These days, the word "nano"
seems to be popping up everywhere. Wall Street, Hollywood, and major
universities around the globe have all endeavored to associate their diverse
enterprises with this word. "Nano" is a metric unit that means one
billionth of a unit; as of late, it has been used most frequently in
reference to nanotechnology. The term "nanotechnology" has never
been used so broadly.
K Eric Drexler coined it in his 1986 book, Engines of Creation to refer to
his theories for molecular manufacturing, following up on visionary ideas
presented 27 years earlier by famed physicist, Richard Feynman. As the
possibilities of molecular nanotechnology grew and excitement built in the
scientific community many researchers began using the term for their own
endeavors at the nanoscale, unrelated to molecular manufacturing.
Nanotechnology seeks to provide and apply knowledge of the behaviour of
objects in the nanometre (nm) size range to the assembly of complex
structures for use in a variety of practical applications. The tiniest
substances promise to transform industry and create a huge market. In
chemicals, cosmetics, pharmaceuticals, technology and textiles, businesses
are researching and manufacturing products based on nanotechnology, which
uses bits of matter measured in billionths of a metre.
The technology, utilising materials a thousand times smaller than the width
of a human hair, is showing up in everything from auto parts to sunscreens
and clothing (1,2). However, nanotechnology has been used to
improve products that most of us use everyday. These include laundry
detergent, 6-pack rings, and surgical tools. One of the most widespread
applications of nanotechnology is in clothing. Nanotechnology is also called
a "bottom up" technology owing to using such small-scale building
units, in contrast to bulky material engineering that is considered a
"top down" approach (3). Many textile industries and
research organisation has already developed fabrics with distinguishing
properties. Scratch-and-sniff clothing is one example. Pleasantly scented,
tiny polymer beads are added to clothing, such as within a strawberry
applied on a shirt. Then there are menthol pajamas, scented to open the
nasal passages of people suffering from colds, ensuring a good night's
Some other type of clothing niche being explored on many fronts, with
perhaps more staying power than scratch-and-sniff shirts, involves the
nanoscale improvement of fabrics and fibres. Nanotechnology is adding its
labels to popular clothing brands with various products: Resists Spills,
Resists Static, Coolest Comfort, and Repels and Releases Stains. Researchers
all around the world are looking at all sorts of metal additives and polymer
additives, inorganic, organic materials to take them at nanoscale to impart
lots of interesting properties to textiles.
Preparation of nano-sized materials
There are several physico-chemical methods for preparation of nano-sized
material mentioned as below (4) :
Some commercially available nano-particles
Nano-particles may consist of various elements and compounds. The size of
the molecules is the sole criterion for inclusion in the category of nano-particles.
Nano-particles have a length of 1 to 100 nm. Conventional materials have
grain sizes ranging from microns to several millimeters and contain several
billions atoms each, nanometre sized grains contain only about 900 atoms,
exhibit new and improved properties compared to the corresponding bulk
material (Table1). Some nano-particles currently available are as follows (5-7):
Metals: Pd/Pt, Ag, Fe, etc.
Compounds: - Organic: Vitamins, DNA,
Hydroxylapatite, Colour pigments.
- Inorganic: TiO2, ZnO, Fe2O3, MgO, SiO2 etc.
Polymer: - cellulose nano-whiskers
- carbon nano-whiskers.
||Conductive magnetic properties, remote heating.
||ZnO and TiO2
||UV protection, fiber protection, oxidative
||TiO2 and MgO
||Chemical and biological protective performance,
provide self-sterilizing function.
or Al2O3 Nano-particles with PP or PE
||Super water repellent finishing.
||Indium-tin oxide Nano-Particles
||EM / IR protective clothing.
||Increasing resistance to abrasion.
||Carbon black Nano-Particles
||Increasing resistance to abrasion, chemical
resistance and impart electrical conductivity, colouration of some
||High electrical, heat and chemical resistance.
||Wrinkle resistance, stain resistance, and water
Table 1 Nano-particles and
potential textile applications
Metals and metal oxides nano-particles
Nano-size particles of Pd/Pt, Ag and Fe can be applied on textiles to impart
antibacterial, conductive magnetic properties and remote heating properties.
