How to store meltblown non-woven fabrics to ensure the best filtration efficiency

Melt-blown non-woven fabric is the core filter material of the mask, which is mainly determined by the filtering mechanism of the melt-blown filter material, which is mainly divided into mechanical barrier and electrostatic adsorption.

1. Mechanical barrier

Mechanical barrier has the following situations:

a. Foam can be blocked by filter material.

b. When the diameter of the fine dust is less than 3um, the fine dust is mechanically intercepted by the fiber layer of the curved pores in the filter material of the mask.

c. When the particle size and airflow velocity are large, the particles are captured due to inertial collision with the fibers, and when the particle size is small and the flow rate is low, the particles are captured due to Brownian motion hitting the fibers.

2. Electrostatic adsorption

Usually electret treatment is performed in the production process of meltblown cloth, so that the non-woven fabric has more static electricity and has electrostatic adsorption. Electrostatic adsorption refers to the capture of dust bacteria and viruses by the Coulomb force of the charged fibers when the fibers of the filter material are charged.

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 to form fine particles. Long hole channels prevent charge drift.

b. Charge traps are created by introducing additives with charge storage properties to capture charges.

3. Electret treatment

As can be seen from the figure, the key to improving the filtration efficiency of masks lies in the electrostatic storage of melt-blown non-woven fabrics. Under the mask circulation speed, the attenuation of static electricity is not a concern (for example, after leaving the factory, it will arrive at the user in half a month), and normal medical masks are valid for 6 months, while some masks in Japan are valid for three years.

The meltblown non-woven electret is very sensitive to ambient humidity. Sino's customer has done an experiment, stored for 7 days under normal temperature and high humidity (relative humidity greater than 95%), the surface potential of positive and negative corona-charged samples has decayed to 28% and 36% of the initial value respectively. At this time, because the melt-blown non-woven fabric has an open structure, its specific surface area is larger, and it has a larger contact surface with the surrounding environment, making it more sensitive to water vapor, corrosive gases, and charged particles of the opposite sex in the environment. The corona charging system can only generate ionic charges with low beam energy, and most of the charges injected during the charging process are deposited on the near-surface layer of the fabric surface fibers. When the sample is stored or worked in a high-humidity environment, a large amount of charge is lost due to the compensation effect of polar groups in water molecules and anisotropic ions in the atmosphere on the high concentration of surface charges on the fibers. Therefore, in the process of transportation and storage of meltblown cloth, it is necessary to avoid high humidity environment.

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