We use cookies to improve our offer for you.You can find more information on this in our data protection declaration.Corona viruses are tiny - far too small to get caught in any sieve.So that they still don't get through the mask filter, engineers have to use various physical tricks.Where several people come together, they wear masks in Corona times.The medical mouth and nose protection and high-quality protective masks always have a special filter fleece installed.It is manufactured using the so-called meltblown process.The family company Reifenhäuser with its subsidiary Reicofil in Troisdorf near Bonn is one of the world market leaders for production machines that can produce such special nonwovens.Detlef Frey is Head of Research and Development at Reicofil.He opens the door to the technical center for us, where he and his colleagues are researching the production of so-called nonwoven textiles, i.e. fabrics made of synthetic fibers that do not have to be spun and woven first."We have 2,000 square meters and three production facilities here. Everything we have set up here corresponds to the systems that produce outside at the customer's," says Frey."We normally set up the systems here so that we can help customers develop products. Everything we do here with the recipes can already be used by our customers on site. However, due to the corona pandemic, we have decided to that we are now using the laboratory facilities to produce mask filter material."The starting material is the plastic polypropyleneAnd that should get all kinds of pollutants out of the air: In addition to viruses and bacteria, there are also grinding or other dusts, tiny aerosol droplets or asbestos fibers.In order for this to succeed, the fleece must be extremely finely structured.During production, the plastic polypropylene (PP) is first melted until it has the consistency of liquid honey.Then it flows through tiny nozzles and forms a wafer-thin thread underneath.But it's not as thin as it should be later.So it has to be made even thinner.To do this, the melted thread is blown.That's why it's also called "melt blowing", i.e. the meltblown process.Opinion on this: Mandatory face masks in Corona times?Nonsensical activism!Extremely thin, but extremely durable"Our polypropylene has a melting point of 160 degrees Celsius. The air is around 250 degrees hot. This hot air and the hot melt meet just below the nozzles and the liquid plastic is accelerated extremely strongly."The air catches the plastic threads at around 300 meters per second.That would be almost the speed of sound in a normal atmosphere.However, because the air flow hits the plastic threads from two sides and chaotic vortices also occur in a very small area, the relative speed acting on the endlessly long liquid plastic threads is multiplied.As soon as they are blown out of the nozzle, the cobweb-like polypropylene filaments fall down like snowFor a short time they are accelerated to almost 40,000 kilometers per hour - more than the orbital speed of the International Space Station (ISS).This makes the threads - also called filaments - incredibly thin.Although this speed cannot be measured, it can be calculated theoretically based on the actual filament strength later on."At the same time, we have to prevent the filaments from tearing off," says engineer Frey."It's fascinating to imagine that this plastic can withstand it and that we are able to manufacture a product of the same quality."More: Corona: The paradox of protective masksQuality control in the laboratory and on the machineIt's not easy, adds Alexander Klein, who works in the technical center as a development engineer."You have to make the settings in such a way that you have a homogeneous lay-up without imperfections, i.e. continuous filaments without filament breaks."Therefore, the control of the production process is important."We use inspection systems that optically find imperfections in the product," says Klein."On the other hand, we regularly take material samples that we test in the laboratory: air permeability and filter effect, so that we meet the specifications of the respective classification."In addition, sensors automatically measure, among other things, the air permeability of the finished filter material."Through testing, we can see when something is changing that indicates something in the process isn't working as it's supposed to," says Engineer Klein.More on this: Thinking in the intelligent factoryAlexander Klein controls the composite system, which simultaneously produces meltblown filters and spunbonded nonwovensAnd that can easily happen, because the threads are almost still liquid and quite sticky when they are swirled around by the hot air."These chaotic movements help us to form a tangle, i.e. a network. Because the plastic threads have not yet completely cooled down, they stick together. This network has a physical pore size of around ten micrometers - maybe a little smaller," explains research leader Frey .The filaments that make up the web are only half a micron thick.With a single seven gram thread, for example, one could encircle the entire earth.Such a thread would in turn be enough for about two to four face masks - depending on the mask quality.Viruses are much, much smallerAlthough it is already very fine, the nonwoven mesh would still not be sufficient