Functional Nano Finishes For Textiles

Mythili Sardar Vallabhbhai Patel Institute of Textile Management, 1483, Avinashi road, Peelamedu, Coimbatore – 641 004 Department of Textile technology, PSG College of Technology, Peel

Functional

Nano Finishes

For Textiles By: D Gopalakrishnan & K.G Mythili

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)

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

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

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 TiO2, ZnO, SiO2 and Al2O3 Among these

semiconductor oxides, titanium dioxide (TiO2) 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 Tio2

(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

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) Ti02 e- + p (Exiton)

H0+p H0

Ti4 Ti3

Ti3 [ Ti4 O2 abs]

[Ti4 O2 abs] + H20 Ti4 + H0 + H02

ii).Overall reaction

H20 + O2 hv HO + HOTiO

Titanium dioxide is a photo catalyst, 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)

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-TiO2 could provide effective protection against bacteria and the discoloration of stains, due to the photocatalytic activity of nano-TiO2 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)

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

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