- 1 Introduction
- 2 Nano Materials
- 3 Nanofibers
- 4 Applications Of Nanofibers In Textile
- 5 Finishings
- 6 Electrospinning Nanofibers Can Turn Waste Into New Products
- 7 Future Of Nanotechnology In Textiles
Nanotechnology is an enabling technology that makes existing applications work better or more efficiently.
The future of technology at times becomes easier to predict. Computers will compute faster, materials will become stronger and medicine will cure more diseases.
The technology that works at the nanometers scale of molecules and atoms will be a large part of this future, enabling great improvements in all the fields of human presence.
Nanotechnology is concerned with positive control and processing technologies in the sub-nanometer range and so must play an essential roll in the fabrication of extremely precise and fine parts.
Nanotechnology is growing as a hot topic in the scientific field for many years. No other technology can compete with electrostatic spinning technique, which is used to produce very fine fibers with diameters less than 10 micrometers.
Here the article deals with purpose and technology of electrostatic spinning of nanofibers. This paper summarizes the recent development of nanotechnology in textile areas including Apparels, Industrial fabrics, Smart Textiles and Textile finishing.
Details on two major technical aspects, using nano size entities and employing specific techniques to create nanosize structure inside textile materials, have been elucidated.
A new concept of the textile surface coating has been introduced. At the end, perspectives regarding future development of nanotechnology for smart and intelligent textiles have been addressed.
The term nanotechnology comes from nanometer – a unit of measure of one billionth of a meter of length. It has been hailed as the biggest innovation since computer chips.
The prefix ‘nano’ is a Greek word meaning ‘dwarf’ denotes one-billionth part (10-9m) of the human hair. It can best be considered as a ‘catch-all’ description of activities at the level of atoms and molecules that have applications in the real world.
Nanotechnology, according to National Nanotechnology Initiative (NNI), is defined as the utilization of structures with at least one dimension of nanometer size for the construction of materials, devices or systems with novel or significantly improved properties due to their nano-size.
The leading countries in this technology are the US, Japan, and Europe. Ashima and Arvind are the first two Indian Textile companies to have bought the license to produce nanotechnology – driven clothes.
Approaches To Nanotechnology
There are two methods of manufacturing viz.
1) Top down.
2) Bottom up.
Today, there is considerable interest in what is called nanostructured material. Nanoparticles with the length of 1 to 100 mm exhibit new and improved properties compared to the corresponding bulk material.
Conventional materials have grain-sizes ranging from microns to several billion atoms each. Nanometer-sized grains contain only about 900 atoms each. As the grain size decreases, there is the significant increase in the volume fraction of grain boundaries or interfaces as shown in Figure.
This characteristic strongly influences the chemical and physical properties of the material. For example, nanostructured ceramics are tougher and stronger than the coarser grained ceramics. The market for nanoparticles will increase from US$493 mn in 2002 to US$900 mn in 2005.
There are several physical chemical methods for preparation of nanosized materials such as :
- Vapor phase reaction.
- Chemical vapor deposition.
- Inert gas condensation.
- Laser ablation.
- Plasma spraying.
- Spray conversion.
Nanotechnology In Textiles
The most interesting nanomaterials, which have potential applications in textiles, are nanocomposites, ie, composites carrying nanoparticles.
Extrusion of nylon with clay nanoparticles could lead to high-performance fire-retardant systems. The problem of dyeability of polypropylene could be solved if small quantities of nano clay were added to the polymer.
Several methods have been used and described in recent years to prepare nanofibers. They have based on different principles as.
- Drawing the fibers formed in a spinneret by the stream of hot air is a method known as melt-blown, which yields micro fibers of 1000-2000 nanometers.
- Dissolving polymers matrix of the Islands in the sea bicomponent fibers yields sub micrometers in diameters fibers.
- Electro Spinning.
The Electro-spinning method has been mostly patented and most important method for production of nanofibers. In this method, a high voltage is used to create and electrically charged stream of polymer solution or melt.
