In the face of the new coronavirus epidemic in early 2020, people across the country are united in their hearts and minds to overcome the difficulties. During the epidemic, masks, thermal guns and other materials became the "small partners" of daily contact ". Friends often ask Xiao Bian: how to tell if the mask I bought is real or fake?

It is actually very difficult to answer this question accurately. The national standards "GB/T 32610-2016" and "GB 2626-2006" all have strict regulations on respirators and other respiratory protective articles, and have clear experimental test methods and judgment standards from the filtration efficiency, leakage efficiency, expiratory resistance, air tightness, dead cavity and other indicators. Although this kind of standard is accurate, it is also cumbersome. Although it can determine whether the mask is true or false, it is difficult to determine whether the mask is "second-hand" (because many second-hand masks are processed and the main indicators are the same as new masks).

Do we have an experimental method that can achieve rapid screening with high accuracy and identify whether the mask is "second-hand?

It is well known that the protection of masks against dust and spittle (the protection of viruses is also through the protection of virus-carrying spittle) mainly depends on its physical properties, and the fiber thickness, pore size and thickness of the filter layer of the mask will directly affect the protective ability and filtration efficiency of the mask. If we can directly observe and test these indicators, will we be able to screen masks quickly and effectively?

In addition, the editor also did mask testing in high air pollution environments and mask testing in second-hand smoke environments to verify the need for respiratory protection in these environments.

In order to verify the above conjecture, Xiaobian used a desktop scanning electron microscope and collected various masks to do a series of comparative experiments.

Figure 1(1) A common medical surgical mask 1;(2) A common medical surgical mask 2;(3) A medical surgical mask that has been used for 4 hours in total;(4) The "three-no" mask to be identified;

Figure 2 Scanning electron micrograph of the middle filter layer (meltblown cloth layer) of the medical surgical mask 1. It can be seen that the layer is densely arranged with 1-15 um fiber structure.

Figure 3 Scanning electron micrograph of the middle filter layer (meltblown cloth layer) of the medical surgical mask 2. It can be seen that the layer is densely arranged with 1-15 um fiber structure.

FIG. 4 The middle filter layer (meltblown cloth layer) of the medical surgical mask 3 that has been used for 4 hours. The fiber structure arrangement is similar to the first two, and particles with a diameter of 3-4 um are found.

Figure 5 Scanning electron microscope image of the middle layer of the "three-no" mask to be identified. The fibers are very coarse, generally above about 15 um, with coarse holes. Such large pores do not effectively filter contaminants.

Figure 6 Scanning electron microscope image of the cross-section of the middle filter layer (meltblown cloth) of the medical mask. From the cross-section, the fiber arrangement is dense, and there is an obvious impression mark in the middle, which is caused by the suppression of the mask production process.

Figure 7 Cross-sectional scanning electron microscopy of the middle layer of the three masks. It can be seen that the fibers are loosely arranged, the fibers are thick, and the holes are large, which cannot be effectively filtered.

We just saw the scanning electron microscope image of a medical mask worn for 4 hours in a daily environment. There are very few particles on it, which also shows that the space of our daily life is actually relatively clean. What if we change to a highly polluted environment? We want to simulate a highly polluted environment and a mask in a second-hand smoke environment for comparative experiments.

Figure 8 The scanning electron microscope image of the middle filter layer of the mask worn under the simulated high pollution environment.

In order to avoid pollution causing harm to the human body, we put the mask on the car vacuum cleaner and pumped for 5 minutes in a highly polluted environment. At this time, the inhalation volume is similar to that of human breathing for 4 hours as a reference. We can see that the mask filter layer is densely covered with 2 - 15 um size particles. If there is no mask filter, these particles will all be sucked into the lungs and cause harm to the human body.

What about the second-hand smoke environment?

Figure 9 Scanning electron microscope image of the middle filter layer of the mask worn in the second-hand smoke environment.

Similarly, we use a vacuum cleaner to replace the human mouth and nose. In a closed room full of smoke for 5 minutes when the inhalation volume is similar to that of human breathing for 4 hours, as a reference. Similar to the highly polluted environment, the filter layer of the mask is also covered with large and small particles. If you do not wear a mask, these particles will be directly inhaled into the lungs. So, for the health of the family and the people around you, it is better to smoke less.

Conclusion:(1) The fiber of the filter layer of the good medical mask is about 1-15um, and it is very dense, which can effectively isolate pollution and virus-carrying saliva;

(2) The fiber of the filter layer of the inferior mask is thick and fluffy, and there is no way to filter most pollutants;

(3) The quality of masks can be quickly distinguished within a few minutes by using scanning electron microscope for this test sample, but there is a lack of a large number of samples to support it. It is hoped that people of insight can participate in the design and sampling together to further speed up and optimize the detection efficiency of masks.

(4) A large number of polluting particles will be produced in highly polluted environment and smoking environment, so medical masks must be worn, please also reduce smoking for the health of your family and friends around you.

References:

1. National Standard GB2626-2006 Respiratory Protective Equipment

2. National Standard GBT_32610-2016_Technical Specification for Daily Protective Masks

3. Baidu Encyclopedia (Masks):

https://baike.baidu.com/item/口罩/3416459?fr=aladdin

This experiment was completed by using the first fully independently developed desktop scanning electron microscope ZEM15 in China:

For more experimental details and research cases, please send an email to support@zeptools.com for details. Welcome to the company's website: http://www.zeptools.com

ZEM desktop scanning electron microscope