|
|
|
|
| Issue date:01/08/2008 |
| ATA Journal for Asia on Textile & Apparel - Aug 2008 Issue |
| Source:Journal for Asia on Textile & Apparel |
|
by Ian Holme
The textile dyeing industry has been subject to many challenges over the last two decades, but increasingly governments, dyestuff manufacturers, textile dyeing companies, retailers, consumers and water supply companies are actively seeking eco-friendly dyestuffs and processes, which may be defined as those that have a minimal effect upon the ecosystem or the environment.
With the global textile dyestuffs market projected to reach US$5.9 billion by 2010 there is clearly a large scope for the introduction of more eco-friendly dyestuffs and processes.
Reducing impact on earth with bluesign
One measure of the importance of sustainable production and minimizing the environmental, health and safety issues has been the introduction of the bluesign standard from bluesign Technologies AG. Clariant, Huntsman Textile Effects, and now with DyStar Textilfarben GmbH as a new supporter of the bluesign standard, bluesign Technologies AG is now able to offer the ranges of the three largest global manufacturers of textile chemicals and dyestuffs with the highest environmental, health and safety levels and with great knowledge in processes and application technology. DyStar will thus endorse the bluesign standard system as a supporter and will publish their bluesign-compliant products in the bluefinder products database. This database contains the ecologically and economically best available products for the textile industry.
The bluesign standard certifies materials that have been rigorously tested against harmful effects on humans and the environment, as well as optimizing consumption of relevant resources such as water, energy and raw materials. It thus represents a holistic approach to effective management of relevant resources within each single textile process of the supply chain, from fiber production to retail, and from consumer to disposal.
Under its Econfidence programme, DyStar also offers a wide range of dyestuffs and auxiliaries that have been specifically approved for use on organic textiles under the Global Organic Textile Standard (GOTS) as certified by the Institute of Market Ecology (IMO) and Control Union Certifications (CU).
The global market for textile dyestuffs is dominated by the disperse (35%) and reactive (28%) dyestuff ranges, together with acid (12%), direct (7%), vat and indigo (8%), sulphur (6%) and azoic and other dyestuffs (4%) (see table below). The major ecological problems with disperse dyes have been the necessity to eliminate an alkaline reduction clear plus rinsing after exhaust dyeing or pad-dry-thermofix (Thermosol) dyeing of medium-dark depths of color, coupled with up to 10% of the dyestuff left in the dyebath after exhaust dyeing.
Global breakdown of different dyestuff classes *Data above are collated from NSK Srinivasan and A Athalye Colorage 55(3) March (2008) 71, and JR Easton in Color in Dyehouse Effluent and P Cooper (Bradford: Society of Dyers and Colorists) (1995) 9 |
The effluent from the complete scour / dye, alkaline reduction clear, and rinsing stages could potentially contain surfactants, alkali, sodium hydrosulphite, sulphite and sulphate as well as loose dyestuff and dyestuff degradation products.
Dispersing agents can have a significant impact on effluent loading.
The approaches taken by disperse dye manufacturers to minimize ecological problems include:
Development of trichromats with identical / very similar dyeing characteristics;
Use of higher color efficiency dyestuffs;
Introduction of disperse dyes that can be cleared solely with alkali, avoiding the need for a reduction clear requiring sodium dithionite (hydrosulphite);
Development of acidic after clearing -eliminating the need to change the pH and minimizing the number of rinsing baths and chemical load in the effluent.
Production of disperse dyestuffs that have higher color fastness to thermal aftertreatments e.g. benzodifuranone-based disperse dyestuffs;
Elimination of carrier dyeing in favour of high temperature exhaust dyeing.
To meet all ecological requirements, the Dianix disperse dyeing ranges of DyStar do not contain MAK amines generated by reductive cleavage according to EU Directive 2002/61/EEC and German Consumer Goods Ordinance, allergenic disperse dyes (i.e. skin sensitisers) according to Oeko-Tex Standard 100, or restricted polychlorinated aromatic compounds above acceptable trace level. In addition, the products contain heavy metal complex well below the ETAD limit value guideline, and they are also in full compliance with Oeko-Tex Standard 100, according to DyStar.
It is noteworthy that by using Indanthren dyes for the cellulosic portion, which eliminates the need to alkaline reduction clear, it can dye fiber blends in a more ecological way. Processes are applicable for exhaust dyeing and especially for continuous dyeing where eco savings of rinsing, neutralisation and drying are delivered.
Using less water with reactive dyestuffs
Reactive dyestuffs are the major class used to dye bright fashion colors in woven and knitted fabrics as well as on yarn, but it can be seen from the above table that many commodity reactive dyes exhibit low fixation values, necessitating extensive washing off. This is also required to remove hydrolysed reactive dyes.
