Nano-technology of manufacturing self-cleaning fabric.

1. Self-cleaning Fabric
Introduction
Water and soil repellency has been one of the major targets for fiber and textile
manufacturers for many days. Combinations of new materials for fiber production
with a variety of surface treatments have been developed to reach the condition of
limited wettability.
In nature an elegant approach found that combines chemistry and physics to create
super repellant surfaces as well as self-cleaning surfaces. Lotus leaves is the best
example of self-cleaning surfaces. The concept of self-cleaning textiles is based on
the lotus plant whose leaves are well-known for their ability to self-clean by
repelling water and dirt. More recently, botany and nanotechnology have united to
explore not only the beauty and cleanliness of the leaf, but also its lack of
contamination and bacteria, despite its dwelling in dirty ponds.
Basically, the lotus leaf has two levels of structure affecting this behavior micro-
scale bumps and nano-scale hair-like structures coupled with the leafs waxy
chemical composition. On the basis of lotus leaf concept scientist developed a new
concept self-cleaning textile that the textile surface which can be cleaned itself
without using any laundering action.
Now a days peoples are very busy in their work that they do not have time for
clean their daily wear cloths also people who are working in kitchens having
headache to wash their garments. Also military peoples have to survive in such
drastic condition that they cannot wash their cloths.
Technique of manufacturing self-cleaning fabric
The self-cleaning textiles can be manufactured by application of either
fluorocarbons or by nanotechnology.
By application of fluorocarbons
If the critical surface tension of solid is more than the surface tension of liquid,
then liquid will wet the solid. So if the critical surface tension of solid is reduced
than that of liquid, the water repellency can be achieved and this effect can be
imparted on fabric by using fluorocarbons, which are the carbon compounds
containing per-fluoronated carbon chain. They form thin film around the fibre and
as they possessa very low surface tension of around 10 dyne/cm, the drop does not
adhere to the surface of fibres.

2. Limitation of application of fluorocarbons:
 Good durability cannot be obtained for cotton.
 Fluorine compounds may cause skin related problems.
 Effect will reduce after few washes.
By application of nanotechnology
To overcome the limitations of application of fluorocarbons in developing self-
cleaning textiles new methods have been developed using nanotechnology. Nano
technology provides a new concept self-cleaning textiles which gives self-cleaning
as well as fresh cloths every day, this not only technically benefited but techno
economically also benefited.
Nanotechnology has real commercial potential for the textile industry. This is
mainly due to the fact that conventional methods used to impart different
properties to fabrics often do not lead to permanent effects and will lose their
functions after laundering or wearing. Nanotechnology can provide high durability
for fabrics, because nano-particles have a large surface area-to-volume ratio and
high surface energy, thus presenting better affinity for fabrics and leading to an
increase in durability of the function. In addition, a coating of nano-particles on
fabrics will not affect their breath ability or hand feel. Therefore, the interest in
using nanotechnologies in the textile industry is increasing.
There are basically two types of self-cleaning surfaces involving nanotechnology.
In the first place extremely water repellent, microscopically rough surfaces: dirt
particles can hardly get a hold on them and are, therefore, removed by rain or by a
simple rinse in water .The second example is given by photo-catalytic layers: due
to a layer of nanocrystalline titanium oxide, fouling organic material is destroyed
by solar irradiation.
Self-cleaning surface having a water contact angle greater than 150 degree and a
very low roll off angle. Water through these surfaces easily rolls off and
completely cleans the surface in the process. Self-cleaning fabrics not only resist
coffee and red wine stains but are also repellant to water, dirt, odor and are
antibacterial as well.
The manufacturing method of self-cleaning textiles using nanotechnology are:
 Using Photo catalyst
 Using microwaves
 Using carbon nanotubes
 Using Metal oxide colloidal
 Using silver nanoparticles
 Using chlorine halamine

