Preparation And Performance Research Of Water Electret And Corona Electret Meltblown Polypropylene Nonwovenfilter Materials For Air Filtration Applications

The problem of air pollution has always been the focus of all mankind’s attention.Particulate matter such as PM2.5 has a huge impact on human health,atmospheric environment and ecosystems.In order to ensure the safety of people’s life and work,personal protective masks,air purifiers and other air filtration devices have been widely used in various fields.Melt-blown polypropylene（PP）electret nonwovens are widely used in industrial and medical fields due to their excellent filtration performance.The COVID-19 outbreak has further highlighted the limitations of the previously widely used corona electret PP melt-blown filter materials.Therefore,relatively novel water electret technology has emerged in people’s eyes.Melt-blown PP water electret nonwoven air filter materials has quickly gained widespread attention due to its high efficiency,low resistance and excellent long-lasting stability of the electret effect.In general,the storage environment and application fields of electret filter materials have a great influence on the performance of the materials.The temperature and humidity of the environment have a greater impact on the filtration performance of the melt-blown PP electret materials.As the ambient temperature and humidity increase,the charge stored in the material will dissipate,which weakens the electrostatic adsorption effect of the material and reduces the filtration performance.The mechanism of corona electret is different from that of water electret,which results in the difference of the properties of the two kinds of nonwoven air filter materials.This article first explores the influence of the electret masterbatch and the electret method on the apparent morphology and microstructure of the melt-blown PP nonwoven air filter materials.Next,explore the difference between the temperature resistance and moisture resistance of the two electret materials;finally,explore the influence of aerosol flow rate and loading time on the filtration performance of the two electret materials,and analyze the transformation of the filtration mechanism during the loading process.The main research results are as follows:（1）The addition of electret masterbatch changes the structure of melt-blown PP macromolecular chain,increases crystallinity and increases grain order.Water electret treatment changes the fiber network structure of the material,corona electret treatment has no effect on the material structure.（2）The temperature resistance of the two electret materials is obviously different.The research data shows that: taking 90℃ treatment conditions as an example,the treatment time is 15 days,the filtration efficiency of the melt-blown PP water electret nonwoven filter material drops from the initial value of 99.89% to 89.46%,which is a decrease of about 10%.The filtration efficiency of the halo electret melt-blown PP nonwoven filter material is reduced from97.82% to 48.65%,which is about 49%.Therefore,the temperature resistance of the water electret nonwoven material is better than that of the corona electret nonwoven material.With the increase of the processing temperature,the crystal structure of the two electret materials did not change,but the order of the crystal grain arrangement increased.（3）The moisture resistance of melt-blown PP water electret nonwoven filter material is better than corona electret PP nonwoven filter material.When the relative humidity is 90% and the treatment time is 30 days,the filtration efficiency of the water electret sample decays from99.94% to 95.74%,which attenuates about 4%;the filtration efficiency of the corona electret sample drops from the initial value of 96.87% to 86.81%,a decrease of about 10%.Humidity treatment has no effect on the crystal structure of the material,but decreases the peak height of TSD curve discharge peak of the material.For this reason,this article speculates that the conductivity of the inner crystalline region and the amorphous region of the melt-blown PP nonwoven material is different,and interface traps are generated at the interface,and the interface traps will trap the charge generated in the electret process of the material.Most of the charge generated by the corona electret is stored in the material’s low-potential energy trap.When the temperature gradually increases and the charge gains energy to break free from the interface trap,the charge decays;when the humidity increases,the number of water molecules increased,the contact probability between water molecules and charge increased,the charge mobility increased,the attenuation rate is accelerated,and the attenuation range of filtration efficiency is large.Most of the charges generated by the water electret treatment are stored in deep traps with high potential energy.The deep trap charges have a large binding energy,and the environmental temperature and humidity have little influence on it.Therefore,the filtration efficiency of the material has a small attenuation range.（4）The time it takes for the filtration efficiency of melt-blown PP water-electret nonwovens to reach the lowest value is longer than that of corona electret nonwovens.The filtration efficiency of the water electret sample reached the lowest value after 18 minutes at a flow rate of 85L/min;the corona electret sample only took 11 minutes.As the aerosol flow rate gradually increases,the time for the filtration efficiency of the two electret materials to reach the lowest value decreases.As the loading experiment time continues to increase,in the initial stage,the filtration efficiency of the corona electret and water electret melt-blown PP nonwoven filter material first decreases,and then the filtration efficiency gradually increases after reaching the lowest value.The analysis believes that the filtering mechanism of the material has changed during the loading and filtering test.Before and after the loading test,the initial air permeability of the melt-blown PP water electret nonwoven material decreased from 225 mm/s to 194 mm/s,and the air permeability of the corona electret nonwoven material decreased from 155 mm/s to102 mm/s.The data results show that the air permeability of the melt-blown PP water electret nonwoven material is better.