1 Functional Nano Finishes For Textiles By: D. Gopalakrishnan & K.G. Mythili 2 Functional Nano Finishes For Textiles By: D. Gopalakrishnan & K.G. Mythili Sardar Vallabhbhai Patel Institute of Textile Management, 1483, Avinashi road, Peelamedu, Coimbatore – 641 004 Department of Textile technology, PSG College of Technology, Peelamedu, Coimbatore – 641 004 Nanotechnology is all about making products from very small constituents, components or subsystems to gain greatly enhanced material properties and functionality. One area where innovation is proceeding at a very fast pace is miniaturization. High levels of miniaturization is achieved by the emerging field of nano technology ability to work in the molecular level atom by atom, to create a large structures with fundamentally new properties and functionalities, with nano finishing. The unique and new properties of nano material have attracted not only scientists and researchers but also businesses, due to their huge economical potential. Nanotechnology also has real commercial potential for the textile industry. The use of nanotechnology in the textile industry has increased rapidly due to its unique and valuable properties. The future of technology at times becomes easier to predict. Computer will Compute faster, materials will become stronger, the technology that works on the nanometer scale. The molecules and atoms will be large part of this future, enabling the textile field of human presence. It is raising wave in textile to get a product which is having high quality and precision. Nanotechnology is much discussed these days as an emerging frontier –a real in which machines operate at a scale of billionths of a meter. It is a multitude of rapidly emerging technologies, based upon the scaling down of existing technologies to the next level of precision and miniaturization. Nano finishing is concerned with positive control and processing technologies in the sub nano meter range and so must play an essential role in the fabrication of extremely precise and fine parts. The Nano technology has laid its imprints in all the fields of science and engineering. The present status of nanotechnology use in textiles is reviewed, with an emphasis on improving various properties of textiles. 1. Introduction Nanotechnology is defined as “The precise manipulation of individual atoms and molecules to create layer”. One nanometer is one billionth of a meter. Nanotechnology according to the National Nanotechnology Initiative (NNI) is defined as utilization of structures with at least one dimension of nanometer size for the construction of nano materials, devices or systems with novel or significantly improved properties due to their nano size. Nano finishing means any technology done on a nanometer or (10⎯9) meter scale. The main aim of the nano finishing is “the precise manipulation of an individual atoms and molecules to create a structure. This technology was launched 40 years ago by Richard Feynmanand. Then next milestone was achieved by publishing K. Eric Drexler’s definite book about nanotechnology. The nano technology was adapted to textile in 1998 by Dr. David Soane. It is applicable in producing nanofibres, color changeable cloths, anti-stain, anti-wrinkle and some other finishing processes and also in filter fabrics. The development of ultra fine fibers, functional finishes and smart textiles based on the nano technology has end less properties and their functional properties are more superior than the conventional process due to their higher surface area to volume ratio with their nano finishing. NANO is not a single technology, but a million different things. And its unique feature is that there is some thing small about it with its finishing .It would be appropriate to say that “The Next Big Thing Is Really small”. as Nano technology as a whole is still in relatively early stage of development, it is attracting lots of research work and it would not be hyperbole to state “Tiny particles are going to shape our future with its next generation finishing like (nano –care , nano-pel , nano- touch , nano-dry, nano-sphere) 3 1.1. The Definition Nanotechnology is the study and design of systems at the nanometre scale [0.000000001 (10 -9 ) metre] the scale of atoms and molecules. Nanoscale materials can be rationally designed to exhibit novel and significantly improved physical, chemical and biological properties, because of their size. Nonwoven fabrics composed of electro spun nanofibres have a large specific surface area, a high porosity and a small pore size in comparison with commercial textiles making them excellent candidates for use in filtration, medical and membrane applications. Nowadays, polymer nanofibres are used in various applications. 