Production, Properties and End-Uses of
Nanofibres
O. Jirsák and T.A. Dao1
Abstract. Nanofibers are produces from organic and inorganic polymers via
electrospnning technology. Both polymer solutions and polymer melts can be
electrospun. Fiber diameters of 50 to 500 nanometers are typical. An industrial –
scale production method of nanofibres production has been developed. Small fibre
diameters and great specific surface are the main specific properties of nanofiber
assemblies, namely nanofiber layers. Number of specific end-uses of nanofibres
have been developed such as filters, sound absorbing materials, wound dressings,
scaffolds for tissue engineering etc. Machinery for nanofibres production is produced and offered in the Czech Republic. There is a great potential for utilization
of nanofibres in civil engineering.
1 Introduction
Although the idea of nanofibres production is rather old [1], technical interest in
,
this form of material started in 1970 s. Nevertheless, scientific and technical activities of a great extent appeared after the year 2000. Number of papers and patents on nanofibres is shown in Fig. 1.
1400
1200
1000
800
600
400
200
0
Articles
Patents
0
1
2
3
4
5
6
7
Fig. 1 Number of papers and patents on nanofibers in the years 2000 – 2007
O. Jirsák and T.A. Dao
Technical University of Liberec, Liberec, Czech Republic
e-mail: [email protected]
96
O. Jirsák and T.A. Dao
Beside papers and patents, some books on nanofibers appeared recently [1-4].
Nanofibers are one of three main types of nanomaterials, beside nanoparticles
and nanosurfaces. There are several laboratory methods of laboratory preparation
of nanofibres [2], nevertheless the electrospinning method is the most common
both in laboratory and industry. A laboratory electrospinning method based on a
syringe is shown in Fig. 2.
A)
B)
Fig. 2 A laboratory method of nanofibres preparation (A) and a detail of Taylor cone (B)
The device shown in Fig. 2 is used in many laboratories. It is not suitable for
industrial purposes for its low production rate, typically 0.1 to 2 gramms of polymer per hour.
An industrial method was developed [5] based on the roller as the spinning
electrode (Fig. 3).
Fig. 3 Roller electrospinning principle
In the roller spinner, the rotating roller (3) is immersed in a polymer solutionwhich creates a layer on the roller surface. Thousands of Taylor cones are present
on the surface of the roller due to high voltage and between the roller and the collector electrode (40). The nanofibres are collected on the textile backing layer
which is moving along collector electrode. Thus, a nanofibre layer is produced
Production, Properties and End-Uses of Nanofibres
97
continuously and the production rate is high, depending on width of the machine,
number of spinning rollers and required area weight of nanofibre layer.
2 Properties of Nanofibres and Nanofibre Layers
Typical properties of nanofibres with comparison with conventional textile fibres
and special, extremely fine “melt blown” fibres are shown in Table 1.
Table 1 Typical dimensions of conventional fibres, melt-blown fibres and nanofibres
Fibre diameter
( μ m)
Linear density
Specific surface
(dtex)
(m /g)
10-40
1-30
ca. 0.2
Melt-blown
1-5
ca. 0.01
ca. 2
Nanofibres
0.05–0.5
ca 0.0001
ca. 20
Fibres
Conventional
2
Nanofibres are produced from a variety of organic and inorganic polymers such
as polyvinylalcohol, polyamides, polyurethanes, polyimides, polystyrene, pHEMA, chitosan, co-polymers, polymers containing a variety of additives, silica
and many others.
Nanofibre formations of various forms can be produced depending on the shape
of collector electrode such as planar layers, yarns, nanofibre coated yarns, tubular
bodies, 3D scaffolds for tissue engineering and others. Some of them are shown
in Fig. 4.
Great specific surface area together with small fibre diameters allow rapid interactions of materials with surrounding media. As an example, release of water
A
B
Fig. 4 Planar nanofibre layer (A) and a yarn coated by nanofibres (B)
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O. Jirsák and T.A. Dao
Fig. 5 Release of a dyestuff from
nanofibres into water
100
90
Efficiency (%)
80
70
meltblown
60
charged meltblown
50
glass microfibers
40
needle punch
30
PA6 nanospider
20
PA6/PU nanospider
10
0
50
100
150
200
250
300
350
400
450
500
Pressure drop (Pa)
Fig. 6 Filtration efficiency versus pressure drop of various filter materials
soluble dyestuff from nanofibres and from thin foils is compared in Fig. 5. Release
from nanofibres is rapid and almost complete whereas that from foil is slow and
incomplete. Fig. 5 illustrates differences in interactions with surrounding media
between nanomaterials and macroscopic bodies. Variety of specific end-uses of
nanomaterials is based on their specific properties such as filters, semipermeable
membranes, scaffolds in tissue engineering, wound dressings, chemical and biological protective clothing, energy storing, sensors, composite reinforcements and
many others.
3 Examples of Nanofibre End-Uses
Excellent filtration properties of extremely thin (0.05 – 0.1 grammes per square
meter) nanofibre layers are shown in Fig. 6 in comparison with other typical filter
materials. Nanofibre layers show a very high filtration efficiency whereas maintain low values of pressure drop.
Voluminous materials composed of nanofibres and textile fibres layers (Fig. 7)
show specific sound absorbing properties. In comparison with conventional sound
Production, Properties and End-Uses of Nanofibres
99
absorbing materials such as fibrous layers or polyurethane foams, the composites
containing nanofibre layers absorb sound effectively at lower frequencies (Fig. 8).
The effect consists in the ability of extremely light nanofibre layers to echo with
sound waves and to transfer the energy into the layer of textile fibres.
It is possible to grow human and animal cells as well as bacteria on the nanofibre layers. Therefore, the materials are used in tissue engineering and decontamination technologies (Fig. 9).
Fig. 7 Layer of nanofibres and textile fibres
Fig. 8 Sound absorption coefficientsvs.
sound frequency (lower line-no nanofibres)
Fig. 9 A nanofibre layer covered with bacteria
References
1. Reneker, D.H., Fong, H.: Polymeric Nanofibers. American Chemical Society, Washingon (2006)
2. Ramakrishna, S., Fujihara, K., Teo, W.E., Lim, T.C., Ma, Z.: Electrospinning and Nanofibers. World Scientific Printers, Singapore (2005)
3. Brown, P.J., Stevens, K.: Nanofibers and Nanotechnology in Textiles. Woodhead Publishing Limited, Cambridge (2007)
4. Andready, A.L.: Science and Technology of Polymer Nanofibres. John Wiley and Sons,
Inc., Hoboken (2008)
5. Jirsak, O., Sanetrnik, F., Chaloupek, J., Martinova, L., Lukas, D., Kotek, V. (2005) Patent
WO2005024101