Nano Fibers: Productions And Its Applications

ABSTRACT:

The benefits to science and society from nano technology are substantial. It the critersion is to produce very minute particle size fibers and materials the nano technology is the only way to achieve the same. Nano technology is one of the rapidly growing scientific disciplines due to its enormous potential in creating noval materials that have advanced applications.

Nano fibers have high surface area to volume ratio, porosity so only we can applied in advance application such as filter medium, adsorption layed in protective clothing, face masks and etc..,Electro spinning has been found to be viable technique to produce nano fibers.

This paper reports on fabrication of nano fibers and its characteristics and high tech application in chemical protective clothing, drug delivery, tissue engineering and filter medium.

KEY WORDS: Drug delivery, Electro spinning, Fiber, Polymer, Nano fiber, Tissue Engineering

INTRODUCTION:

The term Nano in Nano technology comes from a Greek word Nanos which means dwarf. The dictionary meaning of dwarf is abnormally small.

One nanometer is one billionth of a meter or 10-9 meters. One Nano meters is about 100000 times smaller than the diameter of the human hair.

Unique properties of Nano materials have attracted not only scientist and research workers but also the businessmen, especially the textile, because of their high economical potential.

NANO TECHNOLOGY:

In 1974, Prof.Nario Taniguchi states Nano tech mainly consists of the processing of Separation, consolidation and deformation of materials by one atom or one molecule.

Nano tech is the design characterization production and application structures, devices and system by controlling shape & size at the nano scale.

This technology that can work at the Molecular level, atom by atom to create large structures with improved molecular organization.

Nano tech research efforts in textile have focused on 2 main areas

1) Upgrading existing functions and performance of textile materials
2)Developing intelligent textiles with completely new characteristics and functions

SYNTHESIS OF NANOPHASE MATERIALS:

There are 2 ways in synthesis of Nano phase materials they are:

Top down approach
Bottom up approach

Top down approach involving breaking down the bulk materials to nano sizes (Eg. Mechanical alloying)

Bottom up approach the nano particles also made by building atom by atom
(Eg. Inert gas condensation)

NANO FIBERS:

Nano science is used to create high strength, lightweight nano fibers with multifunctional properties. When referring to fibers nano is less than one micron and cant be seen without visual amplification.

While nano fibers have a diameter between 50-300 nm a cut off point is still debated, some belive that fibers up to 500 nm are called nano fibers.

In general, the nano fibers are taken to be the fibers between 100-500 nm in diameter. Fibers have nano scale diameters including high surface area to volume ratio film thinness, porous structure, lighter weight, desired level of modulus of elasticity and etc., These value added nano fibers used effectively in medicals, filters, liners for toxic chemical protective, protective fabrics, tissue scaffolds, drug delivery and many other advance applications.

PROPERTIES OF NANOFIBERS:

Nanofibers exhibit special properties mainly due to extremely high surface to weight ratio compared to conventional nonwoven. low density, large surface area to mass, high pore volume, and tight pore size make the nanofiber nonwoven appropriate for a wide range of filtration applications.

Figure shows how much smaller nanofibers are compared to a human hair, which is 50-150 m and figure 4 shows the size of a pollen particle compared to nanofibers. the elastic modulus of polymeric nanofibers of less than 350 nm is found to be 1.0 0.2 Gpa.

Techniques for synthesizing of nano phase materials are:

�Mechanical alloying
�Inert gas condensation
�Sol-gel technique
�Electro spinning method
�Plasma and laser processing spraying

Among these techniques electro-spinning techniques has been proved successfully for industrial production

PRODUCTION OF NANO FIBERS:

Several methods have been used and described in resent years to prepare Nano fibers
They are based different principle:

Drawing the fibers formed in a spinnerate by a stream of hot air is a method known as melt blown, which yields micro fibers of ca 1000-2000 nm
Dissolving polymer matrix of the islands-in-the-sea bi- component fibers yield s sub- micrometer in diameters fibers

Basically the nano fibers produced by three methods, they are detailed in the Table 1

POLYMER-SOLVENTS USED IN ELECTROSPINNING:

The polymer is usually dissolved in suitable solvent and spun from solution. Nanofibers in the range of 10-to 2000 nm diameter can be achieved by choosing the appropriate polymer solvent system [5]. Table 2 gives list of some of polymer solvent systems used in electrospinning.