2. Water Repellence 2.1 Easy Care-Hydrophobic Nano Finish Hydrophobic surfaces can be produced mainly in two ways (i) by creating a rough structure on a hydrophobic surface (ii)by modifying a rough surface using material with low surface free energy. Both the approach have been used to give a hydrophobic finish to textile substrates. Figure.1. Easy care-Hydrophobic Nano Finish The water-repellent property of fabric by creating nano-whiskers, which are fluorocarbons and 1/1000 of the size of a typical cotton fibre, that are added to the fabric to create a peach fuzz effect without lowering the strength of cotton. Thus a rough hydrophobic layer is formed. Fluorocarbons are a class of organic chemicals that contains perfluroalkyl residue in which hydrogen atom have been replaced by Fluorine. These chemicals have very high thermal stability and low reactivity. 2.2 Super Hydrophobicity Hydrophobic fluorocarbon finishes as stated above lower the surface energy and can give a maximum water contact angle of roughly 120.To get higher contact angle and to have self- cleaning ability, super-hydrophobic finish with a contact angle of above 160 is required. This type of finish can not be obtained by surface coating. Super hydrophobic increase in surface roughness provides a large geometric area for a relatively smack projected area. The roughened surface generally Figure. 2. Super-Hydrophobic Finish 4 takes the form of a substrate member with a multiplicity of micro scale to Nanoscale projections or cavities. Water Repellency of rough surface was due to the air enclosed between the gaps in the surface. This enlarges the air /water interface while the solid/water interface is minimized. In this situation, spreading does not occur the water form a spherical droplet . 2.3 Self Cleaning Effect The self cleaning property of plant leaves rough surface was investigated .About 340 plant species were investigated ,majority of wettable leaves investigated were more or less smooth without any prominent surface sculptures (θ<110).In contrast water-repellent leaves exhibit various surface sculptures mainly epicuticular wax crystal in combination with papillose epidermal cells.Their θ >160.They observed that on water-repellent surface water concentrated to form spherical droplets.It came of the leaf very quickly even at slight angle of inclination (<5) out leaving any residue . Figure.3. Typical Float Glass Surface θ°~ 30°, Smooth Silane Treated Glass Surface θ ~ 110°, Super Hydrophobic Structured Surface θ > 160° Particles of all kind adhering to leaf surface were entirely removed from leaf when subjected to natural or artificial rain. The dirt deposited on the waxy surface of the leaves are generally larger than the microstructure of the surface of the leaf and are hence deposited on the tips, as a result the interfacial area between both is minimized. In this case of a water droplet rolling over a particle, the surface area of the drop exposed to air is reduced and energy though absorption is gained .Since the adhering between particle and water droplet ,the particle is captured by the water drop and removed from the leaf surface. This effect is known as lotus effect (fig.4).The lotus effect depends on two factors namely super hydrophobicity and very high water contact angle and a very low roll off angle. Figure.4. Lotus effect Nano-Tex, the Swiss-based textile company Schoeller developed the Nano Sphere to make water-repellent fabrics. Nano Sphere impregnation involves a three-dimensional surface structure with gel-forming additives which repel water and prevent dirt particles from attaching themselves. The mechanism is similar to the lotus effect occurring in nature, as demonstrated in Figure 3. Lotus plants have super hydrophobic surfaces which are rough and textured. Once water droplets fall onto them, water droplets bead up and, if the surface slopes slightly, will roll off. As a result, the surfaces stay dry even during a heavy shower. Furthermore, the droplets pick up small particles of dirt as they roll, and so the leaves of the lotus plant keep clean even during light rain. 5 Figure.5. Mechanism of Nano Sphere on textiles applied by NanoSphere technology (a) Water droplet rolls down a plant, (b) Water droplet rolls down a lotus plant 3. UV-protection Previously organic and in organic UV absorbers were coated on the textile material they prevent UV radiation effectively but they are less durable. UV blockers are usually certain semiconductor oxides such as TiO 2 , ZnO, SiO 2 and Al 2 O 3 . Among these semiconductor oxides, titanium dioxide (TiO 