| In recent years,masks as the most effective protection methods have become necessities in human daily life due to COVID-19 and air pollution.However,a large number of discarded masks seriously endanger the marine and terrestrial ecological environment due to improper treatment and non degradablility factors.In addition,the masks on the market mainly rely on the electrostatic adsorption of melt blown electret nonwoven air filter material to remove the suspended micro particles in the air,which has the problems of unstable filtration performance and short effective usage time.Therefore,based on polylactic acid materials,this subject develops biodegradable high-efficiency and low resistance nanofiber mask filter element.（1）This subject took degradable polylactic acid（PLA）as raw material to prepare electrospun PLA nanofiber.Instead of low volatile dichloromethane,chloroform and other solvents in conventional electrospinning PLA process,dimethyl carbonate（DMC）was selected as a good solvent of PLA and forms a binary blend system with dimethylformamide（DMF）to improve the problems of volatile spinning solution,high conductivity and poor spinnability.The results show that when the concentration of PLA is 11 wt%and the ratio of solvent DMC/DMF is 7/3（v/v）,PLA nanofiber with average diameter of 187±16 nm are prepared which have uniform thickness and good morphology with no beaded structure.And the average pore diameter of the fiber membrane is2.56μm.The porosity is 88.9%,the filtration efficiency is 99.46%,and the resistance is only 81 Pa.（2）In order to further improve the filtration performance of PLA nanofiber membrane,the multi-scale structure was constructed and optimized by introducing ultra-fine PLA nanofiber,and the multi-scale PLA nanofiber filter material with high efficiency and low resistance was prepared.The results show that when the PLA concentration is 3 wt%,the high conductivity and ultra-dilute spinning solution was ejected from the Taylor cone in the form of fog and finally formed ultrafine fibers with an average diameter of 37±4 nm.The multi-scale structure of PLA fiber membrane was optimized by adjusting the number ratio of coarse and fine nanofiber spinning units.When the ratio was 3/3,the pore diameter of PLA fiber membrane was 0.73μm.The porosity is as high as 91.72%.Using the ultrasonic composite process,it was applied to the filter element of masks.When the gram weight of multi-scale PLA nanofiber membrane mask filter element was 0.91 g/m2,the filtration efficiency of PM0.3 is99.996%,and the pressure drop is only 104 Pa.In addition,when the membranec was placed in outdoor humid environment（humidity 90%）for 100 hours,the filtration efficiency is still>99.99%.In addition,it has good reusability and lasting PM2.5purification performance.（3）In order to solve the peculiar smell caused by bacteria breeding during wearing masks for a long time,multi-scale PLA nanofiber filter material with antibacterial properties was prepared through the combination of physical and chemical modification methods.The quaternary ammonium salt antibacterial agent dodecyl dimethyl benzyl ammonium chloride（DDBAC）was physically blended with spinning solution to prepare PLA scaffold nanofiber membrane,and then the membranes was aminated and chlorinated to introduce haloamine structure.The antibacterial modified PLA scaffold nanofiber membrane was used as the substrate to receive ultra-fine nanofibers,and finally a high-efficiency,low resistance and multi-scale PLA nanofiber filter material with antibacterial properties was prepared.The results showed that the active chlorine content of PLA scaffold nanofiber membrane was 68 ppm after amine hydrolysis and chlorination,and it had the renewable performance of active chlorine.When the content of DDBAC was 0.5 wt%,the multi-scale PLA nanofiber membrane could effectively resist bacteria,99.1%and 99.2%against E.coli and S.aureus respectively,while maintaining a high filtration efficiency of 99.991%and a resistance of only 107 Pa. |
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