3. Self- cleaning technique using photo catalyst
It is catalytic self-cleaning process. In this process Nano-sized titanium dioxide
and zinc oxide are used for imparting self-cleaning and anti-bacterial properties
.The fabric is coated with a thin layer of titanium dioxide particles heaving 20
nanometers diameter. Titanium dioxide is a photo-catalyst and when it is
illuminated by light of energy higher than its band gap, electrons in TiO2 will jump
from the valence band to the conduction band and the electron and electric hole
pairs will form on the surface of the photo-catalyst. The negative electrons and
oxygen will combine to form O2 radical ions, whereas the positive electric holes
and water will generate hydroxyl radicals (OH). Since both products are unstable
chemical entities, when the organic compound i.e. dirt, pollutants and micro-
organisms falls on the surface of the photo-catalyst it will combine with (O2-) and
(OH-) and turn into carbon dioxide (CO2) and water (H2O).Since the titanium
dioxide acts as a catalyst, so it is never used up. This is how the coating continues
breaking down stains over and over. Zinc oxide is also a photo-catalyst, and the
photo-catalysis mechanism is similar to that of titanium dioxide.
Figure: Photo-catalytic self-cleaning mechanism
The self-cleaning fabrics work using the photo-catalytic properties of titanium
dioxide compound used in many new nanotechnology solar cell applications. The
fabric is coated with a thin layer of titanium dioxide particles that measure only 20
nanometers in diameter. When this semi-conductive layer is exposed to light,
photons with energy equal to or greater than the band gap of the titanium dioxide
excite electrons up to the conduction band. The excited electrons within the crystal
structure react with oxygen atoms in the air, creating free-radical oxygen. These
oxygen atoms are powerful oxidizing agents, which can break down most carbon-
based compounds through oxidation-reduction reactions. In these reactions, the

4. organic compounds like as dirt, pollutants and micro-organisms are broken down
into substances such as carbon dioxide and water. Since the titanium dioxide only
acts as a catalyst to the reactions, it is never used up. This allows the coating to
continue breaking down stains over and over.
Figure: Working of self-cleaning textiles
Self- cleaning technique using microwaves
New technology attaches nanoparticles to clothing fibers using microwaves. Then,
chemicals that can repel water, oil and bacteria are directly bound to the
nanoparticles. These two elements combine to create a protective coating on the
fibers of the material. This coating both kills bacteria and forces liquids to bead
and run off. The same technology created by scientists working for the U.S. Air
Force, has already been used to create t-shirts and underwear that can be worn
hygienically for weeks without washing.

5. Self- cleaning technique using carbon nanotubes
Artificial lotus leaf structures were fabricated on textiles via the controlled
assembly of carbon nanotubes. Carbon nanotubes (CNTs) and surface modified
carbon nanotubes (PBA-g-CNTs) are used as building blocks to bio-mimic the
surface microstructures of lotus leaves at the nano-scale. Cotton fabrics, which
otherwise have perfect water absorb abilities, have been endowed with super-
hydrophobic properties water contact angles greater than 150 were measured. The
method provides a bionic route to create hydrophobic textiles. Furthermore,
considering the novel mechanical and electric properties of carbon nanotubes,
these carbon nanotubes coated cotton fabrics will find potential application in
sensing, conducting and special textiles.
Figure: Treated cotton fabric using carbon nanotubes.
Self- cleaning technique using metal oxide colloidal
The fabric is dipped and processed in metal oxide colloidal solution and then is
through heat treatment so as to make the fabrics with surface roughness on
nanometer scale. Then through water repellent treatment, the fabrics has surface
with water contact angle above 150 degree.
Self- cleaning technique using silver nanoparticles
A highly water-repellant coating made of silver nanoparticles that can be used to
produce suits and other clothing items that offer superior resistance to dirt as well
as water and require much less cleaning than conventional fabrics. Nano-Tex
improves the water-repellent property of fabrics by creating nano-whiskers, which
are made of hydrocarbons and have about 1/1000 of the size of a typical cotton
fiber. They are added to the fabric to create a peach fuzz effect without lowering
the strength of cotton.