Silver has been used for the treatment of medical ailments for over 100
years due to its natural anti-bacterial and anti-fungal properties. Nano-silver
particles are widely applied in socks to prohibit the growth of bacterial.
In addition, nano-silver can be applied to a range of other healthcare
products such as dressings for burns, scald, and skin donor and recipient
Nano-silver particles can be applied on textiles by padding method with good
laundering durability (8). Hoon Joo Lee and Song Hoon Jeong (9)
have reported that nano-sized silver colloids and nano-silver treated
polyester nonwovens have good bacteriostasis. Water based and ethanol based
nano-silver colloids with spherical nano-particals of diameter 2-5 nm can be
applied to polyester nonwoven fabric. It has been reported that the growth
of bacteria colonies is absolutely inhibited with only 10 ppm colloidal
Nano-size particles of TiO2, ZnO, Al2O3,
and MgO are a group of metal oxide that possesses photo catalytic ability,
electrical conductivity, UV absorption, and photo-oxidising capacity against
chemical and biological species. Intensive research involving the nono-particles
of metal oxides have been focusing on antimicrobial, self decontaminating,
and UV blocking functions for both military protection gears and civilian
health products. Nylon fibre filled with ZnO nano-particles can provide UV
shielding function and reducing static electricity of nylon fibre. A
composite fibre with nano-particles of TiO2/MgO can provide self-sterilising
TiO2 and MgO nano-particles can be entrapped into a textile
fibres during the spinning process or incorporated into a textile material
via normal textile finishing methods with a resultant material having
chemical and biological protective performance (11).Cellulose
fibre filled with nano-particles of metal oxides (such as TiO2)
from in situ synthesis can be used as a catalyst in fuel cells (12).
Polymer and polymer nano-composites
It has been established in recent years that polymer-based composites
reinforced with a small percentage of strong fillers can significantly
improve the mechanical, thermal and barrier properties of the pure polymer
matrix. Moreover, these improvements are achieved through conventional
processing techniques without any detrimental effects on processability,
appearance, density and aging performance of the matrix. Now-a-day's hybrid
polymers (such as Organoallcoxy silanes), which are the hybrid structure of
inorganic-organic nano-composite materials are being used to impart the
combination of scatch resistance with dirt-repellent effect, high
transparency, special barrier properties or antimicrobial function to the
Clay nano-particles: Clay basically consists of hydrous
aluminosilicate and is low in density. Nanosize clay particles or flaks can
impart excellent flame retardant functionality to the textile due to the
heat resistant behaviour of the nanoclay (14). UV blocking power
and outstanding barrier functionality are due to the internees of nanoclay
to corrosive chemicals and its neatly layers configuration inside fibre (15,16).
In terms of mechanical attributes, nylon6 clay composite with a clay mask
fraction of 5% shows 40% higher tensile strength, 68% greater tensile
modulus, 60% higher flexural strength, and 126% greater flexural modulus.
Such a significant improvements in composite strength even leads to
application of nano clay filler as a protective insert in infantry helmets (15,16).
Nano clay fillers modified with quaternary ammonium salt have been
introduced into polypropylene fibre, the resultant fibre can be coloured by
acid and disperse dyes to 1-4% colour shades for incorporation of less than
5% nano-dry fillers. The modified nano clay introduces dye attaching sites
to the polypropylene fibre generates void space inside the fibre to entrap
dyes without degrading the beneficial properties of polypropylene (17).
Carbon nano particles: Carbon nano black particles are extremely
effective reinforcing material for composite fibres (10). With
their high aspect ratio, carbon black nano particles can improve abrasion
resistance and hence increase the durability of composite fibres. Carbon
black nano particles can also result in high chemical resistance and
electric conductivity after they are mixed with fibre polymer matrix.