A high voltage electrode is linked with the polymer solution. The solution is then spun through a capillary.
Due to high voltage electric field between the tip of the capillary and a grounded collector, Taylor Cone is formed at the tip of capillary producing sub micron diameter fibers.
Fibers solidify as the polymer solvent evaporates and create an interlinked fiber layer on the surface of the collector.
Many types of polymers were processed into nanofibers of 50 to 1000 nanometers in diameter. Processing of polymer solution is preferred to that of polymer melt as the high viscosity of melts does not allow forming sub micron fibers.
In making the composite material, nanofibers play an important role. They have better mechanical properties than micro fibers of the same materials: this is caused by elongation in the electrostatic field by the lesser frequency of defects per unit length of nanofibers.
Nanofibers are novel synthetic fibers of unusually small diameter and good mechanical performance, produced by electrostatic.
Since these fibers have a high surface to volume ratio, they are susceptible to electrostatic charging, can be easily spun by this process. A typical nano fiber has the diameter between 50 and 300 nanometers.
Nanofiber is the finest fiber in the world with the diameter of about 100 nm. The size is 80000 times smaller than one strand of human hair.
Since their discovery in 1991, carbon nanotubes have generated intense research activity, because of their exceptional electronic and mechanical properties.
In the latter case, both theory and experiments have demonstrated that their elasticity and strength are extremely high.
Despite the enormous advances that have been made in the synthesis and purification of nanotubes within that last 10 years, processing nanotubes on macroscopic scales still remains a technical challenge, preventing the development of promising industrial applications (super-strong fiber actuators).
Carbon nanofibers are an ordered array of carbon atoms that can have tensile strength up to 50X that of steel. These tubes or fiver are often called graphite or carbon nanofibers as well nano tubes.
The technology for manufacturing carbon nano fiver is different from common fiber production techniques and the end uses are not those commonly associated with fibers.
The diameter of carbon nanofiber is 500-200mm and that of Single wall nano fiber (=1nm) and multi wall carbon nanofiber (2-5-nm).
According to the number of walls, carbon nanofibers are classified into single walled nanofibers and multiwall nanofibers. Single wall nanofibers are single cylindrical structures. Multiwall nanofibers can be through of the from Single wall nanofibers covered with more this kind of cylindrical structure.
Applications Of Nanofibers In Textile
Although nanofibers in textile cover small field of application but along with the normal textile material it has the pervasive field of application.
Textiles are becoming multifunctional thanks to nanofibers and electrostatic spinning so that textiles are now having applications apart from apparel use these are used in the high-performance technical textiles, biomedical textiles and how we can forget about eco-friendly textiles.
For instance in textile clothing such as in fire protective composites, in the high visibility garments, biodegradable nanofibers, defense clothing, etc.
“Scientists are figuring out how to organize polymer chain molecules-the basic stuff of textile fiber-for higher strength, higher melting points, and chemical and antibacterial impermeability”, for application as firefighter suit.
Applications Of Nanotechnology In Textile
- Industrial Fabrics.
- Smart Clothing.
- Shirts That Stop Bullets
At the Nanotech Institute at the University of Texas at Dallas, they have spun a new lightweight fiber that the scientists say is the toughest known.
Their new fiber is four times tougher than spider silk, and 17 times tougher than Kevlar, now used to make bulletproof vests.
The team’s key ingredient is tiny carbon nanotubes, miniscule rolled-up sheets of carbon atoms that can be found naturally in soot.
Carbon nanotubes are light and flexible, but enormously strong. They also conduct heat and electricity.
- Killer Clothing
“KILLER CLOTHING” which, as the name implies artificially enhances the properties of clothing to kill harmful agents on contact.
The technology, which some people likened to “nano daggers” is actually a chain of hydrogen atoms anchored by a nitrogen molecule that is then attached to the proteins in the fabric of the clothing.