6. (a)Untreated textile surface (b)Textile surface treated by
silver nano particles
The diagram shows that the two textile surface one which is treated with silver
nano particles and other is not treated with silver nano particles. The untreated
surface having dust particles, when water droplets rolls over it do not get washed
off because dust particles are adhere by textile surface. While treated textile
surface do not adheres the dust particles hence when water particles rolls over it
dust get washed off. In figure (b) Silver nano particles treated surface shows self-
cleaning property.
Self- cleaning technique using chlorine halamine
The technology works by attaching chlorine-containing molecules called
halamines to textile fibers. Chlorine in the form of halamines has powerful
bacteria-killing properties, used for example to disinfect swimming pools. Unlike
chlorine gas, there are no adverse effects since toxic chlorinated carbon atoms are
not generated. By sticking halamines to the cellulose fibers in cotton, the bacteria-
killing effect can be bonded to the material and used again and again. Eventually,
the chlorine is used up but can be regenerated with a wash in chlorine bleach. The
halamine-treated fabrics kill microorganisms almost instantly on contact, so these
materials are best suited for medical uses such as uniforms, wipes, bedding and
towels.
Photo catalytic degradation of odors compound
A photo-catalytic acrylic fiber SELFCLEAR yarn with higher-dimensional self-
cleaning properties which had been exclusive with conventional photo catalytic
fibers and started recently sailing their product for manufacture of clothing,
sportswear, uniforms, bedding, carpets and daily goods. Because titanium oxide is
applied into SELFCLEAR yarn, it has a higher self-cleaning activity with
deodorant, antibiotic and anti-soiling properties as well as excellent functional

7. stability, as compared to fabrics using a conventional photo catalytic reaction.
SELFCLEAR yarn has a multi-layer structure with micro voids tens of nanometers
in diameter on the surface of the acrylic fiber and that makes it a nanovoid
structure creating a greater surface area. Because of special nano-sized photo
catalytic titanium oxide, one-tenth the size of conventional titanium oxide used for
fibers, is used for SELFCLEAR yarn, it has a ten times greater surface With this
synergistic function of double nano-technology, it can produce excellent effects on
higher selfcleaning functions with deodorant, antibiotic and anti-soiling properties
compared to fibers using conventional photo-catalytic reactions.
Figure: Photo catalytic degradation of odorous component
Areas of application of application of self-cleaning fabric
 Hospital garments
 Sports wears
 Military uniform
 Upholstery
Limitations of self-cleaning fabric
Breakthroughs in nanotechnology have made self-cleaning fabrics both practical
and economical.
There are several factors limiting how quickly current self-cleaning fabric would
be able to break down organic compounds. Sunlight is the best source of light for
activating the self-cleaning process. A ketchup-stained shirt would have to be left
outside in the sun for at least a day in order to remove the stain. However, for
military persons or hikers, who are outside in the sun for long periods of time
without the time or means to clean their clothes, self-cleaning fabric would be

8. ideal. It's also important to note that the newly developed method for producing
self-cleaning fabric has only been developed for cotton.
Problems with self-cleaning fabric
The main reasons that self-cleaning fabrics require a lot of time to break down
stains is because titanium dioxide is very inefficient at using energy from sunlight.
The titanium dioxide serves as a catalyst for the break-down of dirt molecules by
providing electrons that oxidize oxygen molecules in the surrounding air. The
electrons are freed from the titanium dioxide via the photoelectric effect. But
because of titanium dioxide's high band gap energy, only high energy blue and UV
light photons have enough energy to excite electrons to the conduction band. High
energy blue and UV light only make up 3% of the solar spectrum, so titanium
dioxide can only use a very small portion of the sun's energy to break down stains.
Excitation of electrons to the conduction band is only the beginning of the cleaning
process. These electrons must then react with oxygen atoms, which then react with
the dirt particles. All of these reactions are limited by access to and the amount of
freed electrons in the titanium dioxide. So for a large stain, a lot of light energy is
needed before the fabric can fully break it down.
Conclusion
The realization of self-cleaning properties on textile surfaces by using the
nanotechnology includes a vast potential for the development of new materials or
new products and applications for known materials. The opening of new
application fields for textiles will lead to a new growth stage. For the growing
market of technical textiles a further increase in production volume, sales and
application fields can be expected by successful transfer of the self-cleaning effect
on textile materials. Structure based soil and water-repellent properties lead to an
efficient use of materials and are therefore in agreement with the principles of
sustainable development. The economic significance of the self-cleaning textiles
can be outlined as follows:
1. Ease of maintenance and environmental protection because of reduced
cleaning efforts
2. Time, material, energy reduction and consequently cost-efficiency during
production
3. Makes textiles longer-lasting
4. People need not to suffer from heavy laundry bills.
5. Improved ageing behavior by extended surface purity effect.