Commercial Standards of Industrial Nanofiber Production, Research Paper Example
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Nanotechnology involves the synthesis and research of nanoscale materials, such as nanofibers. Electrospinning is one method that scientists are currently researching and conducting in order to fabricate nanofibers. There are currently hundreds of laboratories conducting research on electrospinning and nanofiber production. (Petrik and Maly) Electrospinning involves the uniaxial stretching of a vicoelastic solution at a high voltage. (Afanasov et al.) Different polymers, oxides and metal fibers can also be made through electrospinning. “However, what makes electrospinning different from the other techniques – it is the most productive method in nanofiber and nanofiber assemblies’ fabrication, which as well give the rise to manufacturer’s interest to the method (Afanasov et al.)”. Nanofiber fabrication is ideal for the commercial market in developing new composite materials to combine with the usual nonwoven material. There are new markets for nanofibers in air filtration, liquid filters, and biomedical applications, such as wound care, skin scaffolds, bone scaffolds, vessel scaffolds and drug delivery systems. In addition, inorganic/ceramic nanofibers are used for energy generation and storage. (Petrik and Maly)
The size of global technical textile industryhas been estimated to increase from $5.29 billion in 2006-2007 to $10.6 billion in 2011-12 per the Working Group for the Eleventh Five Year Plan. (CCI, 2010) The global market for microfiltration membrane products was estimated at $1.2 billion in 2010 and is expected to have an annual growth rate of 8% each year, reaching $1.8 billion in 2015. (BCC, 2006)
There are specific properties of nanofibers that make them viable for the global technical textile industry. In addition, nanofibers can be used for a broad range of both medical and consumer products. The specific properties in which nanofibers exhibit include a high surface to weight ratio, low density, increased surface area compared to mass, high pore volume and tight pore size (Hedge et al., 2005). Hedge et al., 2005 compares a nanofiber to human hair and a pollen particle, which is 50-150 µm; whereas, the elastic modulus of a polymeric nanofiber is found at 350 nm.As mentioned previously, the nanofibers are used for numerous applications. For instance, nanofibers function in filtration devices and protective clothing when combined with other nonwoven products. In addition, electrospun fibers function in gas turbines, compressors and generators. Furthermore, they are used in the medical field for drug delivery devices and artificial blood vessels. (Hedge et al., 2005)
The history of nanofibers dates back to the late 1800s. Hughes and Chambers synthesized filamentous carbon in 1889. They used the gaseous blend of methane and hydrogen to grow carbon filaments via gas pyrolysis and carbon deposition (Wikipedia). Nanofiber manufacturing was first patented in 1902 by J.F. Cooley. He constructed a device called “Apparatus for Electrically Dispersing Fluids” (US Patent 692.631). (Lebrond, 2009) Nanofibers where previously called microfibers and were used in air filtration at the time. Nanofibers are usually fabricated through a technique called the electrospinning method. The electrospinning method uses nonwoven fabrics, which are textile materials random fibers connected by bonds of individual’s fibers without any stitching involved (Lee and Im). Electrospinning spins fibers ranging in diameter from 10 nm to several hundred nanometers. (Hedge et al., 2005) The first patent on electrospinning was created in 1934 by Formhals (US Patent, 1-975-504) (Frenot and Chronaki, 2003).
Russian scientists contributed a great deal to the nanofiber industry. Rozenblum and Petryanov-Sokolov, from the Karpov Institute in the former USSR, produced electrospun fibers in 1938. They were able to develop filter materials, known as “Petravanov Filters”, to capture aerosol that was used in nuclear power plants. In addition, the communist government placed electrospun cellulose acetate into factories during the 1940s. By the 1950s, the electron microscope was discovered and Soviet scientists were able to observe the structure of carbon nanofibers. In fact, the Soviet Scientist’s, Radushkevich and Lukyanovich published a journal article, in the Soviet Journal of Physical Chemistry, in the early 1950s illustrating the carbon nanofibers at a diameter of 50 nm. By the 1960s, Russia was electrospinning around 20 million m² per year. (Frenot and Chronaki, 2003)
The Western World did not have any type of written history during the Cold War. It wasn’t until the 1960s where work was released on a mathematical model regarding electrospinning. “The characteristic droplet shape of a fluid droplet in an electric field is still known as the Taylor cone (Vrieze and Clerck)”. The first manufacture of a nanofiber outside of Russia occurred in Japan during the 1970s. Later in the early 1980s, the manufacturing process began in the United States. Currently, the production of nanofibers is a multi-million dollar business with new engineering techniques for nanofibers to be used in many various applications (Sharing the Neurons).