ELECTRO SPINNING OF NANO FIBERS:

The Electro spinning technique can easily fabricate fictionalized nano fibers. This technique was invented in 1934, but there has not been wide spread research interest in this field till the mid 1990's

Electro spinning is unique approach using electrostatic forces to produce fibers. Fiber production using electrostatic forces have involved glare and attention due to its potential of forming fine fibers. Electro spun fibers have small pore size and high surface area. There is also evidence of sizable static charges in the electro spun fibers that could be effectively handled to produce three dimensional structures. The additional step to fabricate fictionalized nano fiber is the addition of function materials to the parent solution. It is to be remembered that the functional materials are added in to the nano fiber structure so that the products could have both the properties of nano fibers [porosity, high surface to volume ratio, diameter in nano scale and etc] and the functional properties of these doping materials.

The basic theory of nano fibers spinning process and the parameters affecting the process like, properties of polymer solution, thermal and mechanical properties of electro spun materials.

The apparatus used for electro spinning is simple in construction, which consists of high voltage electric source with positive or negative polarity, a syringe pump with capiliaries or tubes to carry the solutions from the syringe or pipette to the solution from the syringe or pipette to the spinneret and a conducting collector. The highly charged fibers are field directed towards the oppositively charged collector, which can be a flat surface or a rotating drum to collect the fibers. The shape is according to the requirements.

In the electro spinning process a high voltage is used to create an electrically charged stream of polymer solution or melt. A high voltage electrode is linked with the polymer solution. The solution is then spun thorough a capillary. Due to a 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 and create an interlinked fiber layer of the surface of collector.

Many types of polymers were processed into nano fibers of 50 to 1000 nanometers in diameter. Processing of polymer solutions is preferred to that of polymer melt as the high viscosity of melts does not allow forming sub-micrometer fibers. The problems linked with the use of toxic solvents required for majority of polymers is one of the obstacles in industrial production. An extremely low throughout rate 0.1 1 gram per hour and spinning is another one.

ELECTRO SPINNING OF CELLULOSE:

The technique of electro spinning cellulose of the nano scale involves the use of solvent. The cellulose is dissolved in the solvent; the liquid polymer solution is then squeezed through a tiny pinhole where a high voltage is applied. The technique relies of electrical rather than mechanical forces to form fibers.

The charge pulls the polymer solution through the air into tiny fibers, which is collected on an electrical group. The fiber produced is less than hundred nanometrers in diameter, which is thousand times smaller than in conventional spinning. This process made it possible to produce high performance materials from reclaimed cellulose materials. Thus there is much scope to recycle these materials at all phases of textile production and remove them form the waste stream.

TYPES OF NANO FIBERS:

NYLON NANOFIBERS:

Toray industries inc. has developed fibers with hydroscopic properties better than those of cotton. The fiber consists of extremely fine nylon measuring several tens of nanometers.

POLYESTER NANOFIBERS:

It is covered with a special film, which is tens of nanometrers thick. There is an increase in hydroscopic properties by of thirty.

LUMINESCENT POLYESTER:

It is covered with approximately 60 layers of nylon and polyester that have refractive indices for light. This creates a mystical hue that chanes according to both.

How light sticks the fabric
The angle from which the fabric is viewed.

Only reflecting light of a specific wavelength, the structure effectively brings out color.

CARBON NANOFIBERS

It is an ordered array of carbon atoms that can have tensile strength upto 50 times that of steel.

They have diameters of about 50-200nm and can be classified as:

Single walled carbon nanofibers /tubes they are single cylindrical structures.
Multi walled carbon nanofibers \ tubes they are formed of SWNTS covered with more of this kind of cylindrical structures.

APPLICATINON OF NANO FIBERS:

TISSUE ENGINEERING:

According to Langer and Vicanti, tissue engineering is an interdisciplinary field that applies the principles of engineering and the life sciences toward the development of biological substitutes that restore, maintain or improve tissue function. Natural tissue can be weakened or lost by injury, diseases etc. and therefore artificial supports are required to heal wounds and repair damaged tissues and decaying bone structure.

Recently the focus has shifted to adding cell adhesive molecules that would increase the cell attachment capacity of an engineered scaffold. A joint research by National University of Singapore and John Hopkins University of USA used first cell-adhesive molecules that are covalently attached to an electrospun scaffold. This research used poly (caprolactone-co-ethyl ethylene phosphate) (PCLEEP) copolymer in acetone (21.5 wt%) to fabricate PCLEEP nanofibrous mesh. The PCLEEP scaffold was then cleaned with 70% ethanol and then poly acrylic acid was grafted on to the scaffold surface by photo-polymerization process.

