What are nanofibers?
Nanofibers are made from various natural polymers, such as cellulose, keratin, collagen, or synthetic polymers, for example PLA, polyurethane PU, PHBV, and many others. Each of these materials gives nanofibers their unique properties.
Scientists were able to produce the first nanofibers as early as in the first half of the 20th century and they are therefore not new to the scientific community, but in the past only a very limited number of nanofibers could be produced with the technologies available and therefore not suitable for widespread industrial applications. It was not until the turn of the 20th and 21st centuries that the technological sophistication of nanofiber production reached such an extent that nanofibers began to be produced in large quantities, thus opening up new opportunities for industry.
How are nanofibers made?
There are many ways in which nanofibers, both for experimental and industrial use, can be made. Among the most used methods of nanofiber production are used: melt-blown, electrospinning, drawing, centrifugal spinning, phase separation, hydrothermal method and more. Each of these methods has its specific advantages and disadvantages, whether it is the speed of production, the size of nanofibers and its deviation or the cost of production.
The production of nanofibers using electrospinning is very important for the Czech Republic, as the Czech scientific teams have managed to make great progress in the production of nanofibers using electrospinning. One of the best known is the "Nanospider" production line, which can use electrospinning to produce large quantities of nanofibers of adequate quality.
What is electrospinning?
Electrospinning is a popular method of nanofiber production, which uses several tens of kV in the production of high voltage.
In 1964, British scientist Geoffrey Ingram Talyor studied fluid solutions and their behaviour when exposed to high voltages. Taylor scooped up the solution into the needle and watched the drop on the tip of the needle behave under high tension. The drop with increasing tension changed shape until it reached the shape of a cone, and at the moment when the tension reached a critical limit, a fiber erupted from the tip of this cone. This phenomenon was named after its discoverer and is therefore known as the Taylor cone. In the case of solutions, the fiber continues to decompose into small particles in an electric field (a phenomenon called electrospraying); in the case of liquid polymers, the fiber does not decompose into small particles, but stretches.
This phenomenon is the basis of electrospinning. The polymer fiber, which is thus formed from the tip of the cone, begins to stretch in the electric field and thus at the same time taper until the fiber narrows enough to reach nanoscale. This fiber then hits the collecting plate, where it can continue to be worked with. An important skill in the production of nanofibers by the electrospinning method is the control of electrical voltage and its effect on the polymer solution, and this depends on many factors, including the parameters of the production machine.
What are nanofibers used for?
Membranes made of nanofibers can achieve smaller pore sizes, and thus filter even very small particles, and at the same time, nanofiber membranes can achieve higher porosity.
Nanofibers provide a suitable answer to this problem, because with the help of nanofibers it is possible to create suitable fabrics that have small enough pores that most bacteria do not pass through them and at the same time allow air to pass through well.
In tissue engineering, nanofibers play an important role in scuffold building for tissue cells.
How do nanofibers protect?
Thanks to their properties, nanofibers open up a new dimension of population protection. We know from experience with the COVID-19 epidemic that protective equipment, such as face masks and respirators, play a key role in protection and prevention. In this case, nanofibers bring improved properties of these protective devices and increase their effectiveness. At the same time, Czech companies have come up with various variations of these protective aids, such as washable nanofiber scarves or nanofiber mosquito nets that filter the air.
Nanofibers also help with air pollution. In many regions of the world, there is significant air pollution, which has a negative waste on the physical and mental state of the population. When air is polluted by smog particles, fine particles settle in the lungs, which limits their function. Particularly problematic are particles below the size of PM 10, ie particles below the size of 10 micrometers. These particles are dangerous because they are so small that they can travel deep into the lungs and the lungs have no defense mechanism to get rid of them, so there is no expectoration of the particles as is the case with larger ones. Depending on the filtration class of the material, nanofibers can help to filter these particles from the air and thus prevent the inhalation of harmful particles into the lungs. Nanofiber products that protect against smog include air handling filter membranes, face masks, scarves and nanofiber mosquito nets.
Nanofiber filtration membranes are already used in the field of water filtration, both in the field of microfiltration, ultrafiltration, nanofiltration, reverse osmosis or forward osmosis. Membranes made of nanofibers have better properties due to higher porosity and therefore require less pressure. Membranes are also used to desalinate seawater, which in some regions is the only way to obtain sufficient drinking water.
It is important to note that the fact that products contain nanofibers does not automatically mean that filtration occurs in the highest filtration class. It is the density of nanofibers and the size of the pores that determine the filtration quality of the product. Therefore, it is important to pay attention to the filter certification of the product. If the product has no certification, we recommend avoiding these products, as their filtration quality may be at such a low level that it has not passed the certification tests.
EN149 is a European standard that sets a minimum quality for respirators and masks that cover half of the face. This standard specifies the minimum tightness requirements for protective equipment as well as the parameters of the FFP categories. During the coronavirus pandemic, we could hear many times inflected FFP quality masks and respirators. FFP stands for "filtering facepiece" and is divided into three categories, the lowest filter category is 1 and the highest is category 3. In the US there is a different standardization and the equivalent of FFP is N. Below we can see a comparison of FFP and N standard, percentage is minimum capture requirement of all particles 0.3µm and larger.a
At least 80 %
At least 94 %
At least 95 %
N99 & FFP3
At least 99 %
At least 99,7 %