAL DUPONT OF PART GENENCOR, No neutralisation is required and at least one or two rinsing baths can considerable environmental the 2-methoxyaniline found by Genencor are working be omitted, reducing water usage.’ and ethical cost (several brands Greenpeace, are banned in Europe.’ towards greener fabric The new process is also gentler on banned sandblasting earlier this processing technologies the fibre. ‘Under normal bleaching year because of the outcry about Greener processing conditions, 9 or 10 per cent of the workers exposed to silica dust). The environmental impact of the fibre is lost. With the gentle bleach ‘In denim only the surface of the textile industry goes beyond the system we only see 4 to 5 per cent warp (the vertical fibres in a final release of toxic materials. ‘The weight loss, and the handle is clearly pair of jeans) is dyed,’ explains industry uses 9 trillion litres of water better,’ says Redling. Bechtold. ‘Mechanical stress annually and 1 trillion kilowatt The textile industry has one of removes the surface leaving a hours of electricity,’ says Scott the most complex supply chains. If fashionable faded appearance.’ Brix, director of global marketing brands or retailers, such as Walmart Some higher-end jeans brands for Genencor’s textiles group. ‘It’s or Marks and Spencers, wish to use cellulase enzymes to break responsible for 10 per cent of the make environmental claims about down the surface of the fibres, world’s carbon impact,’ he adds. the products they sell, they need releasing some of the dye. This Genencor uses bioengineering to to control the environmental cost provides a more environmentally produce novel enzymes for textile at each stage of production. This friendly method to produce a soft, processing steps such as desizing. may be particularly challenging for worn-in appearance. Bechtold ‘Sizing agents such as starch or ‘manufacturers without factories’ proposes applying a paste of NaOH to carboxymethyl cellulose are added that generally design and market – activate the fibre surface before the to protect fibres during the weaving but do not make – their products. ‘A enzyme washing. ‘This enhances the process. Traditionally sizing has couple of years ago brands would enzyme activity in specific areas,’ he been removed with hot water, acid never have dreamed of telling their explains. ‘It can provide the desired or enzymes to solubilise and break manufacturers what to do,’ says pattern of wear while preserving the down the starches into dextrins,’ Brix. ‘They are starting to be more strength of the fabric.’ Brix explains. forceful in asking. They know that Finally, the ‘azo dyes’ and the While enzymatic desizing has they can’t continue to support likely source of 2-methoxyaniline: been practiced for years, it is now producers that may be polluting ‘A significant percentage of dyes also possible to achieve enzymatic or wasting resources without contain azo groups as part of their scouring at the same time, he enraging customers. They generally delocalised structure,’ says Bide. adds. Scouring is done to enhance welcome people like us stopping ‘Azo dyes are generally considered wettability and remove waxes and by to suggest how they can reduce to be non-toxic, some are permitted other impurities. ‘Scouring with ‘The textile their carbon footprint.’ as food colours. The issue which neutral pectate lyase can release industry is has given these materials bad press materials trapped on the cotton responsible Fiona Case is a science writer is the potential cleavage of the azo under the same conditions as based in Vermont, US group and the aromatic amines that desizing enzymes and sometimes for 10 per cent result. The dyes that cleave into even in the same bath, thus saving of the world’s Further reading any of 22 potentially carcinogenic water. Using these specially Greenpeace Dirty Laundry report: aromatic amines, including engineered enzymes can save carbon impact’ http://bit.ly/GPdirtylaundry www.chemistryworld.org Chemistry World | December 2011 | 51