Homobifunctional reactive dyestuffs, heterobifunctional reactive dyestuffs and now polyfunctional reactive dyestuffs are being produced. Increasing the number of reactive groups can increase the dye fixation to about 90% by pad batch application to cellulosic fibers, largely eliminating the problems experienced with other types of reactive dyes in which the fixation was limited. Because most reactive dyes are highly sulphonated their high aqueous solubility results in less absorption in activated sludge water treatment plants, giving residual color in the final discharged liquor.
New eco-friendly dyes are being developed (Picture source: Clariant) |
Clariant has introduced Drimaren HF-CD reactive dyes for the continuous dyeing of pale shades. Drimaren HF-CD dyes are based upon a trichromat that has been molecularly engineered to produce dyestuffs with the similar affinity factor. This enables Drimaren HF-CD dyes to be applied successfully in pad-dry-chemical pad-steam, and thermofix processes. The trichromat dyestuffs have high fixation values coupled with low to no tailing propensity, and are hence suitable for continuous dyeing processes.
Ensuring reproducibility in cold pad batch, reactive dyeing is an essential feature in producing high quality fabrics using an eco-friendly application technique that minimises water and energy consumption. DyStar has developed its Levafix CA and Remazol RGB reactive dye ranges for all application processes including cold pad batch dyeing of emerised fabrics and have worked closely with Küsters, now a member of Benninger, and other machine manufacturers to optimise laboratory to bulk reproducibility.
This is an important factor as there has been significant growth in the use of cold pad batch dyeing especially for woven cotton-elastomeric blends as well as for knitted fabrics.
DyStar's Controlled Pad Batch system optimises the processing to ensure performance requirements can be achieved. The latest development is a silicate free tropical method using soda ash and caustic soda for the application of Levafix CA, Remazol RGB and Ultra RGB as well as selected Remazol Black dyestuffs. This is a significant advantage for wastewater treatment plant where silicate presents serious problems.
The Remazol Ultra RGB reactive dyes from DyStar can provide deep saturated colors using a trichromat with excellent on-tone build-up as well as shortening the exhaust dye cycle time. A possible reduction in time of up to 30 minutes has been obtained in the migration and alkali addition stage using Remazol Ultra RGB dyes.
Because of the high color strength of the Remazol Ultra RGB dyes, a reduction of up to 50% in dyestuff amount, salt and alkali can be obtained which leads to a significantly decreased impact on effluent discharge and in the total environmental load.
The major problems in vat and sulphur dyeing are associated with the use of sodium dithionite (hydrosulphite) for reduction. Clariant introduced an eco-friendlier Diresul RDT range of sulphur dyestuffs using glucose. DyStar also offers glucose-based reducing agent Sera Con C-SDR for sulphur dyeing for denim.
New indigo dyes for clean denim production
Indigo dyeing is today a niche in the textile production chain but dominant for the fashionable denim articles.
The most important application today is the continuous cotton yarn dyeing on specialized indigo dyeing ranges as rope or slasher types. Current practise is the stock vat preparation of indigo using hydrosulphite as well as the reduction of the indigo by hydrosulphite on the dyeing range followed by five or six air oxidation cycles. In both cases, hydrosulphite has to be used in excess for process safety reasons.
DyStar Indigo Vat 40% Solution is a patented pre-reduced indigo ready for use on the dyeing range. It is synthesized by catalytic hydrogenation, which causes only water as by-product. Due to the specific production process, it is the cleanest technical indigo available. Being sensitive to air oxidation, it has to be handled carefully under nitrogen and fed into the dyeing range with special equipment (Dencon) developed for process optimization from DyStar. The future technology currently in development by DyStar is the electrochemical dyeing process which allows the complete elimination of hydrosulphite.
|
| We are collecting readers' comment for improving our website. If you are willing to help, please CLICK HERE to complete a survey. Your comments matter. |
|
|
|
|
| Copyright © Adsale Publishing Limited. Any party needs to reprint any part of the content should get the written approval from Adsale Publishing Ltd and quote the source "ATA Journal for Asia on Textile & Apparel", Adsale Textile English Website - www.AdsaleATA.com. We reserve the right to take legal action against any party who reprints any part of this article without acknowledgement. For enquiry, please contact Editorial Department. |
|
| Copyright © Adsale Publishing Limited. Any party needs to reprint any part of the content should get the written approval from Adsale Publishing Ltd and quote the source "ATA Journal for Asia on Textile & Apparel", Adsale Textile English Website - www.AdsaleATA.com. We reserve the right to take legal action against any party who reprints any part of this article without acknowledgement. For enquiry, please contact Editorial Department. |
|
|
|
Close
|
|
|
|
|
|
|
The most selected comment of this article is
(2 votes) |
 |
| useful |
|
|
![]() |
| The most selected comment of this article is useful (2 votes) |
|
|
|
|
|
|
 |
|
Write a mail to the editor : 
