35 Role of Nano technology is textile finishing

S. Karpagam Chinnammal

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1.  Introduction

 

Nanotechnology is an emerging technology. It is gradually gaining global attention as it has vast potential in a broad range of end uses. It is all about making products from very small components to achieve improved properties and functionality. It is a technology that makes existing application work more efficiently. Nanotechnology has profit-making potential for the textile industry and is an upcoming technology in the area of textiles. Fabric finishing has taken new routes and has shown a great potential for significant improvements by application of Nanotechnology.

 

2. Learning objectives

 

o  To understand about Nano technology

o To gain knowledge about the finishing agents used in Nano finishing and its application

o To gain insight into the various nano finishes in textiles o To learn about the characteristics of Nano finishing

 

3. Nanotechnology

 

Nanotechnology is defined as ‘The precise manipulation of individual atoms and molecules to create layer’. Nanotechnology according to the National Nanotechnology Initiative (NNI) is 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.

 

Nanotechnology is a field of applied science focused on the design, synthesis, characterisation and application of materials and devices on the nano scale. The term Nano is a Greek word meaning ‘dwarf’. Nanotechnology is concerned with materials that are very small i.e 1 to 100 nm in length. 1 nanometer (nm) is one billionth of meter or 10-9 m. One Nano meters is about 100000 times smaller than the diameter of the human hair.

 

The basics of Nanotechnology are that properties of substances significantly change when size is reduced to the nanometer range. When a large material is divided into small size particles in the nanometer range, the individual particles show astonishing properties, different from those of the large material. For example: ceramics have a property of brittleness but if the grain size of the material is converted into nano-particles then the particles will be deformable.

 

The use of nanotechnology in the textile industry has increased rapidly due to its exceptional and valuable properties. The chief areas of application of nanotech in textiles are Nanofibres, nanotubes and nano finishing.

 

4.  Nano finishing

 

Nano finishing is the application or coating of the surface of textiles with Nano particle to create active surfaces with exceptional properties.

 

4.1.Importance of Nano finishing

 

Reducing the size of particles to nano scale primarily changes the properties of the material.

  • The size of the particle plays a major role in determining their adhesion to the fibres. Largest particles agglomerates and will be easily removed from the fiber surface, while the smaller particles penetrate deeper and stick strongly into the fabric .
  • The large surface area to volume ratio of nano particles makes it easy for them to attach to fibre or fabric.
  • They have higher efficiency and durability to the functions imparted by particles through the life of the fabric.
  • The nano technology based thin films and coatings are invisible and do not blur colour and brightness of the textile substrate.
  • The breathability and hand or feel of the textile is not affected by the coating of nanoparticles

4.2.Finishing agents

 

There are several Nano particles. Zinc oxide, Titanium Dioxide and Silver oxide are popularly used in the nano finishing of textiles. Metal oxide nano particles are more preferable than nano silver because of cost considerations. Zinc oxide and Titanium dioxide are non toxic and chemically stable under exposure to high temperature and are capable of photo catalytic oxidation. The application of nano particles to textile materials is aimed at producing finished fabrics with different functional performances.

 

4.3. Preparation and application of Nano materials

 

4.3.1. Preparation

  • Six methods commonly used to produce nano material are
  • Plasma arcing
  • Chemical vapour deposition Electro deposition
  • Sol gel synthesis Ball milling
  • Use of natural nano particles

4.3.2. Application

 

Nano particles are applied on textiles by a two stage process. Primarily it is the manufacture of new stable nano material, which must, be protected against properties defined by the size of the particles. The second step is the creation of the foils, emulsions and dispersions that can be applied to the textile product.

 

Nano particles are generally applied to textiles by coating using a composition of nanoparticles, a surfactant, ingredients and a carrier medium. Coating techniques include Spraying-the coating is sprayed onto textile on specific areas Dipping and soaking-in an immersion container and followed by drying Transfer printing such as rotary, flexography and inkjet Washing, accomplished by using a washing solution containing nano particles during wash or rinse cycles in a washing machine Padding, where nano particles are attached to the fabrics with the use of padder applied under pressure Sol-gel method could be an effective procedure to entrap organic and inorganic compounds with various functionalities on different surfaces

 

In conventional finishing techniques, pad –dry-cure, thermal radiation or chemical methods are generally employed to fix theses nano particles on textiles. The process in such cases either involves several steps or is chemical intensive. The coatings produced are thick, unstable and do not allow the fabric to breathe properly. Recent studies show that LbL ie Layer by layer assembly can produce ultra thin, tranmissive and stable coaings and is a chemically mild alternative to the conventional process.

