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Nanotechnology: A New Route to High Performance Textiles

Dr. MANGALA JOSHI

Professor, Department of Textile Technology, Indian Institute of Technology, Hauz Khas, New Delhi 110016, India E-mail: mangala@textile.iitd.ac.in

Abstract

A review and overview of the impact of nanotechnology on textiles is presented. It indicates a clear shift to nanomaterials as a new tool to improve properties and gain multi functionalities. Organized nano structures as those exhibited by fibres, nanocoatings, nanofinishing, nanofibers and nanocomposites have immense potential to revolutionize the textile industry with new functionality such as self cleaning surfaces, conducting textiles, antimicrobial properties, controlled hydrophilicity or hydrophobicity, protection against fire, UV radiation etc. without affecting the bulk properties of fibers and fabrics. Thus, we show that nanotechnology has the potential to being revolution in the field of technical textiles for the benefit of humanity. Keywords : nanocoatings, multifunctional, hydrophobic, layer-by-layer.

1. Introduction

Nano-science and nanotechnology combined, have revitalized material science and led to the development and evolution of a new range of improved materials including polymers and textiles through nanostructuring and nanoengineering. Nanotechnology is an emerging interdisciplinary area that is expected to have wide ranging implications in all fields of science and technology such as material science, mechanics, electronics, optics, medicine, energy and aerospace, plastics and textiles. Although Nanotechnology is still in its infancy, it is already proving to be a useful tool in improving the performance of textiles and generating worldwide

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interest. An overview on impact of nanotechnology on textiles indicates a clear shift to nanomaterials as a new tool to improve properties and gain multi functionalities. Organized nano structures as exhibited by either fibers, nanocoatings, nanofinishing, nanofibers and nanocomposites seem to have immense potential to revolutionize the textile industry with new functionality such as self cleaning surfaces, conducting textiles, antimicrobial properties, controlled hydrophilicity or hydrophobicity, protection against fire, UV radiation etc. without affecting the bulk properties of fibers and fabrics.

2. Nanotechnology in Textiles

The use of nanomaterials and nanotechnology based processes is growing at a tremendous rate in all fields of science and technology. Textile industry is also experiencing the benefits of nanotechnology in its diverse field of applications. Textile based nanoproducts starting from nanocomposite fibers, nanofibers to intelligent high performance polymeric nanocoatings are getting their way not only in high performance advanced applications, but nanoparticles are also successfully being used in conventional textiles to impart new functionality and improved performance. Greater repeatability, reliability and robustness are the main advantages of nanotechnological advancements in textiles. Nanoparticle application during conventional textile processing techniques like finishing, coating and dyeing enhances the product performance manifold and imparts hitherto unachieved functionality. New coating techniques like sol-gel, layer-by-layer, plasma polymerization, etc. can develop multi-functionality, intelligence, excellent durability and weather resistance to fabrics. The present article focuses on the development and potential applications of nanotechnology in developing multifunctional and smart nanocomposite fibers, nanofibers and other new nanofinished and nanocoated textiles. The influence of nanomaterials in textile finishing and processing to enhance

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product performance is discussed. Nanocoating is relatively a new technique in the textile field and currently under research and development. Polymeric nanocomposite coatings where nanoparticles are dispersed in polymeric media and used for coating applications is a promising route to develop multifunctional and intelligent high performance textiles. The most researched area to produce multifunctional, smart fibers is the preparation of nanocomposite fibers where the exceptional properties of nanoparticles have been utilized to enhance and to impart several functionality on conventional textile grade fibers. Nanofibers which are sub-micron size in diameter are gaining popularity in some specialized technical applications such as filter fabric, antibacterial patches, tissue engineering and chemical protective suits.

3. Nanotechnology Based Finishes and Coatings for Advanced Technical Textiles1-3

Nanotechnology has opened immense possibilities in textile finishing area resulting into innovative new finishes as well as new application techniques. Particular emphasis is on making chemical finishing more controllable, durable and significantly enhance the functionality by incorporating various nanoparticles or creating nanostructured surfaces. The unprecedented level of textile performances claimed for these nanofinishes such as stain resistance, antimicrobial, controlled hydrophilicity / hydrophobicity, antistatic, UV protective , wrinkle resistant and shrink proof abilities can be exploited for a range of technical textile applications such protective clothing, medical textiles, sportswear, automotive textiles etc.

