The impact of nanotechnology in the arena of textile apparel finishing has brought up innovative finishes along with new application techniques. These advanced apparels finishes setup an unprecedented level of textile performances of strain-resistant, hydrophilic, antistatic, wrinkle resistant, shrink proof abilities and protection methods. Coating the surface of textiles and clothing with nanoparticles is an approach to the production of highly active surfaces to have UV-blocking, antimicrobial, flame retardant, water repellant and self-cleaning properties. As there are various potential applications of nanotechnology in the textile industry, only some of the well-known properties imparted by nano-treatment are critically discussed in this article.
Keywords: Nanoparticles, water repellency, antibacterial, photocatalyst, etc.
Nanotechnology is an emerging interdisciplinary technology that has been booming in many areas during the recent decade. Its profound societal impact has been considered as the huge momentum to user in a second industrial revolution. The concept of nanotechnology has been started about for the last half century ago and it has already been established it’s potentiality in the textile applications. The use of nanotechnology in textile industry has increased rapidly due to its unique properties of applications. The present status of nanotechnology which is using in textile industry is reviewed, with an emphasis on improving the properties of textile materials. Due to immense economical potentiality and unique properties of nanomaterials, nanotechnology has attracted both the economical and scientists concern. Nanotechnology is increasingly attracting worldwide attention, because it is widely perceived as offering huge potential in worldwide range of end uses. Applications of nanomaterials in textile are expected to increase by a trillion dollar in industry sector by the next decade for their tremendous technological, economical and ecological benefits. Research involving nanotechnology to improve performances or to create unprecedented functions of textile materials is flourishing. In this article we have focused on the applications of nanosized substances to generate advanced quality during the manufacturing and finishing processes in textile.
Nanotechnology Applications in Textiles:
Due to the advancement of nanotechnology in the manufacturing of fibers/yarns including the development of fabric finishes, the applications and scopes are widespread in the area of textiles for the last few decades. The recent advancement of fabric finishes is greatly contributed to the advancement in the area of nanotechnology1. By combining the nanoparticles with the organic and inorganic compounds, the surfaces of the fabrics treated with abrasion resistant, water repellent, ultraviolet (UV), electromagnetic and infrared protection finishes can be appreciably modified. In the most recent age, Titanium-dioxide (TiO2) nanoparticles have been utilized for the UV protection. The usage of nanoengineered cross-link agents during finishing process enhances the wrinkle resistance of cotton fabrics. The newly developed micro encapsulation technique is being used in textile industry for flame or fire retardant agents. Microcapsules using siIver nanoparticles (Silver Cap) have been developed for providing anti-microbial effects and for odor control2.
The water repellant property of fabrics is obtained by creating combination of micro and nano-whiskers with low surface energy, which are generated by wax crystals in the range of size 10-3 for a typical cotton fibre, which are added to the fabric to create a peach fuzz effect. This facilitates like a cushion of air on the fabric surface without lowering the strength of fabric. When water hits on the surface of the fabric, it beads on the points of the whiskers, the beads compress the air in the cavities between the whiskers creating extra resistance. In technical terms, the fabric has been rendered super-non wettable or super-hydrophobic (Figure 2). The whiskers also create fewer points of contact for dirt. When water is applied to soiled fabric, the dirt adheres to the water far better than it adheres to the textile surface and is carried off with the water as it beads up and rolls off the surface of the fabric. This is the similar concept how the “Soil-cleaning” performed on the leaves of the lotus plant (Figure 3(A),(B)).
The realization of self-cleaning properties on textile surfaces by using the nanotechnology includes a vast potential for the development of new materials or new products and applications for known materials. Self-cleaning garments have been developed, keeping nature as a role model considering self-cleaning property of plant leaves and insects (Figure 3(A),(C)). Majority of wettable leaves and insects are naturally more or less smooth without any prominent changing of surface morphology. In contrast water repellant leaves and insects exhibit various surface sculptures mainly epicuticular wax crystal in combination with papillose epidermal cell. The opening of new application fields for textiles will lead to a new growth stage. For the growing market of technical textiles a further increase in production volume, sales and application fields can be expected by successful transfer of the self-cleaning effect on textile materials. Structure based soil and water-repellent properties lead to an efficient use of materials and are therefore in agreement with the principles of sustainable development. The use of a self-cleaning coating is attractive as well as are labor saving and effectively improve the appearance of the environment. In the long run, it can save time and money by reducing expensive dry cleaning bills. It could take several years for the retail market of self-cleaning clothes and linens to launch as the technology still needs modification.
Figure 3: Examples of self-cleaning surfaces in nature.
German researchers discovered that the lotus plant, admired for the resplendence of its flowers and leaves, owed this property of self-cleaning to the high density of minute surface protrusions. These protrusions catch deposits of soil preventing them from sticking. When it rains, the leaf has a hydrophobic reaction. Water rolls around as droplets, removing dust as it moves (Figure 3 (B)).