Polyester, nylon and polypropylene have been used as polymer matrix with
weight percentage of nano size filler range from 5% to 20% (18,19).
Dapeng Li and Gang Sun (20) have reported that carbon black nano-particles
can directly be used in traditional dyeing processes to dye polyester and
acrylic fabrics. Polyester and acrylic fabric were dyed with nano carbon
black particles using a dip-pad, dry and cure technique. Effective
colouration of these fabrics has been reported with 8 nm particles, using
cationic dispersing agent, at 1800C treatment temperature.
Polymer nano-whiskers: Nano-whiskers, each of which is just 10
nanometres long (a grain of sand is 1 lakh nanometres in comparison).
Basically, nano whiskers, 1/1000 the size of a typical cotton fibre are
attached to the individual, constituent fibres of the fabric. The whiskers
are hydrocarbons added by dipping in an aqueous solution 8. The whiskers
modify water-resistance of fabric due to surface tension that causes water
to form into drops or spheres. The spaces between the whiskers on the fabric
are smaller than a typical drop of water while the whiskers are hydrophobic
and do not absorb water. As a result, water remains on top of the whiskers
and above the surface of the fabric.
Another similar product is nanosphere that makes fabric water and
soil-resistant. In his work Soane (2) immersed the cotton fabric
in a pool containing a mixture of water and billions of these nanowhiskers,
then heated the pool in order to evaporate the water and cause the
nanowhiskers to chemically bond to the cotton's cylindrical fibres, coating
each thread entirely.
Cotton fibres, primarily composed of cellulose (Figure 1), owe their high
degree of absorbency to the many The stain-repellent fabrics from Nano-Tex,
incorporate billions of tiny fibres, each about to nanometres (that's
0.0000004 inches) long, that are embedded within traditional cotton or
linen. The waterproof fibres, which Nano-Tex calls "nanowhiskers,"
make the fabric dense, increasing the surface tension so drops of liquid
can't soak through-just like raindrops on a freshly waxed car.
The company says this Nano-Care treatment will withstand 50 home launderings
before its effectiveness is lost. These may be due to the negatively
charged, hydrophilic hydroxyl groups that lie along the naturally occurring
polymer's carbohydrate structure. The outer-shell electrons of the carbon
atoms from which the whiskers are constructed form nonpolar covalent bonds
and therefore do not readily bind to polar water molecules.
Thus, the attachment of the carbon whiskers to the cotton fibres permanently
alters the physical properties of the cotton by changing the fibres from
hydrophilic to hydrophobic. Because the nanowhiskers are so small, they are
able to permeate the cotton fabric and attach to each thread without
modifying the appearance or feel of the pants. The ability to engineer
effective nanostructures such as these owes its many promising applications
to the enduring maturation of nanoscience.
In another study the cotton nanocomposites, fibre modified with organo
clays, have been developed to improve the thermal properties of cotton with
minimal impact on other desirable properties (21). A method of
laboratory scale wet spinning and nonwoven production has been developed;
regenerated cellulose nanocomposite fibres have been produced by a wet
spinning technique that is a modification of the Lyocell method for
producing regenerated cellulose commercially. The nanocomposite fibres were
processed into nonwoven substrates using small-scale paper production
equipment. Thermal analysis revealed that the nonwoven production process
does not hinder the improvements in thermal behaviour seen in earlier tests
on fibres. Moisture regains analysis showed that the water uptake of these
materials is comparable to that of unprocessed cotton.
In another work, carbon nanowhiskers and carbon nanotubes were doped with
two types of polymer precursors were used; linear low density polyethylene
and nylon-6. The fillers in each case were carbon nanowhiskers and
multi-walled carbon nanotubes. It has been reported that the improvement
with carbon nanowhiskers was around 17% while it increased to 34% with MWCNT.