Nanofinishes are generally applied in nanoemulsion form, which enables a more thorough, even and precise application on textile surfaces. They are generally emulsified into either nanomicelles, made into nanosols or wrapped in nanocapsules that can adhere to textile substrates easily and more uniformly. Since

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nanoparticles have a large surface area to volume ratio and high surface energy, they have better affinity for fabrics. Therefore these finishes are more durable, effective and do not adversely affect the original handle and breathability of the fabric. A range of different textile products and finishes based on nanotechnology has already been launched in the market. The recent developments in nanofinishing on textiles have been briefly described below:

4. Water and Oil Repellent (Hydrophobic) Nanofinishes

The premier range of Nano Care® and NanoPel® nanofinishes marketed by NanoTex Inc. USA are the next generation easy care finishes based on nanotechnology. These finishes which come under Resist spills TM Category protect the fabric against both water and oil based liquid stains / soils. Tiny whiskers aligned by proprietary “spines” are designed to repel liquids and are attached to the fibers utilizing molecular "hooks”. These whiskers and hooks are very-very small in fact no more than 1/1000th the size of cotton fiber. These whiskers cause the liquids or semisolids to roll off the fabric thus cause minimal staining, which can be removed with simple washing. Since the attached whiskers are of nanoscale size, they do not affect the hand, breathability of fabric and can withstand 50 home launderings.

5. Super Hydrophobic: Self Cleaning Nano Finishes

Many plants in nature including the Lotus leaf exhibit unusual wetting characteristic of super hydrophobicity (Fig. 2). A super hydrophobic surface is the one that can bead off water droplets completely; such surfaces exhibit water droplet advancing angles of 150o degree or higher. A self-cleaning surface thus results since the rolling water droplets across the surface can easily pick up the dirt particles to leave behind a clean surface. Taking the inspiration from the nature there have been several approaches researched to create super hydrophobic surfaces on textiles, which mimic the nanostructured Lotus leaf and therefore exhibit self-cleaning

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properties. Nano Sphere ®, a Lotus effect based textile finish has been developed, patented and commercialized by Schoeller Texil AG of Switzerland. Super hydrophobic silica coating film on cotton substrates, which are transparent and durable have been reported by W.A.Daud and coworkers of the Hong Kong Polytechnique University using low temperature sol-gel coating based on a low temperature process . This nanocomposite coating has new applications in daily use material and such as plastics or textiles and is an eco-friendly substitute for fluorocarbon based water repellant finish. There is less than 5% decrease in textile strength and tearing strength. The air permeability of the fabric remains unchanged. The washing durability of the coatings is also good.

Fig. 1. Lotus leaf effect and a SEM image of its surface [1,2]

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6. Photocatalytic Self Cleaning Finishes

Dr. John Xin and Dr. Walid Daoud of the Hong Kong Polytechnic University’s Nanotechnology Centre for Functional and Intelligent Textiles and Apparel developed a process for the sol gel coating on textile substrates at low temperature. They also claimed that photocatalytic self-cleaning properties could be imparted to the coated fabric on coating cotton with TiO2 nanoparticles that are about 20 nm in size (Fig. 3). The nanotitania coated fabrics maintain their antibacterial property up to 55 washes / home launderings and UV protection characteristics up to 22 washes.

