| Since the COVID-19,the demand and attention for masks have reached unprecedented heights.The core functional layer of the mask is a meltblown nonwoven material located in the core layer.In order to improve its filtration efficiency and maintain a low suction resistance,electrostatic electret method is often used to charge it.However,due to the late start of my country’s meltblown nonwovens industry and its slow development,there are fewer relevant research papers.At the beginning of the epidemic,various enterprises have transformed to produce meltblown nonwoven materials.However,due to the high barriers to meltblown technology and the serious lack of professionals,the quality of meltblown nonwoven materials is uneven.With the surplus of national anti-epidemic materials and the improvement of the domestic epidemic situation,in order to occupy a larger market,companies have begun to focus on water electret technology and introduce water electret production equipment,but there is currently no water electret technology at home and abroad,in addition to the detailed reports of the water electret masterbatch market,it has not realized the maximum potential of the water electret technology.Therefore,it is necessary to conduct a preliminary study on the mechanism of water electret to provide a theoretical basis for technological development and enterprise production.In order to achieve the goal of "high efficiency and low resistance" of meltblown nonwoven materials,this article first starts from electrostatic electret masterbatch.Different types of electrostatic electret masterbatches are added to the meltblown nonwoven material,to compare and analyze the filtration performance of meltblown nonwoven materials,the masterbatch is optimized.Further through elemental analysis、infrared spectroscopy and DSC tests on the electret masterbatch,it is believed that the preferred masterbatch is a compound electret and has good process compatibility with meltblown polypropylene resin.Further,meltblown nonwoven materials are prepared under different hot air speeds,DCD distances and electret voltages to optimize the production process.Through the analysis of the structural performance of the material,it is concluded that:(1)The hot air speed mainly affects the filter performance of the material by changing the diameter and unevenness of the fiber.With the increase of the hot air speed,the fiber diameter and unevenness are reduced,resulting in a decrease in the material pore size,and an increase in filtration efficiency and filtration resistance;(2)With the increase of the DCD distance,the fiber diameter and unevenness decrease,but at the same time,due to the decrease in thermal bonding and the pore size increases,the filter resistance and filtering effect of the meltblown nonwoven material becomes smaller;(3)The electrostatic potential on the surface of the electrostatic electret meltblown nonwoven material is randomly distributed,as the electret voltage increase,the electrostatic potential becomes larger,and the potential difference between the upper and lower sides also increases,and the filtration efficiency increases accordingly.However,due to the problem of charge saturation and voltage breakdown,the voltage should be adjusted according to actual conditions and cost requirements.According to the above results,the optimal process parameters of the experiment are determined as follows: the hot air speed is 900 rpm,the DCD distance is 200 mm,and the electret voltage is50 k V.Secondly,through the comparative analysis of the filter performance and tensile fracture performance of the inner and outer layers of the coil,the reason why the inner layer of the meltblown nonwoven coil is higher than the outer layer is explored,and the following solutions are proposed:(1)Reasonable control the diameter of the coil,adjust the winding tension in time to avoid obvious deformation of the inner material;(2)Add a cooling device to restore the material to room temperature before rolling,and reduce post-crystallization caused by insufficient heat dissipation inside the coil.In actual production,in order to ensure stable and uniform product quality,it is necessary to analyze the properties of the inner and outer materials of the coil.The results show that compared with the outer layer,the resistance of the inner layer is increased and the elongation is reduced.The reason for the increase in resistance may be that the winding diameter is too large or the winding tension is large during the initial winding,which leads to a certain deformation of the material and a decrease in porosity.For the above reasons,the winding diameter should be controlled reasonably,and the web speed and winding speed should be adjusted in time according to the tension.The reason why the elongation of the material decreases in the MD and CD directions is due to insufficient heat dissipation before winding and internal stress inside the material.The key to solving the problem is to add a cooling device to restore the material to room temperature before winding.In actual production,through the comparative analysis of the filter performance and tensile fracture performance of the inner and outer layer materials of the coil,it is found that the filtration resistance of the inner layer material is higher than that of the outer layer material,and the elongation in the MD and CD directions is lower than that of the outer layer material.In response to the above problems,we have proposed the following solutions:(1)Reasonably control the winding diameter,adjust the web speed and winding speed according to the winding tension in a timely manner,avoid obvious deformation of the inner layer material,and reduce the difference of the porosity of the inner and outer layer materials;(2)Add a cooling device to restore the material to room temperature before winding,and reduce the internal stress caused by insufficient heat dissipation in the material.Finally,simulated water electret device is used to conduct water electret treatment on the meltblown nonwoven material.Through the research of water quality,electret masterbatch composition and effect,fiber surface composition before and after electret,and electrostatic potential,preliminary research on the mechanism of water electret is carried out,and the following conclusions are drawn:(1)With the increase of water conductivity,the filtration efficiency of the material decreases;(2)Only the meltblown nonwoven material added with water electret masterbatch can achieve high filtration efficiency after electret;(3)Based on the experimental results of the elements on the surface of the fiber and the electrostatic potential after the electret,it is preliminarily inferred that the mechanism of water electret triboelectricity is electron transfer and ion transfer,but mainly electron transfer;(4)The TSD test was conducted on the water and electrostatic electret meltblown nonwoven materials,and it is believed that the charge amount and the charge stability of the water electret material are higher than that of the electrostatic electret material. |
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