Nanotechnology Opens New Routes for the Functional Finishing of Cotton-Rich Textiles

Rapidly emerging nanotechnology offers new and improved ways of imparting a range of functional performance properties to cotton rich fabrics. In fact, textile industry is the first manufacturing industry to come up with finished products that are enhanced through nanotechnology-based functional finishing. To date, textile industry is the only major manufacturing industry that markets a range of end products to the consumers with a nanotechnology label attached to them. This development can be largely attributed to the focused R & D efforts of four or five US-based companies. These companies successfully explored the nanotechnology route to impart stain resistance, flame retardancy, wrinkle resistance, moisture management, and other enhancements associated with antimicrobial, UV protection, and soil release properties.

Nano-Care technology for water-repellent and stain-resistant cotton fabrics:

Greensboro, N.C.-based Galey & Lord Inc. is using new cutting-edge technology to give its cotton fabrics permanent water repellence and stain and wrinkle resistance. The fabric manufacturer has recently been licensed to use technology developed by Nano-Tex LLC, in its fabrics for the bottomswear market.

Through Nano-Texs Nano-Care technology for cotton, nano-whiskers 1/1000 the size of a typical cotton fiber are attached to the individual fibers. The changes to the fibers are undetectable and do not affect the natural hand and breathability of the fabric. The whiskers cause liquids to roll off the fabric. Semi-solids such as ketchup or salad dressing sit on the surface, are easily lifted off and cause minimal staining, which should be removed with laundering.

The attributes provided by Nano-Care have traditionally been added by the use of coatings, which affect the fabrics inherent qualities, or by other treatments that eventually wash or fade away. While Nano-Care provides the above attributes, it also allows moisture to pass through the fabric.

Nano-Pel Technology for durable water-and-oil repellent finishing:

This nanotech application of water-and-oil repellent finishing is effective for use in natural fibers such as cotton, linen, wool and silk, as well as synthetics such as polyester and nylon. Unsurpassed performance in durability and water and oil repellency is claimed, particularly with natural fibers. Nano-Pel cotton has been shown to withstand 50 home launderings, with functionality maintained for water and oil repellency (80 and 4) even after 20 washes. Heat treatment, such as through ironing or tumble drying, is required for the onset of water-and-oil repellency. Nano-Pel application in commercial production in the US has so far been extended to the area of interior furnishings, ticking (bed mattresses) and home clothing (aprons etc.).

Nano-Touch to give cotton-like touch to synthetics:

This finishing technology gives durable cellulose wrapping over synthetic fiber. Cellulosic sheath and synthetic core together form a concentric structure to bring overall solutions to the disadvantages of synthetics being hydrophobic, electrostatic, having artificial hand and glaring luster. It is claimed to last for 50 home launderings. Nano-Touch can also be expected to increase the appeal for synthetic micro fiber fabrics such as, crepe de Chine, faille, koshibo, charmeuse, chiffon and georgette.

Nano-Press to impart durable dimensional stability to 100% cotton:

One of the short comings of conventional shape memory dimension-stabilizing finishes is their limited applicability to 100% cotton. Deterioration in post-treatment strengths, especially that in the tensile strength of weft yarn being as high as 35 to 60%, makes application ill-suited for commonly-used thin woven fabrics. The Nano-Press durable dimension-stabilizing finish can solve this problem. Nano-Press is claimed to maintain approximately the same tensile strength of weft and warp yarns as that of the original. It is also claimed that the biggest drawback of conventional methods, rapid wear of the hems of cotton trousers due to poor flex abrasion resistance, can be reversed and enhanced to as much as seven times of that of the untreated. Nano-Press appears revolutionary in that it enables dimension stabilization of thin cotton fabrics without the need to sacrifice strength and durability.

Self-cleaning clothes may be the norm very soon:

Self-cleaning clothes in future may make washing a thing of the past, and researchers have indeed invented an efficient way to coat cotton cloth with tiny particles of titanium dioxide.