 

Layer by layer assembly ( LbL) method is a unique technique developed for production of thin composite films on solid surfaces. The process begins by charging a substrate appropriately, followed by immersion in an oppositely charged polyelectrolyte solution and rinsing. The charged surface attracts the oppositely charged polyelectrolyte and binds it with the help of strong electrostatic bonds. After rinsing, the substarte coated with a mono layer is treated with a solution of oppositely charged electrolyte solution. Repetition of this cycle can be used to deposit up to 20 ultra thin layers.

 

 

5.  Application of nano technology in textile finishing

 

5.1.Anti-microbial Finish

 

Textile materials are good media for growth of microorganisms. Nano sized zinc oxide, titanium dioxide and silver have been used to impart antibacterial characteristics to the textile substrate. Metallic ions and metalic compounds exhibit specific level of sterilizing effect. The sterilizing effect is produced by the conversion of a part the oxygen present in air or water, into active oxygen through catalysis with metallic ion, and thus dissolves the organic substances. Also the number of particles in unit area is increased by using nano particles, there by maximizing the anti bacterial effect.

 

Silver ions have broad spectrum of anti microbial activities. The method of producing durable silver containing antimicrobial finish is to encapsulate a silver compound or nano particle with a fibre reactive polymer like poly (styrene co-maleic anhydride) .Nano-silver particles have a very large relative surface area, thereby increasing their contact area with bacteria or fungi, and greatly improving their bactericidal and fungicidal effectiveness. Nano-silver is highly reactive with proteins. The cellular metabolism and growth of the microbes will get harshly affected when the nano silver particles are in contact with them. It also suppresses respiration and transport of substance into the microbial cell membrane. The growth and development of the bacteria and fungi that cause infection, odor ithciness and sores are restricted. Silver is a safer anti-microbial agents in comparison with some organic anti-microbial agents because of the risk of their harmful effects on the human body. Nano silver particles have been applied on socks, health care products such as dressings for burns, skin donor and recipient sites to prevent the growth of bacteria.

 

Titanium dioxide and Zinc oxide are photo catalysts ; 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 photo catalyst. 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 photo catalyst it will combine with O2 – and OH- respectively and turn into carbon di oxide and water. This cascade reaction is called oxidation-reduction. Through the reaction, the photo catalyst is able to decompose common organic matters in the air such as odor molecules, bacteria and viruses. It has been found that the photo catalytic activity of nano TiO2 and ZnO could prove effective in protection against bacteria.

 

5.2.Antistatic effect

 

Synthetic fibres develop static charges since these fibres have very little capacity to absorb water. The anti static properties could be imparted to synthetic fibres by the application of nano sized Titanium Dioxide, Zinc oxide whiskers, nano antimony-doped tin oxide and silane nanosol. TiO2 and ZnO whiskers, nano antimony-doped tin oxide are electrically conductive in nature and are able to effectively eliminate the static charge that is accumulated on synthetic fabrics. 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 present in them.

 

5.3.UV protection

 

A UV-protective textile provides protection from UV light and in addition reduces the risk of skin injury related to exposure. UV blockers have been used in the UV protection and these are of organic and inorganic types. The inorganic types are non toxic and chemically stable under exposure to both high temperature and ultra violet light and are preferable to organic ones. They are generally semi conductor oxides which include titanium dioxide, zinc oxide, silicone dioxide and aluminium oxide. Of these, titanium dioxide, zinc oxide is commonly used. The nano sized titanium dioxide and zinc oxide have been found to be more effective in absorbing and scattering UV light as compared with their conventional counterparts, and are therefore able to block the UV light. This could be because of the the larger surface area per unit mass and volume of nano sized particles as compared with conventional ones.

 

A remarkable UV protection is achieved with the formation of a thin film of titanium dioxide on the surface .Besides the UV protection has also been attained through application of zinc oxide nano rods ranging in length between 10 to 50 nm .