2 ) and zinc oxide (ZnO) are commonly used. It was determined that nano-sized titanium dioxide and zinc oxide were more efficient at absorbing and scattering UV radiation than the conventional size and were thus better able to block UV . This is due to the fact that nano-particles have a larger surface area per unit mass and volume than the conventional materials, leading to the increase of the effectiveness of blocking UV radiation. For small particles, light scattering predominates at approximately one- tenth of the wavelength of the scattered light. Raleigh’s scattering theory stated that the scattering was strongly dependent upon the wavelength, where the scattering was inversely proportional to the wavelength to the fourth power. This theory predicts that in order to scatter UV radiation between 200 and 400 nm, the optimum particle size will be between 20 and 40 nm. UV-blocking treatment for cotton fabrics was developed using the sol-gel method. A thin layer of titanium dioxide is formed on the surface of the treated cotton fabric which provides excellent UV-protection; the effect can be maintained after 50 home launderings. Apart from water droplet rolls titanium dioxide, zinc oxide nanorods of 10 to 50 nm in length were applied to cotton fabric to provide UV protection. According to the study of the UV-blocking effect, the fabric treated with zinc oxide nanorods demonstrated an excellent UV protective factor (UPF) rating. (a) (b) Figure.6. (a) Normal fiber (b) Fiber treated with Tio 2 6 (1) (2) Figure.7. (1) Conventional Sunscreen with Micronized ZnO (2) Sunscreen with ZnO Nano powder 4. Anti-Bacteria Neither natural nor synthetic textile fibers are resistant to bacterial or pathogenic fungi. Therefore, antibacterial disinfection and finishing techniques have been developed for many types of textiles including treatment of textile fibers by padding cotton and polyester fabrics with nano-sized silver, titanium dioxide and zinc oxide colloidal solutions (25-50 ppm). Metallic ions and metallic compounds display a certain degree of sterilizing effect. It is considered that part of the oxygen in the air or water is turned into active oxygen by means of photo catalysis with the metallic ion, thereby dissolving the organic substance to create a sterilizing effect. With the use of nano-sized particles, the number of particles per unit area is increased, and thus anti-bacterial effects can be maximized. Nano-silver particles have an extremely large relative surface area, thus increasing their contact with bacteria or fungi, and vastly improving their bactericidal and fungicidal effectiveness. Nano-silver is very reactive with proteins. When contacting bacteria and fungus, it will adversely affect cellular metabolism and inhibit cell growth. It also suppresses respiration, the basal metabolism of the electron transfer system, and the transport of the substrate into the microbial cell membrane. Furthermore, it inhibits the multiplication and growth of those bacteria and fungi which cause infection, odour, itchiness and sores. Hence, nano-silver particles are widely applied to socks in order to prohibit the growth of bacteria. In addition, nano-silver can be applied to a range of other healthcare products such as dressings for burns, scald, skin donor and recipient sites. Figure.9. Action of Microbes before & after finishing 7 Nano-Tex™ Resists Spills Fabric Protection Repel Ink Inks and dyes contain concentrated amounts of quick-drying colorants. Fabrics treated with NANO-TEX Resists Spills protection are not protected from these types of colorants but if lifted quickly, stains can be minimized. Figure.10. Nano-Tex™ Resists Spills Fabric Protection Resist Mud Stains NANO-TEX Resists Spills fabric protection protects against both water-based and oil-based liquids. Resists Spills fabric protection offers superior liquid repellency, which helps to minimize stains. If the mud is sitting on the surface of the fabric, NANO-TEX fabric protection will allow the wearer to carefully lift off the mud, therefore minimize staining. If the mud has been ground into the NANO-TEX Resists Spills enhanced fabric, recommended garment care cleaning tips should be followed to minimize or prevent the potential for staining. Mud stains or thick oils that are smeared onto fabric may leave some residual staining. 