The positive charge of the nitrogen atom acts to attract the negatively charged bacterial and fungal spores and cause them to impale themselves on the “dagger “of hydrogen atoms.
- Sports Equipment
The French tennis racket manufacturer has produced a racket with carbon nanotubes, which lead to an increased torsion and flex resistance.
Also, they are more rigid than current carbon rackets and pack more power. Long-lasting tennis balls are produced by coating the inner core with clay polymer nanocomposites.
These tennis balls lasts twice the lifetime of conventional balls.
Smart Materials And Nanotechnology
While synthesis of defect-free materials will lead to substantial improvements in performance, molecular nanotechnology will make more radical changes possible by integrating computers, sensors, and micro- and nano machines with materials. Here are some ideas:
- Pores fabric –
Micro pumps and flexible micro tubes could transport coolant or a heated medium to needed parts of clothing.
The kinds of sorting rotors shown in Figure 14 could be arrayed as “pores” in a semi-permeable membrane to allow only particular kinds of molecules through.
Water might be a useful molecule to select for, to keep one side of a fabric dry or another side wet. On the wet side, the water could be transported away to an evaporator, or stored.
- Programmable fabric
The basic idea is to have a material made of small cellular units that connect to each other with screws. Computers would direct the cells, powered with small electrostatic motors, to adjust their relative spacing with the screws.
The programmable material concept is not limited to fabrics but has many potential applications there. One example that Drexler pointed out would be a space suit that would allow nearly as much freedom of movement as one’s own skin.
Imbedded computers connected to strain gauges could sense the wearer’s intended movement and adjust the material accordingly.
Reflectance of the outer layer could be variable to absorb needed amounts of heat from the sun-facing side and transport it to cold spots—although the material’s insulative properties would allow very little of the wearer’s heat to escape.
Excess heat could be transported to radiators on the cold side.
- Robotic Fabrics
Fabrics could be self-cleaning: robotic devices similar to mites could periodically scour the fabric surfaces and integral conveyors could transport the dirt to a collection site, or the previously mentioned molecule-selective membrane could transport water to one side or the other for a cleaning rinse.
- Self-repairing fabrics
Fabrics could be self-repairing: sensors would detect discontinuities in the material via loss of signal or a reported strain overload and send robotic “crews” to repair the damage.
Self-shaping fabrics would be able to return to their original shape around a tear until repairs are affected.
- Smart Velcro
Large sections of fabrics could be made without visible seams by joining panels of fabric with microscopic mechanical couplings along their edges.
Similarly, surfaces could contain mechanical couplings that, when pressed together would bond with nearly the strength of the bulk material. This ‘smart Velcro’ could latch and unlatch at the user’s request.
Applications Of Nanotechnology To Industrial Fabrics
Objects made from the materials could be up to 100 times lighter, using 100 times less material.
As a result, ultra light cars, trucks, trains, and planes would use far less energy, especially with atomically smooth surfaces to reduce internal friction and air resistance losses.
With excellent properties, carbon would provide an excellent base for a heat resistant fabric as long as it is not in direct contact with strong carbide forming elements such as tungsten, titanium, tantalum, and zirconium at high temperatures.
The high axial thermal conductivity would act as a natural heat pipe to help to dissipate heat from hot spots on the material.
Thermal conductivity could be quite low in the transverse plane with an open array of molecules with long, widely spaced crosslinks.
Chemical Finishes And End Performance
Nanotechnology not only has exerted its influence in making versatile fiber composites but also had an impact in improving chemical finishes.
One of the trends in formulation processes is to pursue a nanoscale emulsification, through, even, and precise manner. These advanced finishes set up an unprecedented level of textile performances.
That imparts fabrics with stain-resistant, hydrophilic, anti static, wrinkle-resistant, and shrink proof properties.
NANO-TEX has recently launched several products that involved changing a fabric at the molecular level to create “NANO-WHISKERS”.
