Water scarcity and increased environmental awareness are world-wide concerns which are causing a sharp rise in prices for intake and disposal of water. The textiles industry is also one of the biggest consumers of water with conventional textile dyeing using large amounts of fresh water which is disposed of as waste water containing dyestuff chemicals. The Yeh Group says that in its experience, an estimated 100-150 litres of water are needed to process 1 kg of textile material. Water is also used as a solvent in many pre-treatment and finishing processes, such as washing, scouring, bleaching, dyeing, rinsing and finishing and the contaminated water must then be handled and treated prior to disposal or recycling.

DryDye fabrics

The Yeh Group, which produces both warp and weft knitted fabrics, says it will be the first textile manufacturer to implement a new waterless dyeing process developed by DyeCoo Textile Systems of the Netherlands which is currently being readied for commercial introduction in the fourth quarter of this year. The company says it has exclusive rights to the process and is branding fabrics produced using it, as DryDye fabrics. 

Supercritical fluid CO2

Elimination of the water process and chemicals is a real and significant breakthrough for the textile dyeing industry. This new process utilizes supercritical fluid carbon dioxide (CO2) for dyeing textile-materials. It is a completely waterless dyeing process using only nominal amounts of CO2, nearly all of which is recycled. DryDye fabrics dyed with this unique waterless process will have the same dye qualities and durability as current, conventionally-dyed fabrics, a spokesperson for the Yeh Group said.

The Yeh Group, which claims to be an innovative, environmentally responsible producer of quality knit fabrics and garments, supplies to premium brands in sports and intimate apparel markets. By pioneering and implementing this new waterless dyeing process, the company says it will eliminate the use of millions of litres of fresh water in dyeing fabrics using the new process.

Instead of current aqueous dyeing systems, DryDye fabrics will be dyed using supercritical carbon dioxide in a stainless steel chamber developed and tested by DyeCoo. Yeh Group says, for the past three decades, supercritical fluids have been used in various extraction processes, including the extraction of natural substances for the production of pharmaceuticals, cosmetics and spices.  In addition, leading producers of textiles dyestuffs have attempted to harness the technology for textiles dyeing but none has produced a successful commercial system to date.

Supercritical fluid CO2 is said to have become a mainstay in extraction processes in the food industry (decaffeination, extraction of hops) and apparel dry cleaning, where it is said to be the best, gentlest, most thorough cleaning method now available. Carbon dioxide is also said to be considered the best supercritical fluid for the dyeing process, is naturally occurring, chemically inert, physiologically compatible, relatively inexpensive and readily available. 

Dyeing polyester and other synthetics

Using supercritical fluid CO2, polyester and other synthetics can be dyed with modified disperse dyes.  The supercritical fluid CO2 causes the polymer fibre to swell allowing the disperse dye to easily diffuse within the polymer, penetrating the pore and capillary structure of the fibres.  The viscosity of the dye solution is lower, making the circulation of the dye solutions easier and less energy intensive.  This deep penetration provides effective colouration of polymers which are characteristically hydrophobic.  Dyeing and removing excess dye are processes that are done in the same vessel.  Residue dye is minimal and may be extracted and recycled, the Yeh Group says.

Reductions in operating costs

According to the Yeh Group, supercritical CO2 dyeing gives excellent results as far as dye levelness and shade development are concerned. The physical properties of dyed yarns are also said to be equivalent to conventional methods.   Conventional textile dyeing is very water and energy intensive in pre-treatment, dyeing, and post-treatment (drying).  The supercritical CO2 process however, is said to use less energy than conventional processes, resulting in a potential reduction in operating costs of up to 50%. The company says the only overlap is in the pre-treatment process, which is essentially the same for both.

Availability

DryDye fabrics will be available to consumers in early-2011 through selected brand customers of the Yeh Group and the initial brands adopting and marketing DryDye fabrics will be announced in the coming weeks. The Yeh Group was established in 1988 and is located on a 40 acre site near to the city of Bangkok in Thailand where it specializes in performance polyester knit fabrics. The group is composed of Tong Siang and Penn Asia and has sales offices located in Europe and North America. Current customers include Adidas, The North Face, Puma, Mammut, Odlo, Mizuno and Victoria Secret. DyeCoo Textile Systems B.V. is based in the Netherlands and claims to be the world's first supplier of industrial CO2 dyeing equipment, for which it holds patents. The company also offers its own range of dyes for CO2 dyeing.

source:CTEI