"We are testing how our modification of nanofibre filters will withstand industrial use," says David Pavliňák
Our experts have devised a technique that facilitates the production of nanofibre mask filters. Now, with the help of a grant from the Technology Agency of the Czech Republic (TAČR), they are verifying how the plasma-treated surface of the filter handles temperature fluctuations, storage and other "pitfalls" of commercial production. For more, see the interview below with Dr. David Pavliňák, research and development worker at the CEPLANT Centre.
When the epidemic caused by the COVID-19 virus started, you became involved in the production of nanofilters in the voluntary group producing sewn cloth masks, as we wrote here?
Nanofibres are applied to the base material by electrospinning. This technology is based on the principle of spinning a polymer solution using a high electrical voltage. Primary fibres are first formed on the working electrode, which then "shoot" at high speed toward the counter electrode or collector due to the electric field. The voltage between the electrodes can reach up to 60,000 V.
The original primary fibre moves along a relatively complex trajectory in an electrical field, where the solvents evaporate and the fibre lengthens and thins, until finally the final product reaches the collector as a nanofibre. Compared to the original primary fibre, which is visible to the human eye, nanofibres range, on average, between tens to hundreds of nanometres. It is this property (i.e. a small fibre diameter, which causes the material to have a small pore diameter and, at the same time, a huge active surface) that makes the product so interesting for filtration applications. Nanofibres resemble non-woven fabrics (i.e. the white fabrics that you cover vegetables with in the spring to protect them from pests and frost), but they are much thinner so they can easily be torn or otherwise mechanically damaged. To combat this, nanofibres are often applied to a protective substrate, such as the non-woven fabric mentioned above, which then facilitates handling of the nanomaterial. Unfortunately, nanofibres do not adhere well to the substrate (they have poor adhesion) and tend to peel off. In addition, their upper side is unprotected and remains susceptible to mechanical damage.
DAVID PAVLIŇÁK graduated from Masaryk University’s Faculty of Science with a degree in Chemistry, with a focus on Materials Chemistry. Subsequently, he undertook a Doctoral study on Plasma Physics at the Institute of Physical Electronics. At present, he is working at the Centre for Research and Development of Plasma and Nanotechnological Surface modifications (CEPLANT), which is part of the ÚFE PřF MU. CEPLANT focuses mainly on applied research in plasma physics and materials engineering. David is 35 years old, married and has two children.
How was this problem solved during production in the spring?
We first applied the nanofibres to 50 cm wide and 800 m long rolls of non-woven fabric. We then handed over this material to colleagues at the Department of Chemistry, who then provided further processing (lamination, design, profile cutting, etc.). Final assembly of the masks and distribution was then undertaken along with volunteers from www.sijemerousky.cz. In this way, our chemistry colleagues managed to produce a functional nanofibre mask in a record short time,. From my point of view, I see lamination as a critical step. This is a procedure in which another protective layer is applied (glued or welded) to the nanofibres. This involves a further technological step in production which improves the material’s overall mechanical properties; however, it also reduces the breathability of the material. Thus, we decided to build on our previous research and omit the lamination step from the production process. We gained inspiration from plasma discharges generated at atmospheric pressure, which we have been studying for a long time as a means of modifying surfaces and improving adhesion properties of materials. In March, the COVID-19 ‘proof of concept’ was produced by TAČR. With the help of the Centre for Technology Transfer (CTT-MU), we then wrote a project proposal for this idea, which we finally obtained.
What exactly is plasma and how can it modify the surface of a material?
Plasma is generally known as the fourth state of matter, an ionized gas that is found in nature, e.g. in the form of lightning or in the solar corona. The particles in this type of plasma usually exhibit very high temperatures (up to millions of degrees Celsius). However, the plasma that we generate in our laboratories is different in that it is low-temperature (professionally, non-isothermal, with a low degree of ionization). Simply put, our type of plasma differs mainly in the different temperature of electrons (up to tens of thousands of ° C) and heavier particles (ions and gas molecules) which exist at ambient temperatures. Although the electrons have a high temperature (and therefore energy), they are not able to effectively "heat" the processed material due to their low weight. In the laboratory we are able to produce a high-energy and reactive plasma environment with a temperature of just 50 – 70 ° C. Consequently, we are also able to process temperature-sensitive materials such as polymer nanofibres. Plasma is an ionized gas, and thus its chemical effect will depend on the composition of the working gas. In our case, we generate plasma in the air; hence, we can expect reactive oxygen species, nitrogen oxides, ozone and various radicals, which mainly exibit oxidizing effects, in addition to energy electrons. Thus, the plasma does not heat the material, but contains particles that can "bombard" the surface of the material and thus change its physicochemical properties.