This has led to new and improved properties of breathability, stain resistance, water repellency and wrinkle resistance.
The whiskers make the fabric water resistant through surface tension, which is the force that causes water to form into drops or spheres, the shape having the least surface area.
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. So, the water remains on the top of the whiskers and above the surface of the fabric.
- Wicks body moisture
- Dries quickly.
- Breathable fabric.
Nanolayer Coating And Self-Repairing Function
Nanolayer coating is a new technology in textiles that is totally different from the traditional textile coating technology.
Nanolayer coating is based on the concept of SELF-ASSEMBLED MONOLAYERS (SAMS), in which chemical molecules form a single layer on the substrate with a depth of a nanometer.
Additional layers can be added each being a nanometer in depth. Besides coating thickness, evenness and denseness are the important characteristics of nano layer coating.
Nanolayer coating on textiles is also self-repairable. Once chemical molecules in the top coating layer are removed or displaced by an accidental force, the empty spot will soon be covered up because molecules simultaneously move back to the spot or the molecules move from the storage source within the nanolayer due to electrostatic neutralization.
This self-healing function of the nanolayer occurs through electrostatic effect
Nanocomposite Pp Dyeing
Clay nanoparticles or nano flakes are composed of several types of hydrous aluminosilicates. Clay nanoparticles
Clay nanoparticles are to introduce dye-attracting sites and creating dye- holding space in polypropylene fibers, known as nano-dryable fiber due to its structural compactness and lack of dye-attracting sites.
- To provide chemical and/or physical linkages to the dyes.
- To have thermal stability.
- To be stable in wet processing and other conditions.
Apart from modifying polymer structure and thermal/chemical stability, the nanoparticles will improve the mechanical property of the resultant material, the substantively of the nanocomposite to dyes and the performance of the final fiber produced.
Electrospinning Nanofibers Can Turn Waste Into New Products
The fiber produced is less than 100 nanometers in diameter, which is 1,000 times smaller than conventional spinning.
Thus this technique of electro spinning of spin nanofibers from cellulose soon is able to produce a low cost, high-value, high-strength fiber from a biodegradable and renewable waste product for air filtration.
Future Of Nanotechnology In Textiles
Future developments of nanotechnologies in textiles will have a two-fold focus.
- Upgrading existing functions and performances of textile materials
- Developing smart and intelligent textiles with unprecedented functions.
The latter is more urgent from the standpoint of homeland security and advancement of technology. The new functions with textiles to be developed include
- Wearable solar cell and energy storage.
- Sensors and information acquisition and transfer.
- Multiple and sophisticated protection and direction.
- Health-care and wound healing functions.
- Self-cleaning and repairing function.
Undoubtedly, nanotechnology holds an enormously promising future for textiles.
It is estimated that nanotechnology will bring about hundred billion dollars of market impact on new materials within a decade; textile certainly has an important share in this market.
We expect to see a new horizon of textile materials under this irresistible technology wave.
Nanotechnology-Working at a billionth of a nanometer scale-is a continuous source of new opportunities for the textile industry. “NANOTECH” can be described as a “SYNONYMS FOR INNOVATION”.
This is leading to technical fabrics with a wide variety of functions.
Nanotechnology will not only help the marketing of fabric and fashion because of its unique and incompatible properties but it is also a revolution for human beings just like the Internet wave.
Nanotechnology, with all its challenges and opportunities, is an unavoidable part of our future. The possibilities with nanotechnology are immense and numerous.
The researchers 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 ingenuity.
It can rightly be said that nanotechnology is slowly but steadily ushering in the next industrial revolution.
“Nanotechnology is an enabling technology that makes existing applications work better or more efficiently”
- Technical Textile International, Vol. 12, No. 2March 2003, p13-15
- AATCC REVIEW may 2004 “Nanotechnology in textiles” by Lei Qian, Institute of textile technology, North Carolina University.