Out of the four systems (two fillers and two polymers) investigated, the
system with Nylon-6 infused with MWCNT yielded the most promising results.
Tension tests on individual filament of this system showed about 150-300%
improvement in strength and stiffness with 1% MWCNT loading. TEM studies
revealed that extrusion technique caused sufficient alignment of MWCNT along
the length of the filament, which may have caused the gain in mechanical
The former involves separation of nano-whiskers from cellulose fibres,
proper treatment and embedment into polymers. It has been found that these
nano-whiskers have twice the strength of conventional glass fibres. The
embedment of graphene layers into polymers has its own advantages. Apart
from high modulus, electrically conductive graphene layers enable proper
orientation (by applying known voltage) of the graphene layers in the
polymer during manufacturing thereby increasing the reinforcement effect and
hence the enhancement of many properties.
Nano-whiskers are wonder molecules, which can impart various functional
properties not only to the textiles but also contribute significantly in the
field of electronics and medicine. Recently several works has been reported,
where nano-whiskers have been synthesised from a variety of materials by
using some new and improved techniques.
Nano-particles in functional textile finishing
In some typical textile finishing applications nano-particles can
substantially alter surface properties and also confer different functions
to the textile materials (22,23). The nano size particles offer a
larger surface area compared to bigger particles. Being in the nanometre
range, the particles are transparent, so they do not blur colour or alter
brightness of textile substrates.
Nano-particles can be applied on textiles by two-stage process. Initially,
there is the manufacture of new, stable nano-material, which must in the
first instance be protected against properties defined by the size of the
particles. The second step sees the creation of the foils, emulsions and
dispersions that can be applied to the final textile product, in the most
favourable case, by means of conventional finishing processes.
Nano particles are most commonly applied to textiles by coating using a
composition of nano particles, a surfactant, ingredients and a carrier
medium. Coating techniques, which modify the surface of the textile,
Spraying: the coating composition is
sprayed on to textiles, with control of the depth and targeting to
Dipping and soaking in an immersion
container followed by a drying step.
Transfer printing such as rotary,
flexography and inkjet printing.
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.
Nano particles have large surface area
to volume ratio, which makes it easy for them to attach to fibre or fabrics,
and increase the durability of the functions imparted by the particles. In
addition, the coating of nano particles does not affect the breathability,
and hand feel of the textile. The commonest functions are wrinkle
resistance, stain, soil and water repellency and anti static, anti bacterial
and anti ultraviolet protection (8).
Wrinkle resistance: Wrinkling occurs when the fibre is severally
creased. When fibre or fabric is bent, hydrogen bonds between the molecular
chains in the amorphous regions break and allow the chains to slip past one
another. The bonds, reform in new places and fibre or fabric is held in the
creased configurations. The disadvantages of conventional resin applications
include decrease in the strength of fibre and in abrasion resistance, water
absorbency and dyeability, as well as in as in breathability.
Stain resistance: Staining of fabrics occurs from re-deposition of
soil during laundering or dry cleaning, deposition of dry soil from the air
or contact with foreign matter. Silicon chemicals and fluorochemical
finishes can be used to confirm resistance to soil, water and even oily
stains. The stain-repellent fabrics from Nano-Tex (Figure 2), incorporate
billions of tiny fibres, each about to nanometres (that's 0.0000004 inches)
long, that are embedded within traditional cotton or linen. The waterproof
fibres, which Nano-Tex calls "nanowhiskers," make the fabric
dense, increasing the surface tension so drops of liquid can't soak
through-just like raindrops on a freshly waxed car. The company says this
Nano-Care treatment will withstand 50 home launderings before its
effectiveness is lost.
The most developed nanotechnology application for textiles is currently in
the areas of stain, oil, and water repellency; stain release and wrinkle
resistance. Stain resistance, stain repellent, and dual action repel and
release finishes all can be applied by using nanotechnology.
