Electrospinning industrialization

Electrospinning is not a new technology for polymer fibre production. It has been known since the 1930 s however, it did not gain significant industrial importance due to the low output of the process, inconsistent and low molecular orientation and poor mechanical properties of the electrospun fibres. 

This chapter is devoted to a discussion of the fabrication of nanofibres as a biomaterial and the use of them as such. Several approaches to this fabrication have been included, focusing on the extraction of nanofibrils from natural materials by both mechanical and chemical means and electrospinning from a wide range of materials (both natural and synthetic). Of these, electrospinning has received greater attention for a number of reasons it is convenient to operate, its processing parameters can be well controlled and it is the most likely to reach the scale of mass, industrial production. 

Widely used industrial approaches for the produetion of polymer fibres and yarns, such as coagulation spinning and electrospinning, have also been utilised for the fabrication of polymer nanotube eomposites. In coagulation spinning, for example, composite fibres ean be produced by an injection of surfactant-stabilised nanotube dispersion in water into a rotating bath of polymer e.g. PVA) dissolved in water sueh that nanotube and polymer dispersions flowed in the same direction at the point of injection. In this case, polymer molecules replace surfactant molecules on the nanotube surface, thus destabilising the nanotubes dispersion whieh eollapses to form a fibre. These fibres can then be retrieved from the bath, rinsed and dried. 

This chapter deals with nanofibers processed by electrospinning method, their applications in the composites industry, academic research and further developments in detail. 

In 1934 Formhals developed a feasible method [42] to obtain yarns via electrospinning. Somehow the technology was less appreciated and did not have either scientific or industrial importance. As nanotechnology became a well-researched field, several scientists began to focus on electrospinning in the 1990s. 

In our case, if the liquid jet breaks up and small droplets are formed, it is considered to be electrospraying, a spraying method generally used in the ink industry. If the jet can elongate without deflections, it is definitely electrospinning. 

There are several patents and methods describing modified electrospinning setups that make it possible to electrospin other materials or other formats for specific applications or to achieve better productivity. Some kind of rule of thumb is that modified spinneret electrodes should be used for higher output and modified collector systems developed have been to change the shape of the output material. A few of these inventions have begun to work on an industrial scale. 

Spinnerets are modified to get higher output, but the final product remains a fiber mat. In the electrospinning literature, capillaries made of metal or even glass are commonly used. One capillary can produce 0.01 to 2 g of nanofibers per hour, which is not an industrial... 

It is possible to produce composite nanofibers in an industrialized and cost-effective way as Kostakova et al. [121] did via needleless electrospinning from PVA (polyvinyl alcohol) with cross-linking agents where either MWCNTs or SWCNTs were applied as nanoreinforcement of the nanofibers. It is not obvious whether CNTs are embedded in the fibers in the case of needleless electrospinning because there is no continuous flow through a capillary that assures the CNTs flow with the liquid jets of electrospinning. Raman spectroscopy showed that CNTs are located within the fibers spun from the open liquid surface. 

Glass fibers are industrially produced from melt, above 700°C, that is why it is not used for melt-electrospinning. Bioactive glass fibers have already been produced via electrospinning from sol-gel [152] but they are not strongly related to PPCs. 

The optimal precursor material consists of fibers which are defect-free and continuous for industrial purposes. The solution and electrospinning process should be optimized considering the parameters affecting fiber quality, such as concentration, applied voltage, etc. [160,161]. 

Electrospinning has attracted great interest in the last few years since it is a cost-effective and feasible technology to produce nanofibers. Although these nanofibers have various applications, the propagation of them in the fields of composites is being established. There are several problems which have to be solved before industrialization. 

Analogous to HME, electrospinning is also a widely used technique in the polymer industry. A schematic of electrospinning process is shown in Fig. 3.11. A polymer solution is drawn through a capillary tube that is subjected to an electric field. As the electric field increases, the feed solution forms a Taylor cone at the tip of the capillary. Once the electric field overcomes the surface tension of the solution, the polymer solution is ejected as an electrically charged jet. Due to the increase in surface area, the solvent evaporates leaving thin filaments of material (50 nm to 5 microns). These fibers are then collected on collector screens for further processing. This technique has been applied for pharmaceutical systems by several researchers... 

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