Fig. 2. SEM images of (a) uncoated cotton fiber, (b) titania coated cotton fiber showing the morphological change in the surface structure, (c) higher magnification image of titania coated cotton fiber showing the shape and size of the titania particles, and (d) higher magnification image of a titania film coated on glass [1,2]

7. Hydrophilic Nano Finishes

The poor moisture absorption property of synthetic fabrics such as polyester and polyamides limits its applications in the

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apparel sector. The new range of hydrophilic nanofinishes 'Cotton Touch’ TM and ‘Coolest Comfort’ TM commercialized by NanoTex, USA makes the synthetic fabric look and feel like cotton. “Nanotouch ® gives durable cellulose wrapping over synthetic fibers such as polyester and polyamides. Cellulosic sheath and synthetic core together form a concentric structure to bring overall solutions to the drawbacks of synthetics such as static discharge, harsh handle and glaring luster. It can also last 50 launderings and expected to eliminate the decline in demand of synthetic microfiber and broaden the use of synthetics to new applications. ‘Nano Dry ®. Finish provides break through moisture wicking to draw moisture away from body while drying quickly. It improves the moisture absorption of polyamides and polyesters making them hydrophilic and comfortable. The main applications are in sportswear and close to body garments that require perspiration absorbency. The finish lasts 50 launderings.

8. Antibacterial Nanofinishes based on Nanosilver

A range of antimicrobial textile finishes and products have been reported and quite a few have been commercialized, which are based on much superior antimicrobial properties of silver in nanoform. Nano silver particles containing antimicrobial dressings have been incorporated in wound care and have gained wide acceptance in medical industry, as a safe and effective means of controlling microbial growth in the wound, often resulting in improved healing. A range of nano silver based medical textiles for health and hygiene has been developed and commercialized.

9. UV Protective Nanofinishes

Semiconductor oxides such as TiO2, ZnO, SiO2 and Al2O3 are known to have UV blocking property29-30. It is also known that nanosized TiO2 and ZnO particles are more efficient at absorbing and scattering UV radiation than the conventional size particles and thus were better able to block UV radiation as have much

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larger surface area to volume ratio. A lot of efforts have been made on the application UV bulking treatment to fabrics using nanotechnology. UV blocking treatments for cotton fabric has been developed using sol-gel method by Xin and coworkers. A thin layer of TiO2 nanoparticle is formed, on the surface of treated cotton fabric, which provides excellent UV protection, the finish is durable up to 50 home launderings. Apart from TiO2, ZnO nanorods of 10 to 50 nm in length were also applied to cotton fabric to provide UV protection. The rods exhibited excellent UV protection.

10. Antistatic Nanofinishes

Synthetic fibers such as Nylon and polyester are prone to static charge accumulation as they absorb less water. It has been reported that nanosized TiO2, ZnO whiskers, nanoantimony-doped tin oxide (ATO) and silane nanosol could impart antistatic properties to synthetic fibers. TiO2, ZnO and TiO2 nanoparticles are electrically conductive materials and help dissipate the static charge in these fibers.

11. Nanocoatings

Nanostructured surfaces are of great interest, due to their large surface area, which might yield high functionality. Nanocoating refers to the covering of materials with a layer on the nanometer scale (10 - 100 nm in thickness) or covering of a nanoscale entity to form nanocomposite and structured materials. Nanocoatings on Textiles have recently been explored using mainly processes such as plasma-assisted polymerization, self-assembly, sol-gel nanocoating and electrochemical deposition.

12. Nano Matrix: Self Assembly based nanocoatings

Toray Industries, Inc. have succeeded in developing a “nano-scale processing technology” that allows the formation of molecular arrangement and molecular assembly necessary to bring

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out further advanced functionalities in textile processing. This “nano-scale processing technology” named “NanoMATRIX” forms the functional material coating (10-30 nm) consisting of nano-scale molecular assembly on each of the monofilament that forms the fabric (woven / knitted fabric) (Fig. 4). “Nano-matrix” is based on the concept of “self-organization” by controlling the conditions like temperature, pressure, magnetic field, electrical field, humidity, additives etc. The application of this technology is expected to lead to development of new functionalities as well as remarkable improvements in the existing functions (quality, durability, feel etc) without losing the fabric’s texture.

