ABSTRACT
Now a day’s people 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 headek to wash their garments. Also
military peoples have to survive in such drastic condition that they cannot
wash their cloths. Nanotechnology provides a new concept self cleaning textiles
which gives self cleaning as well as fresh cloths every day.
Water and soil repellency has been one
of the major targets for fiber and textile scientists and manufacturers for
centuries. Combinations of new materials for fiber production with a variety of
surface treatments have been developed to reach the condition of limited wet
ability. This paper gives the concept behind the self cleaning
textiles, different surface treatments based on nano technology, application
of self cleaning textiles problems and
limitations of self cleaning textiles.
INTRODUCTION:-
Finishes that repel water, oil
and dry dirt are important in all parts of the textile market – for clothing,
home and technical textiles. Water repellency is achieved using different
product groups, but oil repellency is attained only with fluorocarbon polymers.
They are modified to have a wide range of properties to fit the different demands
of the users and the intended purpose. This is one of the most interesting new
developments of chemical finishing.
The oldest repellent finish is
to repel water. The purpose of this finish is self evident. Drops of water
should not spread on the surface of the textile and should not wet the fabric.
The drops should stay on the surface and easily drip off. Similarly, oil
repellent finishes should prevent oily fluids from wetting treated textiles. In
a similar manner, soil-repellent finishes should protect textiles from both dry
and wet soils. In all cases, the air permeability of the finished fabric should
not be significantly reduced.
In addition to the desired
repellency effects, other undesirable fabric properties are often found with
repellent finishes. These include problems with static electricity, poor soil
removal in aqueous laundering, stiffer fabric hand, greying (soil redeposition)
during aqueous laundering and increased flammability. Some fabric properties
that are often improved by repellent finishes include better durable press properties,
more rapid drying and ironing, and increased resistance to acids, bases and
other chemicals.
Mechanisms of repellency
Repellent finishes achieve
their properties by reducing the free energy at fibre surfaces. If the adhesive
interactions between a fibre and a drop of liquid placed on the fibre are
greater than the internal cohesive interactions within the liquid, the drop
will spread. If the adhesive interactions between the fibre and the liquid are
less than the internal cohesive interactions within the liquid, the drop will
not spread. Surfaces that exhibit low interactions with liquids are referred to
as low energy surfaces. Their critical surface energy or surface tension γC
must be lower than the surface tension of the liquid γL (the internal cohesive
interaction) that is repelled. γL of water, at 73 mN m–1, is two to three times
greater than γL of oils (20– 35 mN m–1). Therefore, oil repellency finishes
with fluorocarbons (γC = 10–20 mN m–1) always achieve water repellency, but
fluorine-free products, for example silicones (γC = 24–30 mN m–1) will not
repel oil.7 Low energy surfaces also provide a measure of dry soil repellency
by preventing soil particles from strongly adhering to fibre surfaces. This low
interaction allows the soil particles to be easily dislodged and removed by
mechanical action.
WHAT
IS SELF CLEANING TEXTILES:
The self-cleaning fabrics have a
nano film coating of titanium dioxide nanoparticles which can break down dirt molecules,
pollutants, and microorganisms when exposed to visible and UV light. Clothes
made this way could be cleaned by simply exposing them to sunlight. Scientists
have developed a method for applying the thin film of titanium dioxide to
cotton easily and inexpensively. With their method, self-cleaning fabrics could
be produced commercially and for public use. The anothes method of
manufacturing self cleaning textiles is application of silver nano particals on
the besis of lotus leave surface structure.
The scientists note that self-cleaning fabrics could be especially
useful for people who don't have the time or means for washing their clothes,
such as military personnel or hikers
The
Lotus Effect: biomimetic ultraphobic surfaces
Biomimetics mimics naturally
occurring biological mechanisms with modification, to produce useful imitative
synthetic items using conventional methods available to science and technology.
The Lotus Effect has been named after the unusual properties of the leaf
surfaces of the lotus plant, which are remarkably water-repellent and
soil-repellent. The surface of the lotus leaf is covered by a thin
extracuticellular membrane termed the cuticle, which is covered by waxes
forming characteristic microstructures due to self-organisation. On smooth wax
layers (surface area contact 10%) the contact angle of water may reach 110°,
but because of the surface roughness of the wax layer, whose dimensions can be
measured in micrometres, a very pronounced super hydrophobicity is generated
with contact angles up to 170° and surface area contact as low as 7%. (As an
analogy, imagine a mercury droplet lying on a bed of nails or a pimple rubber
mat.) As a result, the area for adhesion of water is markedly diminished and
air is enclosed between the droplets and the wax crystals.
A similar situation holds true for
particles that are located on the surface of the lotus plant leaf. The contact
angle between the particle and the surface is minimised, which results in the
adhesion of particles to the water surface Independent of their size and chemical nature,
contaminants are removed from such optimised surfaces with only a small amount
of water.
This remarkable self-cleaning effect is
currently being harnessed to transfer the Lotus Effect into products with bio
mimetic self-cleaning surfaces. A façade paint suitable as an ‘anti-graffiti’
surface has already been devised and roof tiles and wood paints are currently
under development. It is conceivable that within the next decade the
application of the Lotus Effect using nanotechnology, precision engineered
polymers and suitable application methods could be used to provide a new
generation of fabrics with ultraphobic surfaces. These would undoubtedly be
expensive but would possess very high levels of water- and oil-repellency and
outstanding soil- and stain-repellency properties. However, the adhesion of
such polymers to the fibre surface and their durability to abrasion, wear,
laundering and dry-cleaning would have to be appropriate for the end-use.