These nano particles are catalysts that help to break down carbon-based molecules, and require only sunlight to trigger the reaction. The inventors, Nature magazine says, believe that these fabrics could be made into self-cleaning clothes that tackle dirt, environmental pollutants and harmful microorganisms. They may wear out but would never become dirty so long sunlight is available.

The titanium dioxide particles covering the cloth are just 20 nano meters across, about 2,500 times smaller than the width of a human hair. The researchers' key breakthrough was to ensure that these particles had exactly the right arrangement of atoms, called an 'anatase' crystal structure, which has been difficult to achieve in the past in such tiny grains. This arrangement boosts the particles' catalytic power, Nature says.

The researchers, Walid Daoud and John Xin from the Hong Kong Polytechnic University, Kowloon, dipped cotton patches into a liquid slurry of titanium dioxide for just half a minute before removing them, padding them dry, and heating them to 97 degree C in an oven for 15 minutes. Three hours in boiling water completed the coating process, which they describe in the Journal of the American Ceramic Society.

"Titanium dioxide, in the presence of ultraviolet light, will oxidize a wide range of organic materials," explains Bob Skelton, a chemical engineer from Cambridge University, Britain. When light hits the catalyst it frees up electrons within the crystal and these react with oxygen from the air. This generates free-radical oxygen, a powerful oxidizing agent that can break down grime into smaller particles such as carbon dioxide and water. Because the catalyst does not get used up, it can keep on working as long as it is exposed to sunlight.

Self-cleaning materials are particularly popular in the Far East, and a quarter of all toilet bowls coming on to the market in Taiwan, for example, now come with self-cleaning nano-coatings, Nature says.

Flame Retardant Nano-Particles for Textiles:

Nyacol Nano Technologies, Inc. offers colloidal antimony pentoxide as a fine particle dispersion for use as a flame-retardant synergist with halogenated flame-retardants. The dispersions offer many advantages over conventional antimony trioxide systems:

Colloidal dispersions will not settle out.
Spray guns are not clogged.
Nyacol's products can be used in clear coat applications.
The negative effect on deep colors is reduced.
The products can be easily mixed and sprayed.

Colloidal antimony pentoxide is offered as water dispersions, organic dispersions, powder and polymer concentrates. The choice of product will depend on the application and desired properties.

Nanotechnology holds a very promising future for textiles. It is estimated that it will bring about hundreds of billions of market impact on new materials within a decade; textiles certainly have an important share in this material market

References:

1. Lei Quan, Nanotechnology in Textiles: Recent Developments and Future Prospects, AATCC Review, May 2004
2. Wood, Andrew, Chemical Week, October 16, 2002, p17-21.
3. http://www.nanophase.com/applications
4. Textile Horizons, Nanotechnology and the Shrinking World of Textiles, Sep-Oct 2001.

About the author:

RAHDHAKRISHNAIAH PARACHURU

RAHDHAKRISHNAIAH PARACHURU is a Senior Research Scientist with Georgia Institute of Technology, Atlanta. He has doen is B.Tech and M.Tech from University of Madras, Ph.D from IIT Delhi and MS with a major in Applied Statistics from Georgia State University, Atlanta.

He has a vast professional experience and has worked with renowned institutes in India, Raleigh and Atlanta. A member of Fiber Society, AATCC, ASME Division of Textile Engineering, TQCA and the Indian Textile Association, Rahdhakrishnaiah Parachuru has received many Honors and Awards like merit scholarship for undergraduate study in Textile Technology at the University of Madras, India, Award from the state of Tamilnadu, India for advising the best graduate-student project of the year in Textile Technology and award from the National Textile Center for submitting the best research proposal in the textile fabrication area. He has been honored as the Approved Ph. D. thesis examiner of the IIT, Anna University, Calcutta University and Bharathiar University and Official research reviewer of the Textile Research Journal, Journal of Textile Association, and Indian Journal of Fibre & Textile Research.