Fig. 3. Nanomatrix Technology from Toray for nanocoatings on textiles through self -Assembly [1,2]

13. Plasma assisted nanocoatings

Plasma polymerization enables deposition of very thin nanostructured coatings (< 100nm) via gas phase activation and plasma substrate interactions. This dry and ecofriendly technology offers an attractive alternative to replace wet chemical process

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steps for surface modification (finishing) of textiles. Plasma polymerization can impart a wide range of functionalities such as water repellency, hydrophilicity, dyeability, conductivity and biocompatibility due to the nanoscaled modification of textiles and fibers. The advantages over conventional wet chemical processing is that it needs a very low material and low energy input, hence is environmental friendly, it does not affect the bulk properties of textiles and fibers such as feel (touch), handle, optical properties and mechanical strength. Moreover, these plasma-assisted coatings are more durable as compared to other surface modification techniques such as wet processes, radiation or simple plasma activation because nanoscaled plasma polymer coatings get covalently attached or bonded to textile surfaces.

Low-pressure plasma polymerization of unsaturated fluorohydrocarbons i.e. C3F6, C4F8 on selected textiles has been industrially performed using a semi continuous process to impart stain repellant properties on fabrics. Oil repellency grades of 4-5 were achievable in short treatment times (30-60 sec), which are superior to Scotch–Guard finished samples. The softness, feel, color, permeability, abrasion resistance, water performance and friction coefficient properties of original fabric were unaltered by these nanoscaled ultrathin (<100 nm) plasma coatings. The up scaling of plasma technology to industrial scale for textile applications is the major challenge faced by the researchers and technologists. Low-pressure plasma processes are still the state of the art technology, as effects produced by atmospheric plasma are comparatively weak and non-uniform. The other issues of concern are the efficiency of plasma polymerization process in terms of deposition rates and the right process speeds, so that they can be integrated with the current textile production lines. High investment cost and requirement of vacuum technology further limits the present application of this technology at industrial scale to only niche textile products. M/s EMPA, a Swiss based company, specializing in this area have mainly developed low-pressure plasma reactor for plasma-polymerized coatings.

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14. Polymer Nanocomposites

Polymer nanocomposites are the advanced new class of materials with an ultrafine dispersion of nanofillers or nanoparticles in a polymeric matrix, where at least one dimension of nanofillers is smaller than about 10nm. The volume and influence of the interfacial interactions increases exponentially with decreasing filler /reinforcement size and thus forms an additional separate phase known as interphase, which is distinct from the dispersed and continuous phases and hence influences the composite properties to a much greater extent even at low nanofiller loading (< 5%). Therefore, their properties are much superior to conventional composites. The interest in polymer nanocomposites further arises from the fact that, they are light weight as compared to conventional composites because of the low filler loadings, are usually transparent as scattering is minimized because of the nanoscale dimension involved and are still processable in many different ways including production of fibers with nanoscale fillers embedded in the polymer matrix. With these improved set of properties, they show promising applications in developing advanced textile materials such as- Nanocomposite fibers, nanofibers and other nanomaterial incorporated fibers and coated textiles for applications in medical, defense, aerospace and other technical textile applications such as filtration, protective clothing besides a range of smart and intelligent textiles.

Polymers nanocomposites thus offer tremendous potential when produced in fiber form and offer properties that leapfrog those of currently known commodity synthetic fibres. Nanocomposite fibres that contain nanoscale embedded rigid particles as reinforcements show improved high temperature mechanical property, thermal stability, useful optical, electrical, barrier or other functionality such as improved dyeability, flame retardance, antimicrobial property etc. These novel biphasic nanocomposites fibres in which dispersed phase is of nanoscale dimension, will make a major impact in tire reinforcement, electro-

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optical devices and other applications such as medical textiles, protective clothing etc. The work on spinning of nanocomposites started about seven years ago and several research groups across the world are exploring the synthesis, fiber processing, structure- property characterization and correlation and molecular modeling of these unique new composites fibers. Polymeric nanocomposite fibres have been mostly spun through three basic methods of fiber spinning -Melt spinning, Solution spinning and Electrospinning. Although, most of the research reports on polymeric nanocomposites is where it has been studied in form of films or moulded specimens and very few reports on their spinning into Nanocomposite fiber form. However, there are some reports on composite fibers based on all the three major types of nanofillers viz layered silicate nanoclays (MMT), carbon nanotubes (CNT) and nanofibers, metal oxide nanoparticles (TiO2, ZnO, SiO2 etc.) and hybrid nanostructured materials such as POSS have been reported in literature.

