Nanotechnology has currently received an exceptional interest of researchers, technology incubators and commercial organisations in introducing materials having nanocomposite structure and new performance standards.
Atom is known to the world since the introduction of classical science age as an elementary unit of any material. However, the functioning of material was perceived in most cases in terms of aggregate structures. The recent onset of nanotechnology is demonstrating the material performance on the basis of very small particles that are having size range of fewer nanometers.
The word “nano” in nanotechnology has origin in Greek word “nanos” meaning dwarf (small). This prefix means one-billionth part, i.e. 10-9, for example, one nanometer is one-billionth part of a metre. How large is one nanometre! Perhaps it can be imagined by the diameter of single human hair which is approximately 100,000 times greater than one nanometer. Nanoparticles are atomic assembly that exhibits outstandingly different behaviour than the bulk of material.
An example may be seen in ceramics which are known as brittle and rigid materials. A ceramic material can be made deformable when their constituent grain size is reduced to low nanometer range. Also, a small amount of nanoparticles of a substance when included in a polymer matrix having similar size range, the resulting system exhibits an exceptional performance level.
Nanotechnologies can be perceived as the design, characterisation, production, and application of structures, devices, and systems by controlling shape and size of material particles on nanometer scale.
Why to see that magnificent change in the performance of material at nanoscale! This is the result of relatively significant increased surface area-to-mass ratio. The same material becomes more chemically reactive and exhibits different physical properties. Moreover, below the particle size of 50 nm, the laws of classical physics follow quantum effects that result in different optical, electrical and magnetic performance relative to the large size structure of the same material.
There is no single branch of science and technology/industry that is not affected by nanotechnology. The development and innovations in the next 10 years or so would even be showing stronger influence of nanotechnology on most materials. To date, it has accommodated the multiplication of applications in material manufacturing (more importantly in polymer modification and synthesis), and computer/electronic chips, medical diagnosis, health care, finishing formulations, energy, automations, biotechnology, packaging, space, aircrafts, protection and security.
The performance enhancement occurs when nanoparticles are introduced in a material i.e. making them the part of material structure; and this has changed the composition of several thermoplastic polymers for variety of applications. Nanocomposites that are currently used in polymers are based on nanoclays, carbon nanotubes (CNT), carbon nanoparticles and metal hydroxide. Nanocompsite fibers may be based on nonosize fillers/ particles including clay, metal oxides, carbon black, carbon nanotubes and graphite nanofibres.
Fibres and polymers/ plastics that can resist heat, chemicals, corrosion, fire, UV light, impact etc., are now possible with nanocomposites, both for consumer products and high performance applications.
Polymers reinforced with 2-5 wt% of nanoclays may exhibit significant improvement in thermal- mechanical properties, flame retardancy, barrier properties, dimensional stability, and modified electrical conductivity. An interesting example is seem in nylon-6 nanocomposite reinforced with 5 wt per cent of nanoclay resulting in 40 per cent increase in tensile strength, 68 per cent in tensile modulus, 60 per cent in flexural strength, and 126 per cent flexural modulus. The heat distortion temperature increases from 65 0C to 152 0C (5).
Being in nanometer size range, small amount of nanofillers possess high surface area. For example commercially a nanoclay product with surface area of 750 m2/gram (=an area corresponding to an equivalent area occupied by 9 soccer fields approximately) is known. Therefore, evenly distributed small amount of nanofiller may interfere with the polymer chain- its movement and reaction to external reagents and physical factors; and ultimately giving enhancement in the polymer toughness, strength and resistance to heat and chemicals.
Biological protective textiles can be produced using nanoparticle form of TiO2, and MgO. Photo- catalytic activity of Ti O2 and MgO can decompose harmful and toxic chemicals and biological agents. Textile finishing using nanoparticles can convert fabric into sensor- based materials.
Nanocarbons are nanosized carbon- based materials that can be bonded at molecular level of a material in various ways, producing unique properties in the material. The nanocarbon family may include carbon nanofiber, carbon black nanoparticles, fullerenes, carbon nanotubes etc.