Nanotechnology in Textile finishing:
The impact of nanotechnology in the textile finishing area has brought up innovative finishes as well as new application technique. Particular attention has been paid in the application of chemical finishing by nanomaterials in textile. More efficiently, discrete molecules or nanoparticles of finishes can be brought individually to designated sites on textile materials in a specific orientation and trajectory through thermodynamic, electrostatic or other technical approaches (Figure 4).
Nanoparticles such as metal oxides and ceramics are also used in textile finishing altering surface properties and imparting textile functions. Because of nanosize particles are transparent, and do not blur color and brightness of the textile substrates, preventing nanoparticles from aggregation which is the key to achieve a desired performance. The fabrics which were treated with TiO2 and MgO nanoparticles previously is replaced with active carbons that are used as chemical and biological protective materials. The photocatalytic activity of TiO2 and MgO nanoparticles can break harmful and toxic chemicals and biological agents. These nanoparticles can be pre- engineered to adhere to textile substrates by using spray coating or electroplating methods. Finishing with nanoparticles can convert fabrics into sensor-based materials. If nanocrystalline piezoceramic particles are incorporated into fabrics, the finished fabric can convert exerted mechanical forces into electrical signals enabling the monitoring of bodily functions such as heart rhythm and pulse if they are worn next to skin.
The most important functions performed by the garment are to protect the wearer from the weather. However it is also to protect the wearer from harmful rays of the sun. The UV-blocking property of a fabric is enhanced when a dye, pigment, de-lustrant, or ultraviolet absorber finish is present that absorbs ultraviolet radiation3 and blocks its transmission through a fabric to the skin. To impart UV- protection, several nanocompounds or nanoparticles can be applied on textile material. I
norganic uv-blockers are more preferable to organic UV-blockers as they are non-toxic and chemically stable under exposure to both high temperatures and UV. Inorganic UV-blockers are usually certain semiconductor oxides such as TiO2, ZnO, SiO2 and Al2O3. Among these semiconductor oxides, titanium dioxide (TiO2) and zinc oxide (ZnO) (Figure 4) 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. Various research works on the application of UV-blocking treatment to fabric using nanotechnology were conducted. 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. Fabric treated with zinc oxide nanorods demonstrates an excellent UV-protective factor (UPF) rating.
Figure 5: Fabric coated with ZnO nanomaterials for UV-protected clothing (SEM-image).
Fabric treated with UV-absorbers, ensures that the clothes deflect the harmful UV- rays of the sun, reducing a person’s Ultra Violet Rays exposure and protecting the skin from potential damage (Figure 5). The extent of skin protection required by different types of human skin depends on UV-radiation intensity & distribution in reference to geographical location, time of day, and season4. This protection is expressed as UPF, higher the UPF value better is the protection against UV-radiation. Titanium dioxide is a photocatalyst; once it is illuminated by light with energy higher than its band gaps, the electrons in TiO2 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 O2 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 O2 and OH- respectively, and turn into carbon dioxide (CO2) and water (H2O). This reaction is called ‘oxidation-reduction’, and the mechanism is shown in Figure 6.
Several investigations have been carried out on the basis of the use of the photocatalytic property of TiO2, in the field of textiles5. On other hand, ZnO is also a photocatalyst, and the photocatalysis mechanism is similar to that of TiO2; only the band gap (ZnO: 3.37eV, TiO2: 3.2eV) is different from titanium dioxide.
For imparting anti-bacterial properties, nano-sized silver, titanium dioxide and zinc oxide have been used so far. 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 catalysis with the metallic ion, thereby dissolving the organic substance to create a sterilizing effect6. With the use of nano-sized particles, the number of particles per unit area is increased, and thus anti-bacterial effects can be maximized (Figure 7). Nanosilver 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, nanosilver particles are widely applied to socks in order to prohibit the growth of bacteria.
Figure 7: Silver based nanoparticles representing a) structural view of a silver nanoparticle containing functional microcapsule; b) cross-section of fiber coated with silver nanoparticle.
In addition, nano-siIver can be applied to a large range of other healthcare products such as dressings for burns, scald, skin donor and recipient sites. Through the reaction, the photocatalyst is able to decompose common organic matters in the air such as odour molecules, bacteria and viruses. It has been established that a fabric treated with nano-TiO2, could provide effective protection against bacteria and the discoloration of stains, due to the photocatalytic activity of nano-TiO2. ZnO nanoparticle can also provide effective photocatalytic properties once it is illuminated by light, by the way it can be employed to impart anti-bacterial properties to textiles.
Static charge usually builds up in synthetic fibres such as polyamide and polyester because they absorb little water. Cellulosic fibres have higher moisture content to carry away static charges, so that no static charge will accumulate. As synthetic fibers provide poor anti-static properties, research work concerning the improvement of the anti-static properties of textiles by using nanotechnology were conducted. TiO2, ZnO and nano antimony-doped tin oxide (ATO) provide anti-static effects because they are electrically conductive materials. Such material helps to effectively dissipate the static charge which is accumulated on the fabric. On the other hand, silane nanosol improves anti-static properties, as the silane gel particles on fibre absorb water and moisture in the air by amino and hydroxyl groups and bound water. Nanotechnology has been applied in manufacturing an anti-static garment1, 5, 6. Electrically conductive nano-particles are durably anchored in the fibrils creating an electrically conductive network that prevents the formation of isolated chargeable areas and voltage peaks commonly found in conventional anti-static materials. This method can overcome the limitation of conventional methods, which is that the anti-static agent is easily washed off after a few laundry cycles.
