Preparation,Performance Analysis,and Fluid Filtration Research Of Nanoscale Fiber Membranes

Due to their large fiber size,traditional filter materials such as melt-blown fiber,glass fiber,etc.,are difficult to further improve their filtration performance.In recent years,since the fiber diameter of electrospun membranes is one order of magnitude lower than traditional filter materials,more and more institutions have begun to pay attention to electrospun nanofiber membranes.However,so far,many fiber diameters in electrospun membranes are pseudo nanoscale and cannot truly reach the nanoscale（lower than 100nm）.Today,numerous reports have been on the refinement of electrospun fibers,such as jet stretching enhancement,multi-component spinning,core-shell spinning,and extremely dilute solution spinning.However,these methods are either complex or not technically mature enough to obtain many fiber materials with diameters less than 100nm.Based on the exploration of the formation mechanism of nanoscale fiber membranes,this thesis selected materials such as polyvinylidene fluoride（PVDF）,silicon dioxide（Si O₂）,polyvinyl pyrrolidone（PVP）,polyethylene vinyl alcohol（EVOH）,and polyethylene glycol（PEG）to prepare three different types of ultrafine nanoscale fiber membranes.By regulating the electrospinning process,hydrophilic modification of the fiber membrane,and self-assembly of solution molecules,the optimal spinning parameters and optimal spinning concentrations of PVDF,Si O₂,EVOH,and PEG were formulated.Based on the optimal spinning parameters and spinning concentration,further,adjust and control the preparation of high-efficiency air/water filter membranes,and conduct relevant testing and characterization of fiber morphology,electrospun nanoscale fiber diameter,fiber membrane pore size,hydrophilic and hydrophobic properties,breaking strength,chemical groups,and fiber crystals,providing a certain experimental basis and new research ideas for the preparation of high-efficiency air/water filter membranes.The main research contents and conclusions are as follows:（1）The factors affecting the fiber diameter during the spinning process were discussed through theoretical derivation,experimental verification,and literature support.On this basis,the feasibility of preparing ultrafine nanoscale fiber membranes by low-viscosity spinning was determined.In addition,to achieve high-efficiency air filtration,an organic-inorganic hybrid ultrafine nanoscale fiber membrane with high efficiency and low-pressure drop was prepared using low-viscosity electrospinning solution using electret PVDF and hydrophobic Si O₂ as raw materials.By testing the effects of PVDF concentration and hydrophobic Si O₂ concentration on the surface morphology and surface potential of ultrafine hybrid nanoscale fiber membranes,the optimal PVDF/hydrophobic Si O₂ concentration combination was selected.The research shows that when the concentration of PVDF is 4 wt%and the concentration of hydrophobic Si O₂is 0.7 wt%,the average fiber diameter of the hybrid nanoscale fiber membrane can be as low as 53.08 nm,and the average pore diameter can reach 0.43μm.The surface potential can be as high as 17.53 k V.The filtration efficiency of the hybrid nanoscale fiber membrane for PM_0.3 can be as high as 99.997%,and the air pressure drop is relatively low（only 114.46 Pa）.（2）Based on preparing ultra-fine nanoscale fiber membranes with low viscosity,it is further applied in water filtration.Further research was conducted on the pore size of electrospun nanoscale fiber membranes to improve filtration efficiency.Through experimental verification and literature review,it was found that reducing fiber diameter and changing fiber morphology can effectively reduce pore size.Through experimental verification and literature review,it can be found that reducing the fiber diameter and changing the fiber morphology can effectively reduce the pore size.Combining these two ideas,a minimum pore diameter PVDF/Si O₂/PVP hybrid nanoscale fiber membrane was prepared by the low viscosity spinning method,and its basic properties were tested.On this basis,the use of ethanol to remove PVP to prepare a curved nanoscale fiber membrane was carried out,and catechol（CA）,tannic acid（TA）,andγ-Hydrophilic modification of（2,3-epoxypropyl）propyltrimethoxysilane（KH560）.The results show that the hydrophilic nanoscale fiber membrane prepared has a small pore diameter（0.72μm）and a very low diameter（73.47 nm）.At the same time,due to the synergistic reaction of CA,TA,and KH560,a uniform hydrophilic layer can be formed on the surface of the fiber membrane.The hydrophilic nanoscale fiber membrane has an excellent hydrophilic effect（WCA=28.33°）,excellent oil-water lotion separation efficiency（>99%）,extremely high particle filtration efficiency（>99%）,and the LRV value of E.coli and S.aureus can reach more than 7.5.When the antibacterial concentration of the modified fiber membrane reached 6 mg/m L,the antibacterial rates against E.coli and S.aureus were 80.48%and 96.37%,respectively.（3）Due to the slow speed of self-weight filtration,it is difficult to meet the industrial demand for rapid filtration.During the filtration process,modified substances may fall off,resulting in a decrease in water flow.Therefore,a method of self-assembly of solution molecules was proposed,combining the principle of isotropic mutual exclusion of surfactant cetyltrimethylammonium bromide（CTAB）and tetrabutylammonium chloride（TBAC）,and using electrospinning to prepare self-assembled hydrophilic nanoscale fiber membranes with PEG as the outer layer.PEG and EVOH have good hydrophilicity,while hydrophobic PVDF is in the inner layer,so the fiber membrane has good hydrophilicity.By adjusting CTAB and TBAC in the spinning solution,further testing was conducted to observe the effect of CTAB and TBAC content on the fiber morphology of the fiber membrane.Research has shown that the self-assembled hydrophilic nanoscale fiber membrane has a smooth surface with nanoscale fibers（87.01 nm）and an average pore size of 0.61μm when CTAB=TBAC=1 wt%.The fiber membrane also has good hydrophilic properties,with a minimum water contact angle of 23.98°;Moreover,the filtration efficiency of 0.3μm polystyrene（air filtration）and 0.3μm titanium dioxide（particulate matter filtration in water）can reach over 99%,showing excellent filtration performance.In summary,three different electrospinned nanoscale fiber membranes have excellent filtration performance and nano scale fibers,each with its own advantages.After further research on filtration performance,they can be applied to the preparation of air/water filtration membranes.This study can not only provide a certain experimental basis for the preparation of electrospun air/water filtration membranes,but also provide new research ideas for the design of new filtration membranes.