Casper et al have fictionalized polyethylene nanofiber with low molecular weight heparin by electrospinning process for its possible use in drug delivery, tissue engineering and wound repair applications.

DRUG DELIVERY AND NANOFIBERS:

There is a high potential for nanofibers to be a carrier of drugs to the specific sites. In order to incorporate drugs into the nanofiber matrix, a drug must be encapsulated into the nanofibrous structure. There is a few crucial parameters for drug delivery, such as burst release of drugs and the order of drugs release kinetics.

Release of tetracycline hydrochloride from electrospun PEVA [poly(ethylene-co-vinyl acetate)] PLA [poly(lactic acid)] and a 50:50 blend of these two has been explored by Kenawy. It has been found that the electrospun PEVA and 50:50 PLA and PEVA mats give the relative smooth release of drug over5days. Electrospinning was carried out using 14%(w/v) solution of PEVA, PLA and their 50:50 blend in chloroform. As tetracycline is not soluble in chloroform, it was solubilised in a small amount of methanol and added to the polymer solution. The resulting solution containing polymer and drug was then electrospun and collected on a rotating drum to produce a sheet of 100-200 m thickness. Release of he drug was monitored in pure water by UV-VIS followed by elemental analysis.

Magnetic particles are often used in the drug delivery carrier for tracking the drug carrier, and magnetite is a good candidate for this application. Nanocrystalline magnetite nanoparticles, having the diameter in the range of 5-10nm, have been incorporated into the nanofibers of poly (hydroxyethylmethacrylate) and poly VL-lactide using the electrospinning process. Tan prepared the aqueous solution of magnetic particles and used that with the polymeric solution to fabricate the super magnetic polymer nanofibers. Their result shows that the nanofibers containing upto 35% of magnetite particles demonstrate super-magnetism at room temperature.

CHEMICAL INDUSTRIES:

Polymeric nanofibers find applications in chemical and process industries in different areas such as catalysis, sensing, physical and chemical adsorption processes, etc

A catalyst is usually acceptable for large-scale application when it provides easy recycling and continuous operations without affecting the purity of products. There is a need for improving the catalytic efficiency and the stability of enzymes used in the processes so that these processes can compete with the traditional large-scale process. There is growing interest on metal nanoparticles and they hold real promise for their use in catalyses, chemical sensing etc. Lithium recently showed that the good particles could be selectively deposited on electrospun anatase nanofibers utilizing photo catalytic feature of Titania. This approach a simple route to fabricated metal-decorated titania nanofibers that have applications in catalysis and chemical sensing.

Recently nanofibers have been used as urea biosensors and gas sensors. Urease acts as a catalyst in the hydrolysis of urea to ammonia and carbondioxide and due to its specificity; urease can be used in urea detection. Nanocomposite fibers of urease and polyvinlpyrrolidone (PVP) were prepared using the electrospinning process by Sawicka. The immobilized enzyme maintained its reactivity within the nanofibrous structure and the membrane catalytically acted in different concentrations of urea solution.

Spinel lithium manganese oxide (LiMn2O4) and nickel cobaltite (NiCo2O4) well known as electrode material. In the electrospinning process with poly (vinyl) alcohol. They used calcinations technique in both cases and it has been reported that the calcinations temperature largely influenced the crystalline phase and morphology of the fibers. These materials are expected to improve the performance of electrolytic properties of the electrodes due to their high surface area. :

FILTERATION:

Polymeric nanofibers have been used in air filtration applications for more than a decade. Due to poor mechanical properties of thin nanowebs, they were laid over a substrate suitable enough to be made into a filtration medium. The small fiber diameters cause slip flows at fiber surfaces, causing an increase in the interception and inertial impaction efficiencies of these composite filter media .The enhanced filtration efficiency at the same pressure drop is possible with fibers having diameters less than 0.5 micron.

