Functional Nano Finishes For Textiles

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Functional

Nano
Finishes
For
Textiles






By: D. Gopalakrishnan & K.G. Mythili


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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)

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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

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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.







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Figure.5. Mechanism of Nano Sphere on textiles applied by NanoSphere technology

(a) Water droplet rolls down a plant, (b) Water droplet rolls down a lotus plant

3. UV-protection

Previously organic and in organic UV absorbers were coated on the textile material
they prevent UV radiation effectively but they are less durable. UV blockers are usually
certain semiconductor oxides such as TiO
2
, ZnO, SiO
2
and Al
2
O
3
. Among these
semiconductor oxides, titanium dioxide (TiO
2
) and zinc oxide (ZnO) are commonly used. It
was determined that nano-sized titanium dioxide and zinc oxide were more efficient at
absorbing and scattering UV radiation than the conventional size and were thus better able to
block UV . This is due to the fact that nano-particles have a larger surface area per unit mass
and volume than the conventional materials, leading to the increase of the effectiveness of
blocking UV radiation. For small particles, light scattering predominates at approximately one-
tenth of the wavelength of the scattered light.

Raleigh’s scattering theory stated that the scattering was strongly dependent upon

the wavelength, where the scattering was inversely proportional to the wavelength to the
fourth power. This theory predicts that in order to scatter UV radiation between 200 and 400
nm, the optimum particle size will be between 20 and 40 nm. UV-blocking treatment for cotton
fabrics was developed using the sol-gel method. A thin layer of titanium dioxide is formed on
the surface of the treated cotton fabric which provides excellent UV-protection; the effect can
be maintained after 50 home launderings. Apart from water droplet rolls titanium dioxide, zinc
oxide nanorods of 10 to 50 nm in length were applied to cotton fabric to provide UV
protection. According to the study of the UV-blocking effect, the fabric treated with zinc oxide
nanorods demonstrated an excellent UV protective factor (UPF) rating.



(a) (b)



Figure.6. (a) Normal fiber (b) Fiber treated with Tio
2






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(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

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Nano-Tex™ Resists Spills Fabric Protection Repel Ink
Inks and dyes contain concentrated amounts of quick-drying colorants. Fabrics treated with
NANO-TEX Resists Spills protection are not protected from these types of colorants but if
lifted quickly, stains can be minimized.

Figure.10. Nano-Tex™ Resists Spills Fabric Protection Resist Mud Stains
NANO-TEX Resists Spills fabric protection protects against both water-based and oil-based
liquids. Resists Spills fabric protection offers superior liquid repellency, which helps to
minimize stains. If the mud is sitting on the surface of the fabric, NANO-TEX fabric protection
will allow the wearer to carefully lift off the mud, therefore minimize staining. If the mud has
been ground into the NANO-TEX Resists Spills enhanced fabric, recommended garment care
cleaning tips should be followed to minimize or prevent the potential for staining. Mud stains
or thick oils that are smeared onto fabric may leave some residual staining.
5. Photocatalysis

When a semiconductor material is illuminated with ultra band gap light it
becomes a powerful redoxcatalyst capable of killing bacteria, cleaning water, and even
splitting water to give hydrogen and oxygen

5.2 Photocatalysis Reaction

i).Partial reactions

hv (UV) Ti0
2
e- + p (Exiton)
H0+p H0
Ti
4
Ti
3

Ti
3
[ Ti
4
O
2
abs]
[Ti
4
O
2
abs] + H

2
0 Ti
4
+ H0 + H0
2

ii).Overall reaction


H
2
0 + O
2
hv HO + HO

TiO

Titanium dioxide is a photo catalyst, once it is illuminated by light with energy higher
than its band gaps, the electrons in TiO
2
will jump from the valence band to the conduction
band and the electron (e-) and electric hole (h+) pairs will form on the surface of the
photocatalyst. The negative electrons and oxygen will combine into O
2
- the positive electric
holes and water will generate hydroxyl radicals. Since both are unstable chemical
substances, when the organic compound falls on the surface of the photocatalyst it will
combine with O
2
- and OH- respectively, and turn into carbon dioxide (CO

2
) and water (H
2
O).


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Through the reaction, the photocatalyst is able to decompose common organic
matters in the air such as odour molecules, bacteria and viruses. It was determined that a
fabric treated with nano-TiO
2
could provide effective protection against bacteria and the
discoloration of stains, due to the photocatalytic activity of nano-TiO
2
. On the other hand, zinc
oxide is also a photocatalyst, and the photocatalysis mechanism is similar to that of titanium
dioxide; only the band gap is different from titanium dioxide. Nano-ZnO provides effective
photocatalytic properties once it is illuminated by light, and so it is employed to impart anti-
bacterial properties to textiles.
6. Next Generation Finishing
6.1. Nano-Care
A technology that brings about an entirely carefree fabric with wrinkle resistant, shrink
proof, water and stain repellent properties, intended for use in cellulosic fibers such as cotton
and linen. It is a next-generation, ease-of-care, dimension-stabilizing finish, one step ahead of
methods that simply give wrinkle resistance and shrink-proofing. Nano-Care withstands more
than 50 home launderings. It imparts water repellency and stain resistance superior to those
of conventional methods, maintaining high water and oil repellency levels (80 and 4) even
after 20 home washes.

Features
• Superior Stain, Water and Oil Repellency
• Resists Wrinkles
• Breathable Fabric
• Preserves Original Hand
• Easy Care
6.2. Nano-Pel
This nanotech application of water-and-oil repellent finishing is effective for use in
natural fibers such as cotton, linen, wool and silk, as well as synthetics such as polyester,
nylon and acryl. Unsurpassed performance in durability and water and oil repellency may be
expected particularly with natural fibers. Nano-Pel cotton withstands 50 home launderings,
with functionality levels well-maintained for water and oil repellency (80 and 4) even after 20
washes (Figure shows Before & After).




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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.

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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.


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5. Yeo, S.Y., Lee, H.J., and Jeong, S.H., Preparation of nanocomposite fibers for permanent
antibacterial effect, Journal of Materials Science, 2003. 38: p. 2143-2147.

6. Draper D., Very little to it, World Sports Activewear, 2003. 19: p. 16-17.

7. Mills Andrew & Lee Soo-Keun, J - (Photochem Photobiol Chemistry), 2002.

8. Holme I, - (Textile Finishing), 2003

9. Derek Heywood - (Society of Dyers and Colourists, England) 2003.

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About the author:

K.G. Mythili - Department of Textile technology, PSG College of Technology,
Peelamedu, Coimbatore – 641 004.
Gopalakrishnan – I am
doing PG Diploma in Home Textile Management.i
did my Diploma in Textile Technology & B.Tech in Textile Technology from
PSG College of Technology & Polytechnic College. After my diploma I

worked as a Production & maintenance Supervisor in Cambodia Mills (NTC)
Coimbatore, after three years of experience I came back to my B.Tech.I did
17 paper presented in various technical symposiums, national & international
confrences in all over india and i participated in various technical workshops &
innovative project works. I published several articles in journals,magazines.
Area of Interest: innovative textiles, Technical textiles
Coimbatore-641 004, Email

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