 

Nano clay particles of montmoriblonite is one of most commonly used UV blocker. These types of substances contain hydrogen aluminosilicates, having difference in the chemical composition and crystal structures. The clay nano particles have a property of locking UV light. It also has electrical, chemical and heat resistance. Application -pad-dry-cure. Enduse-Shirtings, sportswear and beachwear

 

5.4.Wrinkle resistance

 

In conventional finishing, wrinkle resistance is imparted usually using resin. But the application of resin results in decrease of tensile strength of fibre, water absorbency, abrasion resistance, dyeability and breathability. In order to overcome the setbacks of the conventional resin, nano titanium dioxide and nano silica has been developed so as to improve the wrinkle resistance of cotton and silk respectively. Nano titanium dioxide has been used with carboxylic acid as a catalyst under UV radiation, which catalyze the cross linking reaction between the cellulose molecule and acid. When nano silica has been applied on silk using maleic anhydride as catalyst, the wrinkle resistance has been efficiently improved. The fabric is treated with small particles about 10nm in dimension. These tiny particles crosslink with cellulose to give desired amount of wrinkle resistance and they cover the fabric so densely that it does not allow liquids to pass through it. But breathability of the fabric is practically unaltered.

 

5.5. Water repellency

 

The water repellent property of fabric is improved through the creation of nano whiskers. These are hydrocarbons and are 1/ 1000th the size of a cotton fibre. They are added to the fabric to produce peach fuzz effect on the fabric without affecting its strength. The spaces between the whiskers in fabric are smaller than a drop of water, but it is larger than the water molecule. The water therefore remains above the whiskers and also above the fabric surface. However it can pass through the fabric with applied pressure. The performance is permanent while maintaining breathability.

 

Besides the nano tex discussed above, another interesting development, known as the ‘Nano sphere” has been evolved to make water repellent fabrics. The impregnation of nano sphere on the fabric is done using gel forming additives that repel water and avoid dirt particles getting attached on fabric surface. The mechanism is similar to that occurring in the lotus plant.

 

The surface of the lotus plant is highly hydrophobic and has rough texture. When the water drops fall on the lotus leaf, they tend to form beads and will roll off even if the surface is slightly sloped.thus lotus leaf remains dry even during heavy rain. Moreover the water drop gathers minute dirt particles as they roll, and hence the lotus plant leaves remains clean even during rainfall.

 

Hydrophobic property could be imparted to a cotton fabric by coating it with a thin nano paticlulate plasma film. Fluorocarbon chemical was applied to deposit a nano particulate hydrophobic film onto a cotton fabric surface to improve its water repellent property. As the cotton fabric surface was rough, a high degree of phobocity has been attained, while maintaining the softness and abrasion resistance.

  5.6.Self-Cleaning Fabric

 

There are basically two types of self-cleaning surfaces involving nanotechnology. In the first place extremely water repellent, microscopically rough surfaces are created: dirt particles can hardly get a hold on them and are, therefore, removed by rain or by a simple wash in water. By using nanotechniques, cloth is covered in a fuzz of tiny whiskers which creates a cushion of air around the fibre. When water hits the fabric, it beads on the points of the whiskers, the beads compress the air in the cavities between the whiskers creating extra buoyancy. In industrial terms, the material has been rendered super-non wettable or superhydrophobic. The whiskers also create lesser points of contact for dirt. When water is applied to dirty fabric, the dirt adheres to the water much more 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. Thus the concept of “Soil-cleaning” is based on the leaves of the lotus plant.

 

The second method is by photo-catalytic layers: The TiO₂ is a known catalytic compound. The fabric is treated with nano crystalline titanium oxide to impart photo catalytic self cleaning property. It shows it`s catalytic property by the absorption of a photon and jumped to the conduction band from the valance band. That is able to remove the organic pollutants and xenobiotics from the textile materials. Fouling organic material is destroyed by solar irradiation.

 

Super hydrophobic surfaces have water repellent properties. Surfaces with high contact angle also exhibit a self cleaning effect. Water repellent hydrophobic surfaces can be produced using roughness of nanoparticles combined with hydrophobicity of polymer matrix. Attempts are made to incorporate hydrophobic compositions such as organic silicon and organic fluorine into the synthesised materials.