15. Polymeric Nanofibers

Recently, there has been an increased interest in producing nanofibers that are sub micron size in diameter. Typically conventional melt blown ultrafine fiber diameter ranges from 2000 to 5000 nm, whereas polymeric nanofibres ranges from 50 to 500 nm. Nanofibers are characterized by extra ordinary high surface area per unit mass (for instance nanofibres with 100nm in diameter have a specific surface of 1000 m2/g) high porosity and light-weight. These unique properties of nanofibres make them potential candidates for a wide range of application such as filtration, barrier fabrics, protective clothing, wipes and biomedical applications such as scaffolds for tissue engineering. Electrospinning is a process that produces continuous polymeric nanofibres (diameter in submicron range) through an action of an external electric field imposed on a polymer solution or melt. Recently, electrospinning has also been extended to making nanofibres from polymer

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nanocomposites, incorporating nanoclays, CNTs and other nanoparticles and adding a new dimension to nanofibres. These nanocomposite fibers when deposited over textile substrates can be further used to manufacturer fabrics, antistatic materials, electromagnetic shielding materials, high performance separation medium, reinforcing materials, electrical and thermal conductivity materials, wave absorbing materials etc.

Fig. 4. Electrospun nanofibrous web under SEM [1,2]

Fig. 5. Schematic diagram of electrospinning set up [1,2]

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16. Nanocomposite Fibers

At Textile Deptt. IIT Delhi, we have investigated nanocomposite fibers based on all the three major types of nanofillers viz layered silicate nanoclays (MMT), carbon nanotubes (CNT) and nanofibers, and hybrid nanostructured materials such as POSS.

Compatibilized polypropylene/nanoclay composite filaments were produced by melt intercalation route using twin screw compunder coupled to a fiber take up device and drawing machine and characterized to study the effect of the compatibilizer and the role of nanoclay in improving the properties. The compatibilizer used was Maleic anhydride grafted Polypropylene (PP-g-MA). Clay loadings of up to 1 wt % with up to 3-wt % of the compatibilizer were studied. The dyeability properties of these filaments showed that nanocomposite filaments took up disperse dyes unlike the neat PP filaments which have to be dope dyed. There was a significant improvement in tensile, thermal, dynamic mechanical and creep resistance properties of PP/nanoclay composite filaments over neat PP filaments4.

Another development was making high performance fibers based on polymeric nanocomposites based on a novel class of hybrid nanostructured filler, Polyhedral Oligomeric Silsesquioxane (POSS). The system chosen for the study is the simple ‘octamethyl POSS’, a molecular silica as the nanofiller and HDPE as the polymeric matrix. At comparatively very low loadings (0.25-0.5 wt %), POSS actually gives a lubricating effect and facilitates the drawing of filaments, which results in higher tensile strength and modulus. With increase in POSS concentration beyond 1 wt %, POSS existing as nanocrystals/aggregates starts hindering the orientation of HDPE chains leading to a gradual fall in tensile strength and modulus. Incorporation of POSS also modifies the thermal degradation behaviour of HDPE and broadens the temperature range of thermal degradation. The HDPE-POSS

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nanocomposite filaments also exhibit better UV resistance than neat HDPE filaments, which may be attributed to the scattering/reflective action of POSS5-8.

An attempt to explore the feasibility of producing filaments from polyurethane (PU) /clay nanocomposites and compare their structure and properties vis-a-vis neat PU filaments has been carried out as a part of doctoral thesis by our research group. This work reports the production of filaments from neat polyurethane and polyurethane/clay nanocomposite by dry-jet-wet spinning; a technique being used for the first time for this system. An organomodified nanoclay was used as a filler and thermoplastic polyurethane as the matrix. Dispersed nanoclay in PU matrix has induced both external morphological changes as well as internal micromorphology. Nanoclay dispersion reduces the stretchability by enhancing the void content of the nanocomposite filaments. Modulus and tenacity are enhanced significantly in the presence of nanoclay at low concentrations; nevertheless elongation and elastic recovery are marginally affected. Thermal studies suggest that a significant improvement in thermal stability of PU/clay nanocomposites filaments is due to hybridization with inorganic nanoclay. High thermal shrinkage at low clay concentration indicated high orientation due to good dispersion and exfoliation of clay in filaments. Boiling water shrinkage and water swelling also indicated high orientation and reduced swelling due to incorporation of clay. Fire retardant properties studied by cone calorimetry shows excellent fire retardant properties at low clay content (0.25 wt %). Dyeability properties of nanocomposite fibres also get significantly enhanced in the presence of nanoclay. Weatherability resistance of PU/clay filaments are significant only at higher clay concentration (~ 1 wt %).

