Electrospun fibres

Teo WE, Ramakrishna S (2005) Electrospun fibre bundle made of aligned nanofibres over two fixed points. Nanotechnology 16(9) 1878-1884... 

Shang SH et al (2010) The effect of electrospun fibre alignment on the behaviour of rat periodontal ligament cells. Eur Cells Mater 19 180-192... 

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. 

Table 4.1 List of polymer types/materials and properties/applications for electrospun fibres...

In a more recent work, MWNTs have been incorporated into surface-modified, reactive P(St-co-GMA) nanofibres by electrospinning. Then resulting nanofibres have been functionalised with epoxide groups and added to the epoxy matrix producing reinforced epoxy resins. The polymer composites have demonstrated over a 20% increase in flexural modulus, when compared with neat epoxy, despite a very low composite fibre weight fraction (at approximately 0.2% by a single-layer fibrous mat). The increase is attributed to the combined effect of the well-dispersed MWNTs and the surface chemistry of the electrospun fibres that enabled an effective cross-linking between the polymer matrix and the nanofibres. 

Although there are several SEEP formulations described in literature (Table 12.2), the most described and widely used is SELP-47K. Besides the ability to produce hydrogels, self-assembled structures and electrospun fibres, it is also possible to fabricate thin films by solvent evaporation at room temperature [65,66]. The major difference between hydrogels and thin films resides in the fabrication process and the resulting microstructure. Thin films of SELP-47K were made by dissolving the lyophilized powder in water and letting the solvent evaporate from the casting moulds [65-67]. Film thickness is controlled by the solution concentration and the volume used to cast. 

Doshi J, Reneker DH. Electrospinning process and applications of electrospun fibres. J Electrostatics 1995 35 151-60. 

Researchers have reported some properties of electrospun mats. They compared the performances of electrospun fibre mats with the properties of textiles and membranes currently used in protective clothing systems and showed that electrospun layers are extremely efficient for trapping airborne particles. Meanwhile, the air flow resistance and aerosol filtration properties are affected by the coating weight. It was shown that an extremely thin layer of electrospun nanofibres completely prevented particle penetration through the layer. 

It has been found that some morphological characteristics, such as fibre diameter and uniformity of the electrospun polymer fibres, are dependent on many processing parameters, which may be divided into three groups (a) solution properties (b) processing conditions and (c) ambient conditions. Each parameter affects the morphology of the electrospun fibres. 

A comparison between the diameter of the electrospun fibres and the electrical conductivity of the solutions is illustrated in Figure 4.6. A significant drop occurs in the diameter of the electrospun polymer fibres when increasing the electrical conductivity of the solution. 

Figure 4.13 Effect of tip-target distance on the electrospun fibre of fully hydrolysed PVAL. (a) 8 cm (b) 10 cm (c) 12 cm and (d) 15 cm...

We have also shown that electrospun fibres can be functionalised by the use of additives, and fillers of many kinds can be used to form composite fibres. The properties of electrospun fibres can be modified using nanosized fillers. Carbon nanotubes (CNT) are widely used as fillers in electrospun fibres. Typically, their function is to serve as a reinforcement component in electrospun polymeric fibres. 

F. Navarro-Pardo, G. Martinez-Barrera, A.L. Martinez-Hernandez, V.M. Castano, J.L. Rivera-Armenta, F. Medellin-Rodriguez, et al.. Effects on the thermo-mechanical and crystalhnity properties of nylon 6,6 electrospun fibres reinforced with one dimensional (ID) and two dimensional (2D) carbon, Materials, 6 (8), 3494-513, 2013. 

Finally, the mechanical properties of PLA-electrospun mats obtained by using different solvents were studied by Liao et al In particular, fibres obtained from a solution of PLA and chloroform (CHCI3) were prepared by using a collector disc with a centrifugal field of 1800 rpm. The experimental conditions used in this case, indicated with (a) in Table 6.4, are voltage 15 kV, flow-rate 0.25 mL h and distance between the needle and the cylinder 200 mm. Other samples, indicated with [h] in Table 6.4, were obtained from a PLA solution with a solvents mixture and a collector disc with centrifugal field 1800 rpm, flow-rate 0.25 mL h , 30 kV and distance between the needle and the cylinder 200 mm. From these results, it is worthwhile to note that the solvent and its evaporation rate strongly influence the PLA-electrospun fibres behaviour. The best results were obtained when a mix of tetrahydrofuran and chloroform was used. 

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