Repellent products lower the critical surface tension of the fabric so the
fabric does not attract stains or soil. Oil and water bead up and roll off
the fabric. When a repellent finish is applied to fabrics, the invisible
repellent finish provides superior water/oil repellency and protection
against spills and stains.
Stain release products allow for stains and spills to soak into the fabric;
oil and water may bead slightly and stains are applied, the fabric will be
slightly oil/water repellent, but the invisible stain release finish allows
for ground in stains to be easily removed during laundering. This finish
with the addition of a water-loving component allows absorbed stains to wash
out and easily removed with home laundering. When a stain release finish is
Dual-action repel and release is the newest finish in the industry. The
finish combines advantages of both stain release and repellent finishes into
one. This twofold protection offers a unique balance of repellency that
works in tandem with an advanced stain release, which helps to liberate the
toughest stains including tough ground-in stains. With dual-action repel and
release finishes, consumers get twice the stain protection in one
Water repellency: Water repellant finishes modify the surface of
fibre and do not block the interstices. Hence fabric permits air and water
vapour to pass through. Early water repellant coatings were easily removed
dry cleaning or laundering. Nowadays, wax emulsions, pyridinium compounds,
N-methylol compounds, silicons and fluoro chemicals are used to impart water
repellency to various natural and synthetic fibres.
To improve the properties of wrinkle resistance, stain resistance and water
repellency recently several products have been introduced. Nano Whisker
introduced by Nano-tex is one of the best options. They are attached to the
fabric permanently, unlike the topical coatings or bulky laminated fabrics
that have traditionally been used for this purpose. The whiskers are
hydrocarbons added to the fibres in an aqueous solution. The changes to the
fibres do not affect the natural hand feel and breathability of the fabric.
The fabric shows very good wrinkle resistance, the processing is
undetectable and a " peach fuzz" effect has been reported. The
finish can be applied onto textiles through a nanoscale emulsification
process in a more thorough, even, and precise manner than traditional
In the case of fabric, rolls of woven cotton fabric from textile mills are
immersed in liquids containing trillions of nanowhiskers they are waterproof
and increase the density of the fabric. Then this treated cotton, is dried
in ovens binding the tiny fibres to the comparatively much larger cotton
threads. This increases the surface tension on the outer layer of the fabric
so liquid cannot soak through.
Though the final product looks unchanged, it provides a nearly solid barrier
to liquid or wrinkles, for instance. Nanowhiskers provides an even
application and does not change the surface properties unlike traditional
finishes. Nano-particles are extremely tiny and therefore the addition of
these particles on fabric is not detectable by hand.
Nano-particles added on textile materials cannot be detected by the naked
eye; therefore the original colour of the products will not be altered. Nano-particles
form a protective layer on the face of textile materials instead of changing
their chemical properties; therefore they give no hazardous substances and
have no side effects. Textile products, which have been processed with nano-particles,
are more durable than the traditional finishes with repeated washing.
Nano-finishes can add additional functionality to fabrics such combination
of wrinkle and stain repellency in one application. But on the other hand,
Nano-tech garments could under perform if proper care is not taken. Proper
care for these garments includes the use of delicate machine washes and drip
dying, no dry-cleaning and avoiding the use of chlorine bleach and wringing
of the clothes.
Anti static performance: Static usually builds up in synthetic fibres
such as in nylon and polyester because they absorb little water.
Conventionally surfactants are used to spread the small amount of moisture
on the surface of fibre so as to pose the charge to leak away. One of the
best electrically conductive nano particles is silver. Silver nano particle
helps to dissipate the static charge effectively.
Anti bacterial effect: The commonly used anti bacterial agent was
quaternary ammonium compounds. Many chlorinated organic compounds and organo
metallic compounds containing copper, silver, iron, manganese or zinc also
make fabrics resist growth of bacteria. The use of nano silver particle
offers durable anti-bacterial finishing to the textile.