Wrinkle resistance finish:
Wrinkling occurs when the fibre is severally creased. In case of when fibre or fabric is bent, hydrogen bonds between the molecular chains in the amorphous regions break and allow the chains to slip past one another. The bonds, reform in new places and fibre or fabric is held in the creased configurations. To impart wrinkle resistance to fabric, resin was used previously in conventional methods. The disadvantages of conventional resin applications include in the decrease of the strength of fibre and in abrasion resistance, water absorbency and dye-ability, as well as breathability. To overcome the boundaries of using resin, some researchers have employed TiO2 nanoparticles and nano-Silica to improve the wrinkle resistance of cotton and silk, respectively. TiO2 nanoparticle was employed with Carboxylic acid as a catalyst under UV irradiation to catalyze the cross linking reaction between the cellulose molecule and the acid. On other hand, nano-Silica was applied with Maleic anhydride as a catalyst; the results showed that the application of nano-Silica with Maleic anhydride could successfully improve the wrinkle resistance of silk.
A few marketing companies around the world have introduced anti-pollen fabrics and garments. It is claimed that particles of 30 nm sizes are attached to the surface of yarns thus the smoothness of the finish on the surface and the anti-static effect does not let pollen or dust come close. This is achieved by using the polymer which has antistatic or electro conductive composition e.g. Fluoro alkyl – methacrylate polymers). It is used in coats, blouses, hats, gloves, arm covers, bedding covers, etc.
Flame Retardant Finish:
Nyacol nanotechnologies TM has been developed colloidal antimony pentoxide which has been applied for flame retardant finish in textile. Colloidal antimony pentoxide has been offered as fine particle dispersion, for use as a flame retardant synergist with halogenated flame-retardants (the ratio of halogen to antimony is 5:1 to 2:1). Nano antimony pentoxide is used with halogenated flame-retardants for a flame retardant finish to the garments.
Table: Commercially available nano-particles for textile applications
|1||Silver nanoparticles||Anti-bacterial finishing|
|2||Fe nanoparticles||Conductive magnetic properties, remote heating.|
|3||ZnO and TiO2||UV-protection, fiber protection, oxidative catalysis|
|4||TiO2 and MgO||Chemical and biological protective performance, provide self-sterilizing function.|
|5||SiO2 or Al2O3 Nano-particles with PP or PE coating||Super water repellent finishing.|
|6||Indium-tin oxide nanoparticles||EM / IR protective clothing.|
|7||Ceramic nanoparticles||Increasing resistance to abrasion.|
|8||Carbon black nanoparticles||Increasing resistance to abrasion, chemical resistance and impart electrical conductivity, coloration of some textiles.|
|9||Clay nanoparticles||High electrical, heat and chemical resistance.|
In our concern nanotechnology is opening up a demand for higher precision, greater density and lightning speed combined with the intellectualization and miniaturization to progress into the next generation of apparels. The commercial application of nanotechnology has already been introduced in many prospect of textile arena. To create, alter and improve textiles at the molecular level and increase durability and performance beyond that of normal textiles are possible now. To continue this favorable trend, the textile industry should contribute more to research in nanotechnology and intensify its collaboration with other disciplines. With the changing trends and demands of the customer, it is the need of the age to make use of the technology available today. These applications and developments show that nanotechnology will emerge to dominate the textile field in future.
- “Functional finishing in cotton fabrics using zinc oxide nanoparticles”, A. Yadhav, V. Prasad, Bulletin of Materials Science, 29, 641, (2006); “Nanotechnology in Apparel Manufacturing: The New Horizon”, P. Jana, Bi-weekly Technology Communicator free newsletter, (July, 2006); “Nanofinishing in textiles”, N. Vigneshwaran, Nanowerk LLC, (Oct 13th, 2006).
- “Small steps now, big promises ahead”, P. Dhanapal and R. Anitha, The Indian Textile Journal, (May 2006);
- “A new approach to UV-blocking treatment for cotton fabrics”, Xin, J.H., Daoud, W.A., and Kong, Y.Y., Textile research journal, 97-100, (2004).
- “Keeping textiles fresh for longer”, S. Gupta, Journal for Asia on Textile & Apparel, (Feb 2008).
- “A big future for small science: Nanotechnology in textiles”, A Aravindan & D. Gopalakrishan, MMTI, 128-130, (Apr 2006), ATJ team Nanotechnology creating innovations Oct 2005, ATJ p- 95 K.
- “Nanotechnology Applications in Healthcare Textiles”, Marty G.