5. Photocatalysis When a semiconductor material is illuminated with ultra band gap light it becomes a powerful redoxcatalyst capable of killing bacteria, cleaning water, and even splitting water to give hydrogen and oxygen 5.2 Photocatalysis Reaction i).Partial reactions hv (UV) Ti0 2 e- + p (Exiton) H0+p H0 Ti 4 Ti 3 Ti 3 [ Ti 4 O 2 abs] [Ti 4 O 2 abs] + H 2 0 Ti 4 + H0 + H0 2 ii).Overall reaction H 2 0 + O 2 hv HO + HO TiO Titanium dioxide is a photo catalyst, once it is illuminated by light with energy higher than its band gaps, the electrons in TiO 2 will jump from the valence band to the conduction band and the electron (e-) and electric hole (h+) pairs will form on the surface of the photocatalyst. The negative electrons and oxygen will combine into O 2 - the positive electric holes and water will generate hydroxyl radicals. Since both are unstable chemical substances, when the organic compound falls on the surface of the photocatalyst it will combine with O 2 - and OH- respectively, and turn into carbon dioxide (CO 2 ) and water (H 2 O). 8 Through the reaction, the photocatalyst is able to decompose common organic matters in the air such as odour molecules, bacteria and viruses. It was determined that a fabric treated with nano-TiO 2 could provide effective protection against bacteria and the discoloration of stains, due to the photocatalytic activity of nano-TiO 2 . On the other hand, zinc oxide is also a photocatalyst, and the photocatalysis mechanism is similar to that of titanium dioxide; only the band gap is different from titanium dioxide. Nano-ZnO provides effective photocatalytic properties once it is illuminated by light, and so it is employed to impart anti- bacterial properties to textiles. 6. Next Generation Finishing 6.1. Nano-Care A technology that brings about an entirely carefree fabric with wrinkle resistant, shrink proof, water and stain repellent properties, intended for use in cellulosic fibers such as cotton and linen. It is a next-generation, ease-of-care, dimension-stabilizing finish, one step ahead of methods that simply give wrinkle resistance and shrink-proofing. Nano-Care withstands more than 50 home launderings. It imparts water repellency and stain resistance superior to those of conventional methods, maintaining high water and oil repellency levels (80 and 4) even after 20 home washes. Features • Superior Stain, Water and Oil Repellency • Resists Wrinkles • Breathable Fabric • Preserves Original Hand • Easy Care 6.2. Nano-Pel 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, nylon and acryl. Unsurpassed performance in durability and water and oil repellency may be expected particularly with natural fibers. Nano-Pel cotton withstands 50 home launderings, with functionality levels well-maintained for water and oil repellency (80 and 4) even after 20 washes (Figure shows Before & After). 9 Features Superior Water and Oil Repellency • Minimize Stains • Breathable Fabric • Preserves Original Hand • Easy Care • Durable Performance 6.3. Nano-Dry It is a hydrophilic finishing technology that imparts outstanding endurance of more than 50 home launderings and offers prospects of considerable contribution to the area of polyester and nylon synthetic garments. Nano-Dry exerts durability superior to that of the hydrophilic finishing of polyester commonly carried out in Japan using polyethylene glycol polymer molecules, and allows no dye migration when deep-dyed. It is expected to serve particularly well for use in nylon, as there exists no such durable hydrophilic finishing, in the field of sportswear and underwear that require perspiration absorbency. Considerable growth is expected within the forthcoming period of 3 to 6 months, mainly in the field of sportswear. Features • Moisture Wicking • Retains Breathability of Fabric • Quick Drying • Preserves Original Hand • Durable Performance 6.4. Nano-Touch This ultimate 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 will broaden the existing use of synthetics, being free of their disadvantages as found in synthetic suits being hydrophobic, electrostatic and having unnatural hand. The following are examples of new areas of use created through Nano- Touch, a new standard for fiber compounding. Self-assembled nanolayer (SAN) coating is a challenge to traditional textile coating. Research in this area is still in embryo stage. In self- assembled nanolayer (SAN) coating, target chemical molecules form a layer of thickness less than nanometer on the surface of textile materials. Additional layers can be added on the top of the existing ones creating a nanolayered structure. Different SAN approaches are being explored to confer special functions to textile materials. 