to filter out viruses from the air based on their size alone.The openings in the filter material are around a hundred times the size of the virus, which is 0.12 microns.More on this: all-rounder nanoparticlesSo the engineers use physical tricks - such as the effort of small particles to attach themselves to surfaces."These are, for example, diffusion and inertia. On the way, the particle is deposited on the surface. It hits the filament and gets stuck on it due to frictional forces or intermolecular forces," explains Frey."Forces between molecules are important when we think in terms of viruses."But that still wouldn't be enough to filter viruses out of the air.The engineers also benefit from the fact that viruses usually have greasy surfaces."Polypropylene is lipophilic, meaning it attracts fat," he says.Viruses therefore get stuck on the fibers.But even then, a lot would still be left to chance.So Frey and his colleagues continue to help: "We have to introduce an additional force that separates and attracts the viruses. These are electrostatic forces, which we are currently using to a large extent."More on this: Elaborate all-rounders - nanoparticlesIt looks like this on the machine: During production, the finished fleece runs over a grounded roller.On the other side are numerous high-voltage electrodes."It's a relatively simple technology, but very effective," emphasizes engineer Frey."There are 30 kilovolts and a small current flows through the air that is ionized."The fleece then feels like an electrostatically charged mop, which you can buy in many drugstores for dusting.The filter material works the same way.The filter fleece runs over a grounded roller.Countless high-voltage electrodes are located above it"So I bring an electrostatic charge into the product, have a certain polarity and can then use it to exert forces - and now comes the limitation - on particles that are somehow conductive. As long as there is water, they are conductive."So that would apply, for example, to aerosol droplets that someone coughs up.As long as the viruses are already attached to these droplets or are swimming in them, the filter catches them - even if they are tiny.Isolated viruses that are completely free in the air could theoretically still pass through the filter if none of the other physically effective forces stop them.In practice, this is probably the exception rather than the rule.More: Coronavirus: How do high-security laboratories work?For a long time, researchers assumed that corona viruses can be infectious on surfaces such as door handles for an average of four to five days.However, recent research shows that they can even be infectious for up to 28 days - it mainly depends on the temperature.The viruses last the longest at 20 degrees Celsius.At 40 degrees only about a day.A certain amount of caution is therefore required when having lunch in the canteen - unless it has long since closed.In principle, coronaviruses can get onto cutlery or crockery if an infected person sneezes or coughs directly.However, the Federal Office for Risk Assessment (BfR) writes that "so far there are no known infections with SARS-CoV-2 via this transmission route".Do parents have to fear possible infection from imported toys?According to the BfR, there have so far been no cases in which an infection through imported toys or other goods has been detected.Initial laboratory tests show that the pathogens can remain infectious for up to 24 hours on cardboard and up to three days on plastic and stainless steel.In general, human coronaviruses are not particularly stable on dry surfaces.Because the stability of the virus outside of the human organism depends on many environmental factors such as temperature and humidity, the BfR considers infection via the postal service to be "rather unlikely".However, the institute admits that more precise data on SARS-CoV-2 is not yet available.Can my dog ​​infect me or can I infect my dog?Experts consider the risk of pets being infected with the corona virus to be very low.But they cannot rule it out.The animals themselves show no symptoms, so they don't get sick.However, if they are infected, it is possible that they transmit coronaviruses through the air they breathe or through excretions.The BfR classifies transmission of SARS-CoV-2 via contaminated food as unlikely.There have been no proven cases of infection so far.Thorough hand washing before preparing a meal should be a matter of course - even in times before and after Corona.Since the viruses are sensitive to heat, heating food can further reduce the risk of infection.Although the previously known SARS and MERS corona viruses do not like heat, they are quite insensitive to cold.They can remain infectious for up to two years in the frozen state at minus 20 degrees Celsius.However, the BfR gives the all-clear: So far there is no evidence of SARS-CoV-2 infection chains via the consumption of food, including frozen food.There is one good thing about the outbreak of COVID-19: China has banned the consumption of wild animals.There are many indications that the new corona virus was transmitted from bats to humans.The bat is not to blame, it had - probably against its will - contact with humans at a Chinese market.© 2022 Deutsche Welle |Privacy Policy |Accessibility Statement |Imprint |Contact |mobile version