The principle of N95 mask blocking particulate matters

Whether it is medical surgical masks or N95 protective masks, their materials are essentially fibrous to filter particulate matter in the air. Therefore, it can be seen that factors such as the diameter of the mask fiber, the porosity of the fiber hole, and the thickness of the fiber filter layer will affect the effectiveness of the mask in blocking particles.

For the fiber layer to block particles, there are mainly the following mechanisms:

Settling effect: large particles settle on the filter fiber by gravity; Inertial impact: Due to the large inertia, large particles cannot follow the airflow to bypass the filter fiber, and then hit the filter fiber to be filtered;

Interception effect: When the medium and large particles pass through the filter fiber, they are intercepted by the fiber because of its too large radius;

Diffusion: Small particles are affected by the thermal motion of molecules and present the trajectory of Brownian motion, causing them to deviate from the direction of the airflow and “bump against” the fibers.

Electrostatic attraction: If the filtered fiber has a certain amount of static electricity, the particles in the airflow will be easily attracted by the static electricity and be filtered.

Of course, the above five mechanisms work comprehensively to protect particles of various sizes as a whole. Moreover, once the particles come into contact with the fibers and are blocked, they are difficult to detach due to the influence of the intermolecular forces and accumulate little by little on the face of the mask.

Therefore, as long as the air tightness is guaranteed, N95 is sufficient to block the filtration of particulate matter including pollen, PM2.5, and most bacteria. Of course, although the particle diameter of the new coronavirus is only 60-140nm (0.06-0.14μm), in fact the spread of the virus mainly depends on droplets and droplet nuclei as carriers (the diameter of droplets is generally greater than 5μm, while droplet nuclei are Less than or equal to 5µm, generally greater than 1µm), floating aimlessly in the air, so N95 is also sufficient for barrier.