Study On Correlation Between Crystal Phase Structure,Electret Properties And Filtration Properties Of Meltblown Polypropylene Nonwovens

With the intensification of air pollution in China in the past few years,smog weather is common in most cities across the country.On the other hand,with the improvement of living standards,people's requirements for air quality are constantly increasing,and there is an increasing demand for air filter devices such as air purifiers and personal protective masks,and thus air filter materials are getting more and more attention.Conventional air filtration materials only rely on mechanical barriers such as gravity deposition,inertial deposition,and Brownian diffusion to achieve the purpose of air filtration,so that when the material is to filter particles with relatively small particle size,it is necessary to improve the compactness of the material,which leads to the filter material.The permeability is reduced and the resistance is increased.In contrast,meltblown polypropylene electret nonwovens have a special electrostatic filtration mechanism,which has the unique properties of high efficiency,low resistance and antibacterial dust removal,and has become the main product in the current air filtration material market.However,in the actual use of the meltblown polypropylene electret nonwoven,the filtration efficiency will decrease with time,which will affect the service life of the material.The attenuation of filtration efficiency is mainly due to the weakening of the electrostatic field caused by the internal charge decay of the meltblown polypropylene electret nonwoven.Therefore,improving the charge storage performance and charge stability of the meltblown polypropylene electret nonwoven fabric,reducing the loss of charge in the body and prolonging the service life have become key issues that need to be solved.Existing studies have found that the crystal phase structure of meltblown polypropylene nonwovens is an important factor affecting the performance of its electrets.This paper attempts to improve the crystal phase structure of the nonwoven by doping different concentrations of stearate and heat treatment,using different charging methods to change the charge trapping properties of the nonwoven fabric,and adopting X-ray diffraction(X-ray diffraction,referred to as XRD)Analysis,Thermal Stimulated Discharge(TSD)technology and surface potential distribution measurement,such as crystal phase structure and electret research technology,combined with the test analysis of material filtration performance,studied the meltblown polypropylene electret non-Correlation of the crystal phase structure,electret properties and filtration properties of the woven fabric.The effect of phosphoric acid immersion on its electret performance,surface morphology and filtration performance was investigated by phosphorylation of melt-blown polypropylene nonwovens.The main results obtained are as follows:1.A meltblown polypropylene nonwoven fabric was prepared on a laboratory-made micro-meltblown experimental machine.The crystal phase structure of the nonwoven fabric is controlled by doping different stearate concentrations and high temperature aging.The crystal phase structure was analyzed and tested by XRD technique.The results show that the crystal form of the prepared melt-blown polypropylene nonwoven fabric is mainly pseudo-hexagonal crystal,after doping with stearate,the crystal form of melt-blown polypropylene is not changed,but stearic acid is doped.Salt can increase the crystallization rate of meltblown polypropylene,increase the proportion of a crystal form,the grain size,the crystallinity and the order of crystal,while the crystal form of the sample after aging treatment will be hexagonal crystal.The type is converted to the ? crystal phase,so that the crystallinity of the melt-blown polypropylene nonwoven fabric,the crystal grain size and the crystal order is increased.2.The charge storage characteristics of meltblown polypropylene electret nonwovens obtained by different injection methods under different concentrations of stearate were studied by thermal stimulation discharge technique.The results show that the melt-blown polypropylene nonwoven fabric usually has only one discharge peak on the TSD spectrum after constant temperature charging,but the high-temperature charging or doping with stearate can cause two discharge peaks on the TSD spectrum of the material.Explain that deep traps are also involved in the capture of charge.And when the added concentration reaches a certain size,a dipole peak appears on the TSD spectrum,indicating that a dipole charge has appeared in the material,because as the doping concentration increases,the stearate is no longer It acts as an auxiliary agent,but becomes a constituent,and the dipole peak on the TSD spectrum is provided by stearate.The charge stability and charge storage properties of meltblown polypropylene nonwovens can be improved by high temperature charging or doping with stearate,the charge stability and storage performance are superior with increasing doping concentration.3.The non-contact compensation method is used to measure the surface potential of the electret using a combination of a movable semi-automatic operating platform and an electrometer.The results of the analysis show that the surface charge distribution of the meltblown polypropylene electret nonwoven is not very good.Uniform,the positive and negative charge on the same surface is also inconsistent,doping with stearate or using high temperature charging treatment makes the surface charge distribution more uniform,and as the doping concentration increases,the surface potential uniformity is better,and The larger the area of the same polarity as the injection charge.The filtration performance of meltblown polypropylene electret nonwovens is limited by the uneven distribution of surface charge,so increasing the surface charge uniformity can improve its filtration performance.4.The filtration efficiency and resistance of the meltblown polypropylene electret nonwoven fabric obtained by different injection methods under the conditions of doping different stearate concentrations were measured by a filter efficiency tester,the gram weight and thickness were different.The materials were compared and analyzed.The results show that the resistance and filtration efficiency of meltblown polypropylene increase with the increase of doping concentration,which indicates that the melt-blown polypropylene nonwoven fabric can improve its filtration performance after doping with stearate.After the material is subjected to two different injection methods of normal temperature charging and high temperature charging,it is found that the filtering efficiency of the material after high temperature charging is greater than that of the normal temperature charging,but the resistance does not change.5.In order to explore the effect of phosphoric acid immersion on melt-blown polypropylene nonwoven fabric,the laboratory-made melt-blown polypropylene nonwoven fabric was subjected to phosphoric acid immersion treatment,and it was found that the original hydrophobic melt-blown polypropylene nonwoven after immersion in 24H phosphoric acid.The cloth becomes hydrophilic,but at this time it cannot form an electret by corona charging.After cleaning the phosphoric acid on the surface with deionized water,it was found that it could form an electret again,and the electret after forming the electret was the same as before the soaking.The surface morphology of the samples before and after phosphorolysis was observed by electron microscopy.It was found that the surface fibers became relatively rough due to swelling after phosphoric acid immersion,but the filtration efficiency was not improved.In summary,the filtration performance,electret performance and crystal phase structure of the meltblown polypropylene electret nonwoven fabric are closely related.The higher the crystallinity,the better the electret charge storage performance and the better the filtration performance.This study successfully achieved comprehensive control of the three properties,and the results obtained can provide theoretical and experimental guidance for the development and production of meltblown polypropylene electret nonwovens.