 

5.7. Anti pollen finish

 

This finish is achieved using a polymer like Fluoroalkyl – acrylate polymers which have antistatic or electro conductive composition. Nano particles of 30nm sizes are applied on to the surface of yarns. The smoothness of the finish on the surface and the anti-static effect does not let pollen or dust come close. It is used in coats, blousons, hats, gloves, arm covers, bedding covers, etc.

 

5.8. Flame Retardant Finish

   Flame retardants are chemicals used in textiles that inhibit or resist the spread of fire. They make it more difficult for fabrics to ignite, and makes them burn slower and make fabrics self-extinguish when the flame is removed. Flame retardants allow time to remove the clothing or put out the flames.

 

Fire Retardant Coating is an advanced polymer-based nanotechnology that provides fire and flame protection to a broad range of materials without the risk of toxic by products during combustion. These protective coatings may be applied to metallic, ceramic, polymeric, and composite structures using simple and low-cost coating techniques.

 

Nano antimony pent oxide particles along with Halogenated flame-retardants(1:2-1:5) are used for the flame retardant finishing. Nano clay play an important role in flame retardant textile coating. While the polymer is burned and gasified during combustion nano clays accumulate at the surface and form a barrier to oxygen diffusion, thereby slowing down the burning process.

 

It can be applied by -pad/spray –dry-cure method. End use- bed sheets, curtains, fire suits

 

5.9. Odour fight Finish

 

Tourmaline is a natural mineral which in contact with oxygen, carbon di oxide and water molecules in the air promotes electrolytic dissociation and emits negative ions. These fibers release undetectable negative ions and infrared rays that destroy odour-causing bacteria. The negative ions create a magnetic field that inhibits the reproduction of bacteria, thus eliminating odour and lowering the risk of skin infection or irritation. Far infrared rays are absorbed by cells not just in the skin but throughout the body – causing all the individual atoms being vibrated at a higher frequency, which speeds up the metabolism and the elimination of wastes.

 

6. Characteristics of Nano finishing in textiles

  • Nano protective layer is difficult to detect with the naked eye.
  • Nano-materials allows good ventilation and reduces moisture absorption, resulting in enhanced breathability while maintaining the good hand feel of ordinary material.
  • Nano  processed  products are toxic  free
  • This technology embraces environmental friendly properties.
  • Fabrics stay bright, fresh looking and are more durable than ordinary materials.
  • Nano – processed Materials have protective coating, which is water and beverage repellent.
  • Manufacturing cost is low, adding value to the products.
  • When a substance is manipulated at sizes of approximately 100 nm, the structure of the processed clothing becoming more compressed. This makes clothing stain and dirt resistant.
  • The crease resistant feature keeps clothing neat
  • Saves time and laundering cost.

 

7.Summary

 

Nanotechnology is a growing interdisciplinary technology often seen as a new industrial revolution.The advent of Nanotechnology has spured significant developments and innovations in the field of textile technology. Nano finishes being developed for textile substrates are at their infantile stage but appear to hold many promises in the varied fields of multifunctional applications. Nano finishing can replace the traditional finishing technique of textile products with products of superior quality and lower production costs. In future, one can expect to see many more developments in textiles based on Nano Technology. Definitely these tiny particles are going to shape our future .

 

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REFERENCE

 

  1. Nano finishing of textiles , Dr.N.Gokarneshan, Abishek publications, Chandigarh and New delhi,2013
  2. A.P.S.Sawhney1 and B. Condo, K.V. Singh, S.S. Pang and G. Li and David Hui , (2008). Modern Applications of Nanotechnology in Textiles. Textile Research Journal: SAGE Publications Los Angeles, London, New Delhi and Singapor.
  3. http://www.slideshare.net/sandeepmittal62/nano-finishing-of-textiles
  4. http://www.scribd.com/doc/26045540/Nanotechnology-Applications-in-Textiles Henestrota_full_93_04
  5. www.Modern applications of nano technology in textile.
  6. http://xa.yimg.com/kq/groups/23138315/1120218164/name/BeringerNano_MFC07_En.p df
  7. http://site.icce-nano.org/Clients/iccenanoorg/hui pub/2008modern applications of nanotechnology in textiles.pdf

 

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