10 Features • Superior Refinement in a Blended Fabric • Durable Performance • Luxurious Cotton-Like Hand • Easy Care • Reduced Static Build-up 7. Future Prospect The development of ultra fine fibers, functional finishes and smart textiles based on the nanotechnology has end less properties. At present, the application of nano technology in textiles has merely reaches only the starting line. The reason for less commercialization of nano technology is due to their higher time consumption and cost factor involved. The current global market for Nanoscale technologies is estimated at around US $ 45 billions and is going to grow to US $ 1 trillion by 2015. The world leaders in this technology area are United States, Japan, and Europe. Ashima and Arvind are the first two Indian textile companies to have bought license to produce nanotechnology driven cloths. Future developments of nanotechnologies in textiles will have a two fold focus: (a) Upgrading existing functions and performances of textile materials; (b) Developing multifunctional finishes using nano technology The new functions with textiles to be developed include,  Nanofibres that would detoxify and filter toxic chemicals, warfare agents. Multiple and sophisticated protection and detection.  health-care and wound healing functions Conclusion Nano finishes being developed for textile substrates are at their infantile stage. Nanotechnology is an emerging technology, which is no longer just a vision for the future as it was generally seen at the end of 20th century. Instead, nanotechnology is a ubiquitous technology with a lot of potential to impact on every aspect of modern technology. Nanotechnology, with all its challenges and opportunities, is an unavoidable part of our future. The possibilities with nanotechnology are immense and numerous .The researches are filled with technology are beginning to make their mark. The extent to which nanotechnology will impact our lives only depends on the limits of human in genuinity. It can rightly be said that nanotechnology is slowly but steadily ushering in the next industrial revolution. Undoubtedly, Nanotechnology holds an enormously promising future for textiles. It is estimated that nanotechnology will bring about hundreds of billions dollars of market impact on new materials within a decade to textile certainly. The new concepts exploited for the development of nano finishes have opened up exciting opportunities for further R&D. In future, one can expect to see many more developments in textiles based on nano technology. At last “Nano-Finishing” can be described as a “Synonyms for Innovation”. Reference 1. Russell, E., Nanotechnologies and the shrinking world of textiles, Textile Horizons, 2002. 9/10: p.7-9. 2. Cramer, Dean, R., Ponomarenko, Anatolyevna E., Laurent, S., and Burckett, J.C.T.R., Method of applying nanoparticles, U.S. Pat. No: 6,645,569, 2003 3. Anonymous, Small-scale technology with the promise of big rewards, Technical Textiles International, 2003. 3: p. 13-15. 4. Xin, J.H., Daoud, W.A., and Kong, Y.Y., A New Approach to UV-Blocking Treatment for Cotton Fabrics, Textile Research Journal, 2004. 74: p. 97-100. [...]... Preparation of nanocomposite fibers for permanent antibacterial effect, Journal of Materials Science, 2003 38: p 2143-2147 6 Draper D., Very little to it, World Sports Activewear, 2003 19: p 16-17 7 Mills Andrew & Lee Soo-Keun, J - (Photochem Photobiol Chemistry), 2002 8 Holme I, - (Textile Finishing), 2003 9 Derek Heywood - (Society of Dyers and Colourists, England) 2003 http://www .nano. org.uk/nanocomposites_review.pdf... international confrences in all over india and i participated in various technical workshops & innovative project works I published several articles in journals,magazines Area of Interest: innovative textiles, Technical textiles Coimbatore-641 004, Email dgk_psgtech@yahoo.co.in To read more articles on Textile, Fashion, Apparel, Technology, Retail and General please visit www.fibre2fashion.com/industry-article... (Photochem Photobiol Chemistry), 2002 8 Holme I, - (Textile Finishing), 2003 9 Derek Heywood - (Society of Dyers and Colourists, England) 2003 http://www .nano. org.uk/nanocomposites_review.pdf http://www .nano- tex.com/Flash/Products/Products http://www.ncsu.edu/research About the author: K.G Mythili - Department of Textile technology, PSG College of Technology, Peelamedu, Coimbatore – 641 004 Gopalakrishnan . Functional Nano Finishes For Textiles By: D. Gopalakrishnan & K.G. Mythili 2 Functional Nano Finishes For Textiles By: D. Gopalakrishnan. generation finishing like (nano –care , nano- pel , nano- touch , nano- dry, nano- sphere) 3 1.1. The Definition Nanotechnology is the study and design of systems at the nanometre scale [0.000000001. development of ultra fine fibers, functional finishes and smart textiles based on the nanotechnology has end less properties. At present, the application of nano technology in textiles has merely reaches