Research On Process And Charge Properties Of Polypropylene Electret Filter

Air filter material could prevent contaminants from entering the body, reduce particulate matter into the lungs of healthy and prevent the spread of disease. Polypropylene melt-blown nonwoven materials have been widely used in the medical field of health protection and air purification filters. For example, in the PM2.5 anti-dust masks, medical disposable masks, HEPA(High Efficiency Particulate Air Filter) materials and ULPA(Ultra Low Penetration Air Filter) materials, we all can see the PP melt-blown nonwoven materials. In theory, the finer the fiber, the more densely cohered fibers, the smaller the aperture, the filter material filtration efficiency will be higher.Filtration resistance and filtration efficiency is a contradiction. As the air filter material must balance the relationship between them. Electret process can solve this problem harmoniously. In theory, electret process means making non-woven fabric material obtained an electrostatic adsorption capacity by changing the external electric field. And then, the filter materials can be improved to have better filtration performance, especially filter the submicron particles.Until nowadays, there is no standard charging unit in manufacturing electret. Therefore, in this paper, a new corona charging system is designed according to the corona charging principle. This charging system had been designed twice. At last, the usability and the work efficiency are improved remarkably.Generally, the more electric charge the PP filtration material absorb, the greater its filtration performance would be enhanced. Thus, at first, a series trials are carried to figure out the relationships between charging parameters and the charging performance. Secondly, an orthogonal experiment is designed to find the best process parameters. Thirdly, many methods are used to discover how the corona charging influence PP material’s microstructure. At last, this study tests the change of surface potential changes over time.Several methods are used to test how corona-charge transform the original PP filter material, including scanning electron microscope tests, FTIR tests, X-ray photoelectron spectroscopy, air penetration tests, and so on. All of the results can lay the foundation to find out more ways to improve the effect of electret process. In the end of this paper, the BP artificial neural network model is established not only to find out a better understanding of the correlation between process parameters and obtained performance, but also to predict the will-obtained performance according to the settled parameters.Studies reveal that charging voltage plays the most important role on the surface potential. The higher voltage, the better charging performance. However, charging time and distance do less in improving charging performance. And when charged with signal needle pole, the charging area enlarge with higher charging distance. At last, the electret process could make the filter performance of polypropylene(PP) filter material enhance remarkably and do not change the air penetration performance. Also, high temperature treatment would enhance certain charging effects. The charged PP material’s surface potential would decrease quickly when deposited in unstable environment. However, when in mild environment, the surface potential will be stable. After one month, the surface potential decay is about 10%.