Polyamide or nylon 6/clay nanocomposites have been widely investigated due to their much superior tensile strength and modulus, improved heat resistance (heat distortion temperature increases from 65°C to 120°C) as well as excellent gas and water

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barrier propertie over their neat nylon 6 counterparts. In a study by our research group nylon/clay nanocomposite fibers were prepared by melt intercalation route and spun into filaments which were converted into cords and tested for tire cord related properties such as tensile strength, rubber to cord adhesion and fatigue resistance. The nylon/clay nanocomposite cords exhibited improved tensile strength (21%) as well as improved reubber to cord adhesion (35%) but slightly reduced fatigue resistance as compared to neat nylon filaments9.

17. Nanocomposite Coatings

A glance at the literature available shows interesting applications of polymer nanocomposites as coatings with attractive combinations of properties not achievable by neat polymeric conventional coatings. Novel Polyurethane/ MMT (clay) based nanocomposites as coatings for inflatables has been explored in an ongoing research project at Department of Textile Technology, Indian Institute of Technology, Delhi by M Joshi et.al. The coated fabrics showed improved gas barrier property without affecting the transparency and tear strength. Clays are believed to increase the barrier properties by creating a tortuous path that retards the progress of gas molecules i.e. gas diffusion through the matrix resin10.

A significant achievement of our group has been the work where novel hybrid nanographite particles have been synthesized via co-deposition of iron and nickel on nanographite particles using fluidized bed electrolysis, a simple and eco-friendly technique11. These metal coated nanographite particles were dispersed in polyurethane matrix and showed a significant enhancement in microwave absorption as a thin coating and at relatively low loadings (<10 wt %). The microwave absorption frequency range further widened to X (8 – 12 GHz) and Ku (12 – 18 GHz) bands. These nanocomposite coatings were truly multifunctional as they also enhanced the gas barrier, UV

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resistance and conducting property of the coatings. The flexibility of such nanocomposite coatings is almost retained at 10 wt% loading and the durability is found to be excellent under accelerated weathering conditions. These excellent results have been reported for the first time using novel hybrid nanographite particles in polyurethane matrix and there are no similar literature reports for other RAM coatings12-13. This work has got us the “National Award (2011-2012)” from Ministry of Chemicals and fertilizers”, Govt. of India for Innovation in Downstream Petrochemical Industry in the Category of Academic Research and Development.

Fig. 6 : FeNiNG dispersed polyurethane film under tapping mode of AFM: at low magnification (a) Height image and (b) Phase Image; at high magnification (c) Height image and (d) Phase Image [12, 13]

The developed Polyurethane/hybrid nanographite based nanocomposite in coating or film form have the potential defence applications as camouflage coatings, covering or envelop on army vehicles, naval ships, military establishments, etc. for an effective microwave shielding effect. These flexible polymer nano-

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composites also offer the possibility of many other industrial applications in microsystem technologies, as microwave or radar absorbent material; in astronautics and for anticorrosive coatings.

18. Nanocoatings

Layer-by-layer assembly (L-b-L) is a unique technique for the fabrication of composite films and deposition of coatings with nanometer precision. Since the introduction of polyelectrolyte multilayer architectures formed by the alternate deposition (layer-by-layer self assembly) of polycations and polyanions from solution to a solid support by Decher et al. in 1991, numerous papers have been published using this very simple yet versatile technique to modify organic or inorganic solid surfaces. Application of L-b-L process to modify the surfaces of textile substrates i.e fiber or fabrics has not been either extensively studied or understood. Recently there have been only few reports on depositing nanolayers of polyelectrolytes on cotton, silk and nylon fibres which seem to be a promising technique for future applications.

