Study On Effect Of Electret Properity Of Meltblown Polypropylene Filter Materials

Meltblown nonwovens is widely used as sub high efficient and effective filter material with low resistance, common central air conditioning and home central air conditioning filter material and the electronics in industry for its high efficiency and has low resistance, small fiber linear density, surface area, and a series of excellent chemical resistance properties.But these products still have some deficiencies, such as filtration efficiency decreasing by time, poor charge storage performances.Particularly when they are used in high temperature or high humidity, the charge will decrease very quickly, even disappear. These factors largely influence the life of the product, but also increase the care and maintenance costs, making the use of such products limited.The physical properties of PP utilized in this study were as followingr:melt flow rate(MFR) of1800g/10min, melting point of165.18composition temperatures of260℃and final decomposition temperature of423℃.In melt-blown process, the effects of collection distance and air temperature on the web structure and properties were studied.The results showed that the collection distance almost had no significant influence on the fiber diameters, which were concentrated around1.7μm. The thickness of the product increases with increasing collection distance,the same as the maximum pore diameter and average pore size.As air temperature increased, the fiber diameter, maximum pore size and average pore size were shaping a decreasing trend.Treated with corona charging process, the effect of material properties and electret processes on filtering properties and electret properties of meltblown filter materials was studied.The results showed that:(1) In construction and propertiesthe,crystallinity degree had great impact on the stability of the space charge.The products with higher crystallinity degree had more stable space charge.When the process parameters were set,filtration efficiency and surface electrostatic potential of meltblown webs increased with decreasing fiber diameter.When the fiber diameter was controlled between0.5～3μm, the materials got preferable electret properties.The thickness had little effects on the filtration efficiency and surface electrostatic potential.As the thickness increased, the mechanical blocking mechanism enhanced, the corresponding filter resistance also increased. When the thickness remained at about0.5mm, the material got good mechanical filtration and electrostatic adsorption without increasing filtration resistance.Nonwoven webs with high porosity would obtain good dust collecting effect. While the web porosity was controlled around20μm,the products got the best pproperties.(2) Electretical conditions, such as charging voltage, charging time and charging distance,ambient humidity had an effect on electret properties of materials.The filtration efficiency and surface potential of the materials increased with the increasing charging voltage and charging time, while the filtration efficiency and surface potential of the materials decreased with the increasing charging distance and ambient humidity. Among the above factors, the charging voltage had the most significant effect on electrostatic potential of the sample, followed by ambient humidity. The charging time and charging affected least.Finally the study got the best process parameters: charging time of15min, charging distance of8cm, charging voltage of10kV, ambient humidity of35%.Finally, this paper proposed some method to improve electret durability of meltblown polypropylene filter materials,and put forward to the research directions for meltblown electret air filter materials.The combination with other technology was proposed to develop highly efficient air filter materials, which could clean indoor air pollution matter and remove harmful gas.