Nanofiber layers are constructed using nylon spunbond (SB) material. The nanofibers are applied and impregnated to a specific ounce per square yard (osy) of nylon SB material creating a layer, which is laminated together. Different types of nanofiber composite fibers can be created using different thickness and weight of the SB material. The structure, performance and toughness of the nanofiber layers depend on the completed fabric design. (Hedge et al., 2005). There are two different types of designs. “The nanofiber/SB layer between outer shell layer fabric and chemical filtration layer” and “Nanofiber/SB layer is impregnated over the shell fabric and free floats against chemical filtration layer (Hedge et al., 2005).”
“The quality and characteristics of the final product are determined by the temperature, viscosity, elasticity, conductivity, and surface tension of the solution, strength of the electric field, distance between the needle tip and collector, and humidity (Heunis and Dicks, 2010; Huang et al., 2010; Liang, et al., 2007; Deitzel et al., 2001) Electrospinning with the solution of poly L-lactic acid (PLLA) at different concentrations in a chloroform solutions results in the production of nanofibers with different shapes or structures. For instance, electrospinning with 1% w/w (weight weight) of PLLA results in a “bead of a string” structure. Electrospinning with 3% w/w PLLA results in a smooth structure (Heunis and Dicks, 2010; Maretschek et al., 2008). Porous surface features are commonly used on nanofibers for deposition of nanoparticles on the fiber substrate. The modification of nanofiber surface morphology with pores increases the surface to area volume ratio,which allows for the use in applications such as chemical filtrations, tissue engineering, and fuel cell membranes. Porous nanofibers are obtained through thermally induced phase separation (TIPS) during electrospinning. (Esfandarani and Johari, 2010). Bi-component fiber structure is formed when two polymers are electrospun at the same time and side-by-side. The two polymers never come into contact with each other until the end of the electrospinning process, in which the fibers begin to form. This bi-component system allows for each of the polymer solution components to contribute something to the fiber, such as an increase in strength or wet ability. The bi-component fiber structure is most useful in the protective clothing industry. (Gupta and Wilkes, 2003)
Electrospun ﬁbers are sometimes too weak for use or handling, therefore, random nonwoven webs with aligned nanofibers are sometimes used and prepared with mechanical collectors and electric-field changes. In particular, yarn is developed in this manner. (Latifi et al.) “A dynamic liquid system in the form of a vortex is used to fabricate continuous twisted yarn. The nanoﬁber mat is narrowed and drafted off the water surface between the deposited area and the vortex. As the yarn is wound onto the bobbin, the yarn end on the water surface is rotated by the vortex, thereby twisting the yarn (Latifi et al.)” In addition, electrospun nonwoven webs composed of small micron diameters are used to grow soft tissues. The structures have a high surface area to volume ratio with an increased amount of pores. This allows for cell attachment and proliferation. (Gupta et al., 2007)
Natural fibers are the types of fibers derived directly from animals, vegetables or minerals. Natural fibers are finite in length and referred to as “staple” fibers. Natural fibers or staple fibers are used due to their structural fineness, impurity composition, color, water absorption abilities, thermal stability and resistance to chemical degradation. (Kroschwitz, 1990). Synthetic fibers are manufactured by man. There are numerous types of synthetic polymers that are used in the textile industry, such as polyamides, polyesters and polyolefins. (Kroschwitz, 1990)
Glass nanofibersare used, particularly in the medical field. Glass fibers are created to help with wound healing. The glass fibers are flexible and the structure of the fibers offers an increased surface area. In addition, the structure controls moisture levels and prevents the formation of bacteria or fungi on the wound. Furthermore, it is biocompatible.(Wray, 2011).
Inorganic nanofiberscan be formed from any type of metal, such as alkaline earth metals, metalloids, poor metals or transition metals when mixed with nitrogen, oxygen, phosphorus, sulfur or selenium. The inorganic nanofibers derived from metals results in a large surface area with strong mechanical properties. The fibers are useful in numerous textile applications. (CCTEC)
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