In our work on nanocoatings on textiles using L-b-L technique we report nanocoating of cotton substrate using L-b-L process, to impart various functional properties on cotton textiles such as antimicrobial , self cleaning, hydrophilicity / hydrophobicity etc.14. Cotton fibers offer unique challenges to the deposition of nanolayers because of a unique cross-section as well as chemical and physical heterogeneity of its surfaces. Cationic cotton surface has been successfully coated with alternate layers of anionic and cationic polyelectrolytes, i.e. poly (sodium 4-styrene sulphonate) and poly (allylamine hydrochloride) using L-B-L technique. A study by M. Joshi, Wazed Ali, S. Rajendran reports that the multilayer formation of polyelectrolytes on cotton surface is sensitive to different process parameters such as pH, temperature, concentration of polyelectrolyte solution, dipping time and addition of salt15. Layer by layer technique can also be utilized to

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create multifunctional textile surface as antifouling, self cleaning and water resistant coatings for micro-fluids channels and bio sensors. A stable lotus leaf structure has been mimicked to create super hydrophobic surfaces using silica nanoparticles and a low surface energy finish on cotton substrate14.

Antimicrobial silver nanoparticles can be immobilized on nylon and silk fibers by this method. The sequential dipping of nylon or silk fibers in dilute solutions of poly(diallyldimethylammonium chloride) and silver nanoparticles capped with poly(methacrylic acid) lead to the formation of a colored thin film possessing antimicrobial properties. The amount of deposition on both silk and nylon fibers increases as a function of the number of deposited layers though the L-B-L coating on the nylon fibers is not as uniform as on the silk fibers. The deposition of bilayers onto the fibers results in significant bacteria reduction for the silk and the nylon fiber. New antimicrobial synthetic or natural fibers can be designed through this technique.

In a study by M. Joshi et al, L-B-L nanocoating has been carried out on cotton fabric using chitosan as the cationic polyelectrolyte and poly sodium-4-styrene sulfonate as the anionic polyelectrolyte. The process is assisted with ultrasonic treatment for uniform very thin (few nm) deposition of the bi-layers. Thus produced fabric has good antimicrobial property; however, the feel, flexibility and breathability of the fabric are not affected16. Further chitosan nanoparticles and silver modified chitosan nanparticles have been synthesized and the effect of surface charge, size and shape has been studied to optimize the antibacterial property17,18 and then these have been applied on cotton as well as polyester surface using L-b-L self assembly approach19,20.

19. Future Trends

Nanotechnology has thus emerged as the ‘key’ technology, which has revitalized the material science and has the potential for

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development and evolution of a new range of improved materials including polymers and textiles. However there are many challenges in the development of these products, which need to be intensively researched so that the wide range of application envisaged can become a commercial reality. An excellent dispersion and stabilization of the nanoparticles in the polymer matrix is crucial to achieving the desired nano effects. The tendency to agglomerate due to extremely high surface area is the major problem facing the effective incorporation of nanoadditives in coatings/finishing as well as in nanocomposite preparation. Surface engineering of nanoparticles and combining them with functional surface-active polymers can bring the nanoparticles onto fibers/textiles without losing their superb, nanoscopic properties.

To conclude nano-technology, definitely has the potential to being revolution in the field of technical textiles. There is however a word of caution because industrial commercialization of the nano technology products can become a commercial reality.

The issues are- (i) Large scale production of nano particles and their cost (ii) Impact of uncontrolled release of nanoparticles in the

environments and their effect on human health and ecology widely covered under the domain ‘nano-toxicology’

(iii) Practical philosophy and ethics on the wide spread use of nanotechnology based products.

References

1. M. Joshi and A. Bhattacharyya (2011) Nanotechnology : A New Route to High Performance and Functional Textiles. Textile Progress 43 (3), 155-233.

2. M Joshi (2008) ‘The Impact of Nanotechnology on Polyesters, Polyamides and other Textiles”, ‘Advances in Polyesters and Polyamides”. Woodhead Publishing, Ltd. Cambridge, UK.

