| The main purpose of using masks is to prevent people from inhaling airborne dust,bacteria and viruses,etc.Both naturally occurring(volcanic eruptions,dust storms,naturally occurring fires)and man-made particles(such as industrial emissions)in the air are in the nanometer scale.Inhalation of nanoscale particles has serious respiratory and cardiovascular effects.Moreover,besides nanoparticles in the air,bioaerosols are also one of the health threatening factors.In 2020,the novel coronavirus spread around the world,and now the A virus is also threatening people’s lives and health.In this case,an effective solution is to use high-performance masks.Achieving a mask with optimal comfort,as well as high efficiency in eliminating bio-aerosols and optimal filtration of airborne particles has always been one of the goals of studies conducted in the field of air filtration materials.The base material of the mask is melt-blown polypropylene(MBPP)electret nonwoven,which has excellent filtration performance.The charging process enables MBPP nonwovens to be charged and become electret,so that it can more effectively capture airborne dust,bacteria and viruses,etc.At present,corona-charging and hydro-charging are the main technique.Although the MBPP electret nonwoven obtained by hydro-charging has higher filtration efficiency,hydro-charging has the disadvantages of complex process,longer time consuming and higher cost.Corona charging overcomes these shortcomings of hydro-charging and has become the most commonly used method of injection.However,the filtration efficiency of MBPP electret nonwoven fabrics after corona charging is difficult to reach more than 98%.The main reason for this problem is due to the lack of understanding of the charging mechanism of corona-charged MBPP electret nonwovens.In order to solve this problem,six charging modes are designed in this paper,and the influence of different charging modes on the charging performance,filtration,and sterilization performance of MBPP electret nonwoven fabrics is explored.In order to test the charge density of MBPP electret nonwovens better and more conveniently,a Faraday cup was designed and fabricated to measure the charge density.The main conclusions obtained are as follows:(1)In order to measure the charge density of MBPP electret nonwovens,the Faraday cup method is proposed,and the test device is designed and fabricated.Compared with the traditional thermally stimulated discharge(TSD)method and surface potential test method,the Faraday cup method has the advantages of simple operation,short measurement time and small error of test results.This provides technical support for better understanding of the charge density of MBPP electret nonwovens.(2)In order to prove the feasibility of the measurement device,the charge amount of samples with different areas was measured respectively.The test results of charge density and filtration efficiency,TSD current,surface potential were compared and analyzed.The results show that the relationship between the area of the sample and the amount of charge increases linearly,which is consistent with the theoretical formula of the device.Filtration efficiency,TSD current peak,surface potential,and charge density measured by Faraday cup all have positive correlations,which indicates the feasibility of the measurement device.(3)To address the problem that the correlation between charging modes and charge storage properties of corona-charged MBPP electret nonwoven is not clear enough,this paper uses six different corona charging modes to charge the material.The filtration efficiency measurement technique was used to evaluate the effect of different corona charging modes.The results show that the increase in filtration efficiency is closely related to the increase in current density and voltage magnitude during corona discharge.There will be a certain gap in the filtration efficiency of materials obtained in different charging modes,and the filtration efficiency of positive corona charging and positive-negative corona charging is the best.(4)The TSD current,surface potential and charge density of the samples obtained with six different corona charging modes were tested.The results show that the distribution of the surface potential is chaotic,the samples obtained by different charging methods are bipolar,and the surface potential has a certain relationship with the filtration efficiency.The experimental results of TSD illustrate the correlation between the filtration efficiency and the charge trapping performance of the sample.The trend of charge density is consistent with the filtration efficiency.(5)The antimicrobial properties of MBPP electret nonwovens obtained under different corona charging modes against bacteria and viruses were explored.The filtration efficiency of MBPP electret nonwovens with positive and negative corona charging.The inactivation performance against bacteria and viruses were tested.The experimental results show that the electrostatic field of the mask filter layer material can provide electrostatic filtration and inactivation of aerosol droplets containing Staphylococcus aureus,Escherichia coli and H1N1,regardless of how they are charged.The electrostatic field formed by the negative corona charging method is more conducive to enhancing the filtration and inactivation effect of bacteria.And the electrostatic field formed by the positive corona charging method is more conducive to enhancing the inactivation effect of viruses. |
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