The potential for using nanofiber webs as a filtering medium is highly promising. Knowing that the essential properties of protective clothing are high moisture vapor transport, increased fabric breathability, and enhanced toxic chemical resistance; electrospun nanofiber membranes have been found to be good candidates for these applications. The highly porous electrospun membrane surfaces help in moisture vapor transmission. Gibson has analyzed the possibility of using thin nanofiber layers over the conventionally used nonwoven filtration media for protective clothing. Polyurethane and nylon 6 nanowebs were applied over open cell foams and carbon beads and tested for airflow resistance. They concluded that coating with the lightweight electrospun nanofibers could easily alter the airflow resistance, filtration efficiency, and pore sizes of nonwoven filter media. Doshi have evaluated composites of nanofibers with spun bond and melt blown fabrics for filtration characteristics. The nanofiber composite membranes have shown very high increase in the filtration efficiencies. Researchers at General Motors Company are working on nanofibers for different composite applications because of its scratch/wear resistance, low temperature ductility, low flammability, and recyclability.

NANO FIBERS IN PROTECTIVE CLOTHING

The non-woven fibers of Polyethylene-oxide (PEO), Polycarbonate (PC) and Polyurethane (PU) using different fiber charging methods like electrostatic spinning , corna charging and Tribocharging , and the infrared that the electrospun fibers have higher filtration efficiency than other non woven webs. PU and PC were found to have higher charge retention capacities than electrospun PEO fibers.

Thin nanofibers layers over the conventionally used nonwoven filtration media for protective clothing. Polyurethane and nylon 6 nanowebs were applied over open cell foams and carbon beads and then tested for airflow resistance. They concluded that the airflow resistance, filtration efficiency and the pore sizes of nonwoven filter media could be altered by coating with the lightweight electrospun nanofibers.

The best performance has been observed for POMs adsorbed on microporous carbons. It has also been observed that the POMs adsorbed onto nano magnesium oxide particles are more reactive than POM or nano magnesium oxide.

Nanocrystalline metal oxides have created a new opportunity for decontaminating hazardous substances. When the size of the metal oxides reaches nano scale, surface reactivity increases due to high surface area allows their use for the effective decontamination of chemical warfare agents and related toxic substances. Scientists are currently working of self-detoxifying nanofibers in which metal oxides are randomly dispersed on to the nanofiber matrices. They used Nanocrystalline magnesium oxide, which has been reported to react with organophosphorus compounds at room temperature by dissociative chemisorptions.

CARBON NANO TUBE-NANO FIBER COMPOSITES:

Singlewalled carbon nano tubes (SWCNT) And Multiwalled carbon nanotube (MWCNT) are at the center of attraction in nanotchnology due to their unique electronic and mechanical properties. As nanofibers or not strong enough by their strengths, nanotubes could be dispersed and aligned into nanofibers to develop stronger composites

Fabrication of electrospun poly (ethylene oxide) nanofiber embedded with (MWCNT) was successfully achieved by the electro spinning process. The dispersion of MWCNT in solution is highly required to have them aligned and separated into the nano fiber matrix, which was achieved in water by using amphiphiles. It has been seen from the transmission electron microscopy (TEM) images that most of the MWCNT�s were aligned along the fiber axis

OTHER APPLICATION

Electrical and optical application and other functional application like sensors. They are used in solar sails, light sails, and mirrors for use in space. Nanoconductors, nanoelectric applications as field effect transistors and ultra-small antennas.

CONCLUSION

The unique properties of nano materials have attracted nor only scientists and research workers but also the business, especially the textile, because of their huge economical potential to create, alter and impure the fiber at the molecular level and increase the durability and good performance beyond that of normal textile fibers. But 1990s onwards research the electro spinning of nano fibers have gained, due to the potential of nano fiber for use of different high tech applications.

The nano fibers that find applications in tissue engineering, drug delivery, protective clothing barrier materials and etc

A number of industrial applications of nanofibers will be developed in feature because nano fiber has good properties.

In feature, one can expect to see many more developments in textiles based on nano technology

REFERENCES:

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3.Seshadri Ramkumar and Mohammad Munin Hussain: Nano: The Next Wave In Nonwoven Textiles, Nonwoven Industry, April 2006.
4.Seshadri Ramkumar and Mohammad Munin Hussain: Functionalized nanofibres for advanced applications, Indian Journal of Fiber & Textile Research, March 2006.
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About Author:

Aravin Prince.P is final year student of B. Tech, Textile Technology, Department of Textile Technology, RVS College of Engg & Tech, Dindigul, Tamilnadu. He can be contacted at aravinprince@gmail.com