Carbon nanofiber and carbon nanoparticles both may enhance the chemical resistance and electrical conductivity of composite fibers (1), apart from modifying the strength and toughness. Carbon nanotubes (CNT) consist of long, thin cylinder of carbon whose diameter (usually few nanometer) is significantly smaller than the length (several millimeter), therefore the length- to- diameter ratio (aspect ratio) is very high. CNTs are tiny shells of graphite rolled up in cylinder. These could be single walled (SWNT) or multi- walled (MWNT) and exhibit exceptional properties. The structure of multi- walled tubes is like cylinder inside other cylinder. The electronic, thermal, and structural properties of CNTs depend upon the length, diameter, and twist of the nanotube.. The properties exhibited by the CNTs are very interesting and an enormous volume of research is currently underway. For example their tensile strength is 100 times of steel at 1/6th weight. CNTs are studied in the domain of textiles to expand the applications of synthetic fibers including polyvinyl alcohol, polymethylmethacrylate, and polyacrylonitrile. However, there are several other application areas where CNTs are currently investigated to enhance the desired effects or to achieve multiple performance effects in devices. Such applications are in the nanometer-sized semiconductor devices, probes; sensors; conductive and high-strength specialist composites; devices for energy storage/ conversion; development of lubricants, coatings, catalysts; electro-optical devices, and medical applications.
The expansion in nanotechnology development may be imagined from the sales of emerging nanotechnology products that were 0.1 per cent of global manufacturing output in 2005, and estimated to reach 15 per cent by 2014. From 2010- onwards the presence of nanotechnology would be visible in most manufactured goods or high- end products Venture Capitalists had invested $ 1 billion in nanocompanies by the end of 2004.
In 2003, nanotechnology was generating $385 million annually in business in USA, and this volume is expected to reach $3.5 billion by 2008, and $20 billion by 2013. Chemical finishes, textile processing and finished textile products form an important area of nanotechnology. Synthetic fibers are gaining interest to modify for smarter applications using nanoclays (montmorillonite) and carbon nanotubes. However, the use of nanochemical finishes offers options to modify both natural and synthetic fibres.
Nanoclays are the viable source of modifying the fibres and polymers for a range of applications and are increasingly taking greater role in replacing undesired halogenated flame retardants for traditional and technical applications. The consumption of clay nanocopmosite, in 2005, accounted for almost one- quarter (24 per cent) of total nanocomposite consumption. The nanoclay composites are projected to raise their market share to 44 per cent by 2011. These figures clearly indicate the interest and importance of nanoclay composite.
The commercial viability of nanoclays is mainly credited to their reduced cost (around $ 2.25- $ 3.25 per pound), wider applicability to most synthetic polymers (PP, TPO, PET, PE, PS, polyamide), and performance enhancement produced in end- product.
More interestingly, Pakistan (Urals) has one of the five known regions of the world where natural reserves of montmorillonite clay exist; the other regions are in China (Tibet), USA (Utah), Ecuador (Peru), and Russia (Georgia). Montmorillonite clay is an extensively employed type of clay used in modifying the polymeric materials. Montmorillonite clay is a strong absorbent of minerals and heavy metals and prior the introduction of nanoclay composite it had been used for improving health including energy, stamina, smoother skin complexion, healing of bleeding gums, cavities, and wounds (10).
However, currently the production and ownership of nanoclays is held in industrialised regions. The local entrepreneurship may explore and develop a level of achievement in nanoclay composite at the cost of interest, investment and efforts. The presence of Higher Education Commission support in the form of University- industry research projects is also encouraging for nanoclay product development.
A comprehensive report on the opportunities in nanotechnologies had indicated that at nanoscale, chemistry, biology, electronics, physics, material science, and engineering start to converge and the distinction as to which property a particular discipline measures no longer applied. All these disciplines are contributing to the understanding of possibilities offered by nanotechnology.
We are surrounded with fiber- and polymer- based materials. From clothing to car, and from home to factory, the materials constituting physical environment consume significant volume and types of fibers and polymers. Nanocomposite polymers and fibers would increasingly become the part of our physical world exhibiting new performance standards. Primarily the nanotechnology is perceivable as the art of innovative advanced technology, however the producers and processors of traditional products in textile and polymer sector and the associated policy organisations in developing regions have much to accommodate to meet the opportunities and threats.
Like any other technology, there could be concerns on the health, environment and safety risks associated with the nanotechnology. The manufactured nanoparticles may enter the human body through various ways, and may possibly harm tissue or reach vital organs via the blood circulation. However, the risks shown by the nanoparticles in free state can not be the same when they are in bulk form for example nanocomposite materials or when the particles are in polymer structure. The precision of risks factors, if any, associated with nanoparticles are possibly in process to date by the regulatory assessment. Size effects are not addressed in the frame work of the new European Chemical Policy (REACH). Possibly such assessments for nanocomposites are the matter of time until more advanced studies are known.
However, the development and expansion in nanoparticles and nanocomposite are already going along several existing health and safety standards at work places, at least in industrialised countries, therefore it is unlikely that future would eliminate nanotechnology.