Could you describe the plasma processing of nanofibre mask filters in your laboratory?
When the base fabric is treated with plasma prior to electrospinning, its chemical-physical properties change to such an extent that the nanofibres "adhere better" to the substrate. Similar processing of the nanofibres themselves results in increased interconnection, which improves their mechanical resistance. We also change the pore size, surface structure and the chemical composition of the nanofibres. We believe that these effects could mutually increase filtration efficiency while maintaining the breathability of the material. We have achieved this using plasma sources developed at our workplace. In particular, recent innovations in the field of curved planar electrodes have led to the possibility of non-contact machining of materials sensitive to mechanical damage.
How did you innovate the Nanospider® production equipment?
The original electrospinning equipment, which was intended for laboratory testing only, was no longer in use. Some time ago, we reactivated it and had it equipped with a fully controlled external rewinder for the base fabric. It could be said that, in this way, we obtained a unit with a higher production capacity, to which we can then connect other technologies (e.g. plasma), and use it to demonstrate possible industrial applications. However, we were only verified the full potential of the device with the advent of the COVID-19 pandemic. At that time, using a four-member team, we were able to provide two-shift operation and produce kilometres of nanomaterial in just a few days.
In the spring of 2020, you applied for a grant from the Technology Agency of the Czech Republic as part of an extraordinary call for Proof of Concept (PoC) projects prepared by the MU Technology Transfer Centre. How did this go?
We received a grant from TAČR that allowed us to verify how the involvement of plasma technologies for the preparation of nanofibres would work, not only in the laboratory but also under industrial operation. The first laboratory experiments were successfully verified in 2017 and we published them in a professional journal (link here https://doi.org/10.1016/j.mtcomm.2018.07.010), though I must point out that, at the time, no one showed much interest. The idea that relatively "expensive" nanotechnologies would penetrate the production of disposable medical devices was pure economic sci-fi. A situation where people might sew masks at home on sewing machines had not occured to anyone. Then came COVID-19 and everything was different. We have since been approached by our standard industry partners, who now see that it makes economic sense to manufacture and sell such mask filters. By omitting the lamination step, we have an advantage over the competition. They no longer asked us whether it was possible to produce it, but what the involvement of the technology in in-line operation would look like and how the processed material would behave during long-term storage. Normally, it is not possible to raise funds for this type of research, thus it was a good thing that the special PoC challenge arose and that we were able to get involved in it. This research activity will be sponsored by CEPLANT (the Centre for Research and Development of Plasma and Nanotechnological Surface Treatments), which is a part of the Institute of Physical Electronics, Faculty of Science, Masaryk University.
What new questions does the possible use of technology in the commercial process bring? What exactly will you research?
Industrial operations, in contrast to laboratory operations, raises practical questions such as when we process the material using plasma, does it change the properties of the nanofibres? Does it become brittle? Will it last in stock, and for how long? We received the grant to test our ideas in practice and see whether the product would be suitable for industrial use. To do this, we are studying the effects of UV radiation and long-term storage. There are other companies with an interest in different results, so we have plenty of research tasks for the years ahead.
Does this method have potential for use with other products?
It started with masks but, in my opinion, it is necessary to focus on products and applications with higher added value, where the potential for the application of plasma technologies is higher. While we have concentrated on nanofibres and filtration to date, such as the production of a filter with an active antiviral barrier with a lifespan of 1 to 2 years, this same method could also find potential for use in car or aircraft air conditioners. But first and foremost, it's about verifying the technology.
How are students involved in this project?
Above all, we need experts in plasma physics and nanofibre technology. However, the topic is generally open to students, and we presently have one Doctoral and one Master's student working with us. In the future, we will certainly list topics for Bachelor's and Master's theses, and we would like to establish cooperation with the Department of Microbiology at the Faculty of Medicine, MU, and the Department of Experimental Biology in our own faculty. In cooperation with the Laboratory of Nanoparticle Synthesis of the Department of Chemistry at the Faculty of Science, , we also want to list a topics for Secondary School Professional Activity (SOČ), to which high school students interested in physics and chemistry can also apply.
And a final question: Do you promote CEPLANT activities in any other way?
High schools and other interested parties can come to us on excursions; we have prepared an interesting and rich program for them as part of events such as Scientists Night, the Open Day and other public events. We also work closely with the Department of Chemistry, organising international excursions for conservators and restorers from the Brno University of Technology and analysing their samples.
Thank you for the interview.
Authors: David Pavliňák, Zuzana Jayasundera
Translation: Kevin Roche
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