Ultra violet protection: To impart UV protection, several nano
compounds or nano particles can be applied on textile material. The
commonest nano compounds used are titanium dioxide and zinc oxide of nano
size. They provide a protective benefit by reflecting, scattering or
absorbing harmful UV.
At present several research organisations and industries are offering
nanotechology and its application techniques for textiles. Some of them are
Nano-Tex, LLC, Greensbara, NC, USA.
Texcote Technology (International)
Schoeller Textiles AG, Switzerland.
Beiging Zhong-Shong Century
Nanotechnology Co Ltd, China.
Testing and analysis of nano-materials
The morphological features of nano material and structures need to be
determined in various stages of production such as size distribution,
porosity, pore size distribution, surface structure and composition, which
are critical to ensure the materials and structures are in nano scale to
archive special properties (24-26). Such structural feature can
be characterised by a rang of techniques and instruments such as Particle
Analyser, Atomic Force Microscopy (AFM), Scanning Tunneling Microscopy (STM),
Scanning Electron Microscopy (SEM), High Resolution Transmission Electron
Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), Auger Electron
Spectroscopy (AES), Near Field Scanning Optical Microscopy (NSOM or SNOM),
X-ray and Neutron Diffraction or other spectroscopic techniques.
The properties of nano materials and structures/composites also need to be
measured to test whether specific and unique properties can be derived due
to the nano scale structures. Properties characterisation should be carried
out in various aspects in relation to specific functions to be achieved such
as in physics, mechanical, electrochemical, optical and thermal properties.
Examples of propertie's characterisation techniques: property to be
characterised techniques; Dynamic Time Resolved Techniques; Magnetic
Scanning Electron Microscopy with Polarisation Analysis (SEMPA); Surface
Magnet - Optic Kert Effect (SMOKE) Spectroscopy; Spin-Polarised Low -Energy
Electron Microscopy (SPLEEM); Magnetic Force Microscopy (MFM);
Electrochemical Impedance Spectroscopy; Potential Sweep Method;
Electrochemical Quartz Crystal Microbalance, Mechanical Electricity Method;
Vibrating Reed Method; Thermal Diffractional Scanning Colorimeter(DSC).
Finally, functional performances of final products need to be characterised
to test the roles and impact of nano materials and nano scale structures.
Only when new and/or significantly enhanced properties are introduced, due
to the nano scale sizes or structures, can nano-products be claimed, based
on the definition of nanotechnolgy.
Economical and environmental aspects
The unique properties of nanomaterials have attracted not only
scientists and research workers but also businesses, because of their huge
economic potential. The national science foundation reports that nano-related
goods and services will increase to a US$ 1 trillion market by 2015. This
amount is larger than the combined businesses of the telecommunications and
information technology industries. Several hundred billion Euros are
forecast to be created by nanotechnology in the next decade (24).
The nano materials markets could expand to US$ 4 billion by 2007. It was
believed that 2 million new employment opportunities would be created in
order to meet the worldwide annual production demand of US$ 1 trillion in
Nanotechnology may impart favourably on the environment as well. By using
less resource without sacrificing performance, nanotechnology may save raw
materials and also upgrade quality of life.
The development in the applications of nano-particles, nano-composites
and nano-sphere has been very rapid in past years, particularly in the field
of textile finishing. These nano-size materials are able to enhance the
physical properties of conventional textiles in areas such as anti-microbial
properties, water-repellency, soil-resistance, anti-static, anti-infrared
and flam retardant properties, dyeability, and strength of textile
materials. In future the application of these wonder nano-particles can be
extended to produce textiles with health-care and wound healing functions as
well as self-cleaning and repairing functions.
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Note: For detailed version of this
article please refer the print version of The Indian Textile Journal
December 2007 issue.
B H Patel
Department of Textile Chemistry,
Faculty of Technology & Engineering,
The M S University of Baroda, Vadodara 390001.
Dr D P Chattopadhyay
Department of Textile Chemistry,
Faculty of Technology & Engineering,
The M S University of Baroda, Vadodara 390001.