Process:
As demonstrated in the figure the set up ofElectrospinning contains apparatus like a Sysringe, Pipette, metering pump,collector screen etc. An electrode is positioned into the spinningsolution/melt and the other is attached with a collector. The flow of polymersolution, contained in syringe is generated through by plunging the solutionthrough metering pump. A high voltage electrostatic force is generated betweenthe electrodes. When the fluid reached the open end of pipette it get stretcheddue to the force and start taking conical shape , which is generally referredto as "Taylor Cone". At a point of time the droplet overcomes surfacetension and move towards the collector screen in form of fluid jet. On its wayto collector screen the solvent evaporates and fibre of micro diameter areformed. These fibers are accumulated in collector screen.
According to Mr. Jon Stanger, Scientific Advisor to Electrospinz Limited, Electrospun fiber has three potential advantages depending on the application. First is by virtue of its small diameter the fibers have a very high surface area to volume ratio making them ideal for any application that depends on having a large surface area (e.g. catalysts, bioreactor substrates, active filtration). Second is by virtue of the mechanism of fiber formation where the fiber is stretched by a whipping motion while in flight giving a very high draw ratio. This potentially can result in a high degree of molecular alignment and minimize defects in the bulk material which would allow the fiber to attain a tensile strength closer to the theoretical strength (perfect for any high strength fiber application e.g. nanocomposites). Finally by virtue of the size and morphology that typical electrospun fiber forms (nano scale fiber diameter and pores between fibers in a mesh) makes it ideal for certain specialist applications (e.g. fiber size similar to collagen matrix in biological tissue so ideal for tissue scaffolds or nano pores in mesh are ideal for ultra-filtration).
Nick Tucker, Research Leader in biomaterials for Crop & Food Research while providing his experts comments on advantages and application of Electrospinning says "advantages of elecrospun material are intrinsic to the process. Electrospinning is a non-invasive method of fibre production. The process can run at ambient temperature and the process of solidification does not involve any coagulation chemistry, simply the removal of solvent from the system. This means that if we would like to produce a fibre with chemical functionalisation - say for example some kind of active filtration; for use in garment textiles this might the absorption of odour, or protection to the wearer from air-born pollution, we do not have to worry about the functionality being affected by the manufacturing process.
The range of materials available covers soluble artificial polymers such as polyvinyl alcohol, through to natural polymers - proteins and polysaccharides. It is also possible to process polymers from melted feedstocks if for example; residual solvent might be a problem in the product.
In terms of the fibre, the physical dimensions are important. The fibre diameter can be below the accepted level of nanoscaleawn fibre of this diameter should approach the maximum theoretical strength for the material used. For a typical nanoscale fibre it has been estimated that a single strand weighing less than 20kg would reach from the earth to the sun, but if that fibre was coiled up on the ground in a layer about 12microns thick, it would only cover the area of about twelve rugby pitches.
Note that the fibres are produced in a continuous length. This gives a notable advantage over other nano-scale fibres such as carbon nanotubes that are only available in micron lengths"
Commercialization of technology:
Despite having so many advantages, Electrospinning has still not find mass application in the industry. Many reasons are being cited by industry experts for this lack of interest by manufacturers in this technology. Firstly manufacturing nano fibres on industrial scale is a demanding process. Also as an emerging field nanofibre manufacturing process has many discoveries going on every day. This process change leads to changes in equipment requirements.
According to Mr. Jon Stanger electrospinning is quite easy to get started in (providing you are using a well behaved polymer/solvent system) it is extremely difficult to understand and master due to the large number of interdependent variables and the intrinsically interdisciplinary nature of the process. As such although a vast body of work has been published to date (~1,200 journal papers up to 2007 and ~1,460 patents up to 2006) it can be difficult for someone who is not an expert to enter the field and as such this provides a significant hurdle for any company wishing to use electrospun fiber. Additionally from the previously quoted figures there are currently more patents than journal papers making electrospinning a potential minefield of intellectual property. Finally there has been limited success so far at scale up of production of fiber creating another significant hurdle for any company wanting to use the fiber in a macro scale application rather than in nano scale quantities.
While Mr. Nick Tucker believes there is considerable growth in this field with companies like Elmarco making electrospinning plant at industrial scale as well as Electrospinz making the laboratory scale (eg www.electrospinz.co.nz). However, the materials produced are non-wovens, and the main application of these materials is in filtration (e.g. www.donaldson.com).
Although there are various developments in electrospinning field till date from 1902 when developments in this field started taking place and number of patents registered till date, not much actions is seen in mass production in the field. So it may be that the need to address technical difficulties in handling ultrafine fibres and the lack of an obvious economic benefit when electrospun fibres are considered as simple non-added-function replacements to readily available conventional fibres, has slowed mainstream production take up.
As we stand at the moment, electrospun fibres are usually presented for use on a conventional fibre substrate, so at the moment, the application in textiles would be in the area of added functionality rather than as direct production of entire textile materials.
Current market and future growth:
At present some companies like Donaldson are manufacturing their products using this technology. Donaldson use this technology for manufacturing Filtration products mainly. Recently, Donaldson introduced Ultra-Web nanofiber filter media for non-wovens and filtration industries for a broad range of filtration applications. Elmarco partnered with Liberec Technical University for NanospiderTM technology for the production of nanofibers. Elmarco has also produced pilot manufacturing line for production of nanofiber in 2004 and in 2006 offered the first models for industrial production.
Jon Stanger, Scientific Advisor to Electrospinz Limited when questioned about future of Electrospinning technology, said as with any high end specialty material electrospun nanofiber is unlikely to replace traditional fiber techniques. Rather it is more likely to become a valuable technique of producing fibers with either better performance or with functionality normally difficult or impossible to obtain using traditional methods bringing growth in new markets or in existing high performance materials and textile markets.
Mr. Nick Tucker commented, there is a very large quantity of academic research being done on the product of a wide range of electrospun materials. As ever, the limiting factor in commercial exploitation of this work is poor communication between the academic and commercial worlds. I believe there are great opportunities for commercial development waiting for exploitation. Commercial scale production plant for non wovens is already available, so at the moment all that is limiting growth in the market is that good ideas for novel fibres with interesting functionality are languishing on laboratory benches.
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