Self
Cleaning Using Nano Technology:-
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, deodorant and anti-VOC
(volatile organic compounds) effects are possible when modifying the surface of
textiles before anchoring them on TiO2. Physical methods like
RF-plasma and vacuum-UV have been used to introduce carboxylic groups in
wool-polyamide5 and cotton6. The TiO2 forms a complex with the -COOH
groups retaining their oxidative action under solar irradiation in the presence
of water vapor and air. This leads to self-cleaning effects and to the
destruction of organic compounds like wine, coffee, make up, grease etc.
Chemical spacers have also been used to attach TiO2 to fabrics,
anchoring this semiconductor on one carboxyl and condensing the surface -TiOH
with the second carboxyl-group.
Dirt adheres to the fibers of most fabrics. To clean the
fabrics, people typically put them in the washer or send them to the dry
cleaners. But the water-repellency of fabrics made with the new coating is
superior and makes it easier to keep dirt from accumulating, because water that
is applied to the garment rolls off and takes the dirt with it. Suits made with
the new coating could simply be sprayed clean or wiped with a damp cloth to
remove the dirt, the researcher says. If desired, the fabric can still be
cleaned by conventional means, including washing as well as dry cleaning,
without harming the coating, he notes. In addition to suits, the new coating
could be applied to hospital garments, sportswear, military uniforms and rain
coats. Other possible applications include awning material for outdoor campers,
fabrics for lawn furniture and convertible tops for cars.
Application
of photo catalytic layer of titanium di oxide
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 organic
compounds (i.e. 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.
TiO2
is acts as photo catalyst layer which destructs the dirt particles photo
catalytically. The durability of this nano layer is very good up to 40-50
washing cycles. The simple process
sequence for applying the nano layer of Tio2 film is as
Pad dry cure
Working
of self cleaning photo catalytic layer:
The self-cleaning fabrics work using the
photocatalytic 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 organic compounds (i.e. 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.
Reactions
taking place during self cleaning:
Titanium dioxide is a photocatalyst;
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 (e–) and electric hole (h+) pairs will form on the surface of the
photocatalyst. 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. The following reactions show
the photo catalysis of the titanium di oxide treated fabric.
Application
of silver nano particals for self cleaning :
Application
of silver nano particles on textile surface is working as a phenomenon of lotus
leaf which does not absorb the water as well as do not adhere the organic
matter on its surface Similarly
silver nano particals can be applied on the surface of textile. These particals
canbe applied on the surface with plymer film (polyglycidyle methycrylate)
which ensures that silver nano particals are get fixed on textile surface.
These silver particals can be applied to silk, cotton, viscose etc. but the
concept is same as that of lotus plant. The nano particals are applied on to
the surface of textile by using simple finishing method pad-dry-cure. The following diagram shows applied nano particles
on the textile surface
Lotus leaf and a SEM image of its surface silver
nano particals applied on textile material
Working
of textile surface treated with silver nano particals :
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
nanowhiskers, 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.
Untreated
surface Treated
surface
The diagram shows that the two
textile surface one which is treated with silver nano particals and other is
not treated with silver nano particals.
The untreated
surface having dust particals, when water droplates rolls over it do not get
washed off because dust particals are adhere by textile surface. While treated
textile surface do not adheres the dust particals hnce when water particals
rolls over it dust get washed off. In fig. (b) Silver nano particals treated
surface shows self cleaning property.
Self cleaning textile in sport wear:
Muddy sports
kit, the bane of parents with active children, may be heading for the laundry.
Scientists have produced a coating that could make shirts and football shorts
self cleaning means which can either washed easily or do not allow to develop
the bacteria’s on fiber surface as shown in figure . The "self-cleaning" process makes
fabrics repel water, resist stains and even kill off the bacteria that grow in
sweat and make clothes smell. As a result, kit could be worn repeatedly between
washes, the distinctive aroma of kit bags gone for ever – even performance on
the field could be enhanced.
Scientists
working for the US Air Force have already produced T-shirts and underwear that
can be worn for weeks at a time without washing, and the technology has now
been licensed to a London company, Alexium, to develop for civilian
applications
Limitations of self cleaning fabric:
Breakthroughs in nanotechnology have made
self-cleaning fabrics both practical and economical. With commercial production
making the technology readily available to the masses, will washing machines
and laundry detergent become obsolete?
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 ideal.
It's also important to note that the newly developed method for producing
self-cleaning fabric has only been developed for cotton. Further research would be required to test
ways of applying titanium dioxide nanofilms to other textiles.
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.
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. Reduced
requirements regarding static properties by weight reduction at construction textiles
4. Fuel
savings through weight reduction in the field of transport
5. Improved
ageing behavior by extended surface purity effect.
REFRENCES
- A new dimension to textiles/garments -
Pradeep Kaira,
- http://www.snaimpex.com/a_new_dimension_to_textiles.htm.
- Hatch KL: Making a claim that a
garment is UV protective.
- AATCC Review,3, (2003),23-26.
- Development of New Textile Processing
Technology Based on Nano-
- Technology-Nano-Scale Coating Made
Possible on Monofilament Surface,
- http://www.toray.com/news/fiber/nr041022.html
- Selected Applications of
Nanotechnology in Textiles, Y. W. H. Wong, etal..AUTEX Research
Journal, Vol. 6, No 1, March 2006.
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