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3. M. Joshi, (2005) Nanotechnology: Opportunities in Textiles, Indian Journal of Fiber and Textile Research, 30. 477-479.

4. M. Joshi and V. Viswanathan (2006) High Performance Filaments from compatibilised PP/clay nanocomposites, Journal of Applied Polymer Science. 102(3) 2164-2174.

5. M. Joshi and B. S. Butola (2007) Isothermal crystallisation of HDPE/POSS Nanocomposite: Effect of POSS as Nanofiller, Journal of Applied Polymer Science. 105(2), 978-985.

6. M. Joshi, B. S. Butola, G. Simon and N. Kukalevab (2006) Rheological and viscoelastic behaviour of HDPE/ Octa methyl POSS nanocomposites, Macromolecules. 39, 1839-1849.

7. Sachin Kumar, B S Butola and M Joshi (2010) Preparation of hybrid Polypropylene/POSS nanocomposite monofilaments by radiation induced grafting. Fibers and Polymers, 11(8), 1137-1145,

8. B. S. Butola, M.Joshi, and S. Kumar (2010) Hybrid Organic-Inorganic POSS (Polyhedral Oligomeric silsesquioxane)/Polypropylene Nanocomposite Filaments, Fibers and Polymers. 11(3) 1137-1145.

9. M Joshi, D Biswas, A Sarvanan and R Mukhopadhyay (2012) Nylon 6/ Nanoclay filaments and their cords, Journal of Applied Polymer Science. 125,E224-E234.

10. M. Joshi, K. Banerjee, Prasanth R and V Thakare (2006) Polymer-Clay Nanocomposite based Coatings For Enhanced Gas Barrier Property. Indian Journal of Fiber and Textile Research, 202-213.

11. A Bhattacharyya and M.Joshi (2011) Co-deposition of Iron and Nickel on Nanographite for Microwave Absorption through Fluidized Bed Electrolysis. International Journal of Nanoscience, 10 (4-5), 1125 – 1130.

12. Bhattacharyya & M. Joshi (2010) Microwave Absorbent Nanocomposite Films of Iron-Nickel Nanographite in Thermoplastic Polyurethane Matrix. Journal of Nanostructured Polymers and Nanocomposites, 6 (3) 73-78.

13. Bhattacharyya & M. Joshi (2012) Functional Properties of Microwave Absorbent Nanocomposite Coatings based on Thermoplastic Polyurethane-based and Hybrid Carbon-based Nanofillers. Polymers for Advanced Technologies, 23(6), 975-983.

14. M Joshi, A Bhattacharya, N Agrawal and S Parmar (2012) Nanostructured Coatings for Superhydrophobic Textiles. Bulletin of Materials Science, 35(6) 933-938.

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15. S. Wazed Ali, S. Rajendran and M. Joshi (2010) Effect of Process Parameters on Layer-by-layer Self-assembly of Polyelectrolytes on Cotton Substrate. Polymers & Polymer Composites, 18, 175.

16. M. Joshi, R. Khanna, K. Jha, R. Shekar (2011) Nanocoating of chitosan using layer-by-layer self-assembly approach on cotton textile substrate. Journal of Applied Polymer Science, 119, 2793-2799

17. S. Wazed Ali, S. Rajendran and M. Joshi (2010) Modulation of size, shape and surface charge of chitosan nanoparticles with special reference to antimicrobial activity. Applied Science Letters, 3, 1-9.

18. S. Wazed Ali, M. Joshi and S. Rajendran (2011) Synthesis and Characterization of Chitosan Nanoparticles with Enhanced Antimicrobial Activity. International Journal of Nanoscience , 4&5, 979-984.

19. S. Wazed Ali, S. Rajendran and M.Joshi (2011) A Novel Self-Assembled Antimicrobial Coating on Textiles using Chitosan Nanoparticles. AATCC Review, 11(5), 49-55.

20. S. Wazed Ali, S. Rajendran and M. Joshi (2011) Synthesis and characterization of chitosan and silver loaded chitosan nanoparticles for bioactive polyester. Carbohydrate Polymers, 83, 438-446