1. Mechanical barrier
Mechanical barrier has the following situations:
a. Droplets with a particle size greater than 5um in the air can be blocked by the filter material.
b. When the diameter of the dust is less than 3um, the dust will be mechanically intercepted by the curved pore fiber layer in the filter material of the mask.
c. When the particle size and air velocity are both large, the particles will be captured due to inertia collision with the fiber. When the particle is small and
the flow velocity is low, the particles will be captured by impacting on the fiber due to Brownian motion.
Usually during the production process of melt-blown cloth, electret treatment is used to make the non woven cloth carry more static electricity and have electrostatic adsorption effect. Electrostatic adsorption means that when the fibers of the filter material are charged, the Coulomb force of the charged fibers realizes the capture of dust bacteria and viruses.
There are two ways to improve the charge storage capacity of electret materials:
a. By improving the crystallinity and mechanical deformation of the material, the structure of the material is changed, forming a slender hole channel to prevent charge drift.
b. Generate charge traps to capture charges by introducing additives with charge storage properties.
3. Electret treatment
The key to improving the filtration efficiency of masks lies in the electrostatic storage of meltblown non woven fabrics. At the current rate of circulation of masks, the attenuation of static electricity is insufficient. Normal medical masks are valid for 6 months, while some masks in Japan are valid for 3 months. year.
The meltblown non woven electret is very sensitive to environmental humidity. When stored for 7 days under normal temperature and high humidity (relative humidity greater than 95%), the surface potential of the positive and negative corona charged samples has decayed to 28% and 36% of the initial value, respectively. At this time, because the meltblown non-woven fabric has an open structure, its specific surface area is larger, and its contact surface with the surrounding environment is larger, making it more sensitive to water vapor, corrosive gases, and heterogeneous charged particles in the environment. At the same time, The corona charging system can only generate ion charges with low beam energy, and most of the charges injected during the charging process are deposited on the near-surface layer of the cloth surface fiber. When the sample is stored or working in a high-humidity environment, a large amount of charge loss will be caused due to the compensation effect of the polar groups in the water molecules and the foreign ions in the atmosphere on the high-concentration surface charge on the fiber. Therefore, in the process of transportation and storage of meltblown cloth, high humidity must be avoided.
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