The influence of electret process conditions on electret performance
Corona charging is used to electret treat meltblown polypropylene nonwoven materials. The charging voltage, charging time, charging distance and ambient humidity play a significant role in the stability of the electrostatic charge carried by the air filter material.
The charging voltage has the most obvious effect on the electret effect of the sample, followed by the ambient humidity and charging distance, and the charging time has the least effect on the electret effect of the sample.
1, Charging voltage
As the charging voltage increases, the filtration efficiency of meltblown electret nonwoven material increases. This is because with the increase of charging voltage, the electret charge on the surface of the sample increases and the adsorption force on the particles increases, thus improving the filtration efficiency.
2, Charging time
With the increase of charging time, the filtration efficiency of meltblown electret material increases, and the influence law is similar to the influence of charging voltage. This is because the more the charging time, the more the charge captured on the sample surface, the more particles can be adsorbed, so the better the filtration efficiency.
3, Charging distance
The filtration efficiency of meltblown electret materials decreases as the charging distance increases. This is because the larger the charging distance, the less charge is captured on the sample surface and the less particles can be adsorbed, so the filtration efficiency will be reduced.
4, Environmental humidity
Theoretically, when the corona-charged meltblown nonwoven material is stored in the atmosphere, the ambient temperature has no significant effect on the charge storage life of its meltblown electret material. However, in general, both the filtration efficiency and the surface electrostatic potential of the material decay with time.
The influence of material structural properties on the electret performance
1, Crystallinity of polypropylene
Crystallinity is an important parameter of crystalline polymers and has an important impact on the physical and mechanical properties of the material. Factors affecting the crystallinity include the regularity of polypropylene, nucleating agents, etc., but the main role is played by the regularity. The higher the regularity and crystallinity of the material, the better the stability of the space charge and the stronger the crystallization ability.
2, Fiber fineness
Fiber fineness is one of the important parameters to determine the filtration efficiency and pressure loss of the filter material. The finer the fiber, the larger the surface area of the filter material, the larger the filtration coefficient, and the better the adsorption effect when the quantitative quantity of the filter material is the same.
The smaller the fiber diameter, the higher the initial filtration efficiency and the higher the initial surface electrostatic potential when other parameters of the fiber network remain unchanged. Since the surface charge strength of the material is proportional to the filtration efficiency, it is easy to capture more charged particles when the surface charge of the material is higher, which is beneficial to the filtration efficiency. However, when the fiber diameter is larger, the corresponding filtration resistance is smaller, which is favorable for the development of high-efficiency and low-resistance filtration materials.
In the actual storage process, the filtration efficiency of the material will change over time, with a downward trend, compared to the fiber diameter of large, small fiber diameter samples, its filtration efficiency is initially higher, with the extension of the storage time, the filtration efficiency of all samples decay over time, for the sample diameter is smaller, its filtration efficiency decline percentage is smaller, the filtration efficiency retention rate is higher, and thus the filtration efficiency is maintained more durable.
3, Pore size of the electret material
The pore size of the filter material is an important parameter in determining the filtration accuracy of the material, which determines the effectiveness of surface filtration. The filtering effect of porous filter material is achieved through its internal microporous channels, so the filtration accuracy of meltblown material depends largely on its microporous size.
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