Development Of Transparent Modified Electret Nonwovens For Air Filtration

After being charged, the surface of polypropylene (PP) melt-blown materials is covered by electric charges which generate the Coulomb force made the filtration efficiency of the material increased dramatically without enhance the filtration resistance, thus PP melt-blown materials are widely used in the medical field of health protection and air purification filters as the PM2.5 anti-dust masks, HEPA (High Efficiency Particulate Air Filter) materials and ULPA (Ultra Low Penetration Air Filter) materials. However, due to the specific technical characteristics of melt-blown, crystallite dimension of the polypropylene melt-blown fiber is usually large and the degree of crystallinity is not high which affect the storage of the charge space. In order to improve the defects of electret material, we usually adopt the method of adding nano inorganic electret particles, such as SiO2, tourmaline. However, the physical and chemical properties of the nano particles will change greatly, and may freely across the cell membrane into the organism, and a large number of research papers and biological experiments show that the potential risks of nano-materials are indeed exist.So this paper takes a safer and more effective modified method that apply to high transparent PP plastic industrial production (such as baby bottles, cosmetic packaging) to decrease the spherulite size of polypropylene while increase the degree of crystallinity by adding clarifying nucleator to PP non-woven material thus to enhance the efficiency of electrets. At the same time, this method can improve transparency of non-woven materials more or less, so as to expand its application of air filtration, such as more beautiful high transparent anti-dust masks, transparent HEPA, anti haze screens etc.Firstly, two transparent nucleating agents (αnucleating agent) with different concentration were mixed with distinct kinds of melt-blown masterbatch, and then discuss the influence on transmittance, crystallinity and thermal properties of the modified material. Secondly, convert the modified material into non-woven and discussthe influence of melt-blown technology to the fabrics. Thirdly, according to the corona charging principle,a new corona charging system was invented, by using this system, series trials are carried to figure out the relationships between charging parameters and the charging performance, and then, find the best process parameters. At last, test the non woven fabricand complete the contrastive analysis. Research shows that:the melting temperature and crystallinity is increased while crystallite dimension is decreased by adding transparent nucleating agent. For example, adding NX-8000K to PP H39S-2, haze is reduced to 32.2% from 84.1%. Melt-blown process parameters and non-woven fiber diameter are closely related, in the meantime, the charging parameters play an important role on the surface potential, especially the charging voltage. At last, the electret process could make the filter performance of polypropylene (PP) filter material enhance remarkably, for instance, filtration efficiency is up to 81% from 30% and by adding transparent nucleating agent, it can further improve to 92% and the electret stability is also higher than before. At the same time, the appearance of this modified material is more transparent than ordinary PP.