Preparation Of Electret Melt-blown Nonwoven Composites And Study On Their Filtration And Antibacterial Properties

With the development of economy and society,the problem of air quality not only affects the ecological environment,but also causes great harm to human’s health.At the same time,the improvement of urban air quality brought about by the installation of air emission control systems and the development of various filtering materials is one of the most important achievements of China’s textile industry in the past two decades.Air filtration materials are widely used in production and life,such as various air conditioning filters,masks and so on.Especially since the COVID-19 pandemic began in late 2019,people have raised the requirement for air filtration materials used in masks.Melt-blown nonwovens are often used as the core filter layer of air filtration materials because of their good air permeability and excellent filter properties.The development of efficient and functional melt-blown nonwovens has gradually become a research focus.Like other air filtering materials,melt-blown nonwoven materials capture particles in the air flow mainly through interception effect,electrostatic attraction,inertial impact effect and so on,so as to achieve the purpose of air purification.Melt-blown nonwovens commonly used as raw materials for polypropylene（PP）melt-blown nonwovens,PP is a kind of polyolefin,is one of the three most widely used polymers,due to its suitable processing temperature,high tensile strength,good chemical corrosion resistance,low moisture absorption and other characteristics,is widely used in nonwovens industry.At present,research on improving the performance of melt-blown nonwovens mainly focuses on the following three aspects.Fiber fine densification and standing polarization are mainly to improve the filtering efficiency,while functionalization is to add antibacterial and antiviral effects.The finer the fiber,the higher the filtration efficiency.Industrial melt-blown fibers are usually 1-3μm in diameter,and increasing fiber fineness at the expense of production efficiency can lead to rapid cost increases.At the same time,because air filtration materials will capture and enrich bacteria in use,which may cause potential harm to users’health,the research and development of non-woven filtration materials with antibacterial effect is attracting more and more attention.At present,most antibacterial materials are attached to the surface of the material by the way of fabric finishing.In the process of use,antibacterial agents are easy to fall off,and the antibacterial effect is not lasting.Therefore,the development of"high efficiency,low resistance and lasting antibacterial"air filtration materials is of great significance.In this paper,the filtration performance of melt-blown nonwovens is improved by adding boehmite electret and standing polarization process.It was found that the fibers of melt-blown nonwovens became coarsen with the addition of boehmite electret,because boehmite would increase the viscosity of polymer system and affect the fluidity of polypropylene,cause the fiber to coarsen.Through thermal performance test,it was found that the addition of boehmite did not affect the melting of polypropylene,but reduced its decomposition temperature,which did not affect the melt-blown process,because boehmite would decompose and produce water at high temperature.Filtration performance test shows that the addition of boehmite electret has better filtration performance,and with the increase of boehmite content,the filtration efficiency first increases and then decreases.When the content of boehmite is 1.0%,the filtration efficiency reaches 96.3%,while the filtration efficiency without boehmite is 87.9%.In this paper,the electret process is optimized,and the electret polarization is carried out at different electret voltages,electret times and electret distances.The following conclusions are drawn through the surface charge test and attenuation test analysis:（1）The addition of boehmite effectively increases the surface charge of the electret non-woven fabric,and the surface charge increases with the increase of boehmite content.（2）The longer the electret time,the higher the voltage and the shorter the electret distance,the higher the surface charge of nonwoven materials,the longer the electret time and the higher the voltage will lead to the decrease of production efficiency,and the shorter the electret distance will lead to the ionization of air.The optimal electret conditions determined in this paper are:the electret time was 2 min,the electret voltage was 70 k V,and the electret distance was 35 cm.In order to ensure high filtration performance of melt-blown nonwoven materials with antibacterial function,different inorganic nano antibacterial agents were screened in this paper.First of all,the preparation of inorganic nano antibacterial particle doped electret PP masterbatch,and then through the melt-blown process to get the non-woven material,and then the electret treatment,and its morphology characterization and testing its thermal performance,filtration performance,antibacterial performance and so on.Nano zinc oxide（ZnO）can often be used as an economical inorganic antibacterial agent with photoactivity,The performance test results of ZnO doped boehmite electret nonwovens show that the antibacterial performance of nonwovens decreases with the increase of boehmite content.The main reason is that the antibacterial mechanism of zinc oxide is activated oxygen free radical produced by photocatalytic action,while the addition of boehmite can reduce its activity,resulting in the decline of the antibacterial performance of nonwoven materials.The results showed that ZnO antibacterial agent could not fully play the antibacterial effect while ensuring the electret filtration efficiency.And in most air filtration process,the filter material is not easy to see light.We selected nano silicon nitride（Si₃N₄）,a new nano ceramic material with antibacterial activity developed in recent years,which has been widely used in the field of biomedicine and has good biocompatibility and antibacterial properties.Nano-Si₃N₄was doped into boehmite electret masterbatch and processed into melt-blown fabric.The doping amount of Si₃N₄was 0.6%,0.8%and 1.0%respectively,and the content of boehmite was 1.0%.Through the test and analysis of its antibacterial performance,Si3N4 has obvious bacteriostatic effect,and with the increase of content,the bacteriostatic rate becomes higher,and the bacteriostatic rate of Escherichia coli and Staphylococcus aureus is more than 97%.The antibacterial mechanism of Si₃N₄is that in the atmosphere of H₂O,Si₃N₄will react with water to produce ammonia and free radicals with superoxidation effect,change the cell growth environment and destroy the cell structure,so as to achieve antibacterial effect.Si₃N₄doped boehmite electret melt-blown filter material is expected to be more widely used in the field of air filtration materials.