A sudden epidemic made anti-virus masks a hot topic. There are many types of masks on the market. Among these masks, medical surgical masks and N95 masks can play a good role in preventing viruses. So what is its anti-virus principle?
Medical surgical masks are generally divided into 3 layers: (inner layer) hygroscopic layer, (middle layer) core filter layer and (outer layer) water-blocking layer.
Compared with medical surgical masks, N95-level masks have been structurally optimized, and their core filter layers have more layers. Many, even manufacturers such as 3M and Honeywell use electrostatic treatment to enhance the filtration ability of fibers, so that the protective performance of masks is better.
Image source: Honeywell
The reason why these two masks are effective The key to anti-virus is that their core filter layer is composed of a layer of melt-blown non-woven fabric. The melt-blown non-woven fabric is a film made of polypropylene and made of many criss-crossing fibers laminated in random directions. , the fiber diameter range is 0.5~10μm, the scanning electron microscope picture is as follows.
It can be seen from the scanning electron microscope that the gaps between the fibers of the melt-blown nonwoven fabric are still very large, so how does it filter the environment? Viral? Although the size of the new coronavirus is very small, about 100nm, the virus cannot exist independently. Its main transmission routes are secretions and droplets when sneezing, and the size of droplets is about 5μm. Melt-blown nonwovens can filter droplets through a variety of filtration mechanisms. The fiber gaps can act as a ‘sieve’, but this is only one of the most basic interactions.
Depending on the size of the droplet particles and airflow velocity, fibers can capture virus-containing droplets through a variety of mechanisms:
• Inertia Collision – When large particles with large inertia encounter filter fibers, they cannot change direction due to their inertia, so they will hit the fibers and attach to the fibers.
• Interception – When particles move along the airflow and happen to come into contact with the fiber surface, medium-sized particles that tend to follow the airflow come into contact with the filter fibers and are intercepted by the fibers.
• Diffusion – When the particle size is extremely small, it is controlled by random particle motion (Brownian motion of small particles). The direction of movement deviates from the direction of the air flow and is adsorbed when it encounters fibers.
• Electrostatic attraction – When there is an electrostatic charge on the fiber, the electrostatic charge on the fiber will cause electrostatic adhesion to the particles.
For these interactions to occur, the diameter of the fiber must be as small as possible, and melt-blown nonwovens The fiber diameter in the cloth is between 0.5~10μm, with large specific surface area, tight arrangement and good filtration performance. Melt-blown cloth is used as the core filter layer in both medical surgical masks and N95 masks, so it has a good filtering effect on virus-containing droplets or aerogels.
Due to the melt used in N95 masks, Sprayed nonwovens have many layers, and excessive consumption of N95 masks will consume meltblown nonwovens resources too quickly, causing a more serious shortage of masks. According to the person in charge of the relevant production plant, the price of melt-blown nonwovens is currently rising and raw materials are in short supply. Therefore, we also call on readers to follow Academician Zhong Nanshan’s initiative and just use medical surgical masks in daily life, reduce the consumption of N95 masks, and leave production resources to medical staff and compatriots in epidemic areas who really need them.
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