The Structure Assemble Control And Perfprmance Of Nonwoven Material Based On Electrospinning For Air Filtration

A healthy atmosphere is the most basic condition for all living organisms to survive.However,the air quality is deteriorating due to the continuous production and diffusion of fine particulate matter(PMs),causing serious haze problems.According to statistics,about 544.9 million people worldwide suffered from chronic respiratory diseases in 2017,and the number of deaths caused by the diseases was as high as 4million.Pollutant particles suspended in the atmosphere are the main risk factors for chronic respiratory diseases.The main substance causing haze is fine particulate matter(aerodynamic equivalent diameter?10?m),which are a mixture of solid particles and aerosols.They are suspended in the air,causing great harm to human health and social production and life.At present,the main source of pollutant particles is the burning of fossil fuels.Humans cannot avoid using fossil energy in a short time.Therefore,the use of air filtering materials that can block pollutant particles to obtain clean air is one of the most feasible way to protect the respiratory system.Electrospun nonwoven materials have the advantages of small fiber diameter,small pore size,good pore connectivity,and large specific surface area,and have become an important research direction of air filtration materials.However,due to the densely packed two-dimensional structure of the material,it generally has a large filtering resistance when used in air filtration.In addition,there are also problems such as insufficient mechanical properties and excessive static decay.In order to overcome these problems,the current research focuses mainly on doping modification treatment,a variety of polymer blending and finishing processes,while there are few studies on improving the filtration performance through the control of the structure of the material.In this paper,three-dimensional fluffy structure,micro-patterned structure and electrospun nonwoven material that can convert pressure stimulation into electrical energy are prepared by three control methods:humidity control of the spinning environment,electric field control on the surface of the collector,and the use of composite piezoelectric effects.The preparation process and forming mechanism have been systematically studied and the application of these structures in air filtration has been discussed.The main research results obtained are as follows:(1)Aiming at the problem that the current electrospun air filter materials are mostly two-dimensional sheet-like structures and have small dust holding capacity,the main goal is to obtain electrospun nonwoven materials with a three-dimensional fluffy structure.Based on the Flory-Huggins theory,a three-phase system of"non-solvent-solvent-polymer"is constructed,and non-solvent substances are added to promote phase separation to control the structure of electrospun nonwoven materials.Polyacrylonitrile(PAN)is selected as the matrix polymer,and a water mist of 5.25 m L m^-3 is uniformly applied to the spinning collecting area to obtain the three-dimensional fluffy structure of the electrospun nonwoven material,and then the prepared material is placed in the desiccator containing N,N-Dimethylformamide(DMF)steam for cross-linking reaction.By controlling the cross-linking time,the material can be bonded at the cross position of the fiber to maintain the three-dimensional fluffy structure and improve the mechanical properties of materials.Scanning electron microscope(SEM)images show that the three-dimensional fluffy structure and the two-dimensional sheet-like structure of the fiber assembly are obviously different in structure and morphology.And when the three-dimensional structure of the electrospun nonwoven material undergoes steam cross-linking for 1 hour,the PAN fiber will only be point-bonded at the intersection point,which will not affect the overall structure and chemical composition of the fiber assembly.The breaking strength is increased by47.88%after cross-linking.The filtration performance test shows that the three-dimensional fluffy structure significantly improves the quality factor and dust holding capacity of electrospun materials.This structural control method has very important guiding significance for air filtration,oil-water separation and tissue engineering.(2)The space between the fibers in the three-dimensional fluffy structure is very large,leading to large average pore size and less universal.We focus on the patterned structure control of electrospun materials,namely by employing the novel collector with different aperture sizes to collect electrospun nanofibers.Design new collection device,that is,use metal rollers with honeycomb patterns with different side lengths as the collection device.Polysulfone(PSU)and polyurethane(PU)were spun simultaneously to prepare a PSU/PU composite electrospun nonwoven material with a regularly arranged honeycomb pattern structure.Affected by electric field,bumps,and hole size of collection device,the fibers are regularly deposited on the device,copying the hexagonal hollow pattern on the surface of the collection device.The forming mechanism of the micro-pattern structure was studied,and the hole structure on the surface of the collection device was designed and improved to realize the effective control of the average pore size of the electrospun material,thereby improving the filter resistance and the quality factor of the material.In addition,the honeycomb pattern structure has an impact on the mechanical properties of electrospun nonwoven materials.When the hexagonal holes in the micro-pattern have a suitable size(D?5 mm),it can bring positive effects to the mechanical properties of the electrospun material.Exploring the large-scale production of needle-free(spiral)electrospinning equipment has demonstrated the huge application potential in industrial and household filter materials.(3)Electrospun materials with the above two structures have the problems of static attenuation and inability to charge.Design and prepare electrospun materials with piezoelectric effect,which can convert external pressure stimulation into electrical energy of the material.However,pure electrospun materials are very easy to break under the stimulation of external pressure.Compared with the three-dimensional fluffy structure and the honeycomb structure(positive Poisson's ratio structure),the zero Poisson's ratio structure has better mechanical fatigue resistance.The electrospun material and the zero Poisson's ratio structural fabric(reinforced base material)are combined for structural control,combining the advantages of the two,and improving the fatigue resistance of the composite material.The experiment first studied the effect of spinning solution concentration on the morphology of polyvinylidene fluoride(PVDF)fiber and analyzed the content of?-crystal form in PVDF electrospun nonwoven material.The PVDF electrospun nonwovens with good filtration performance can be obtained by optimizing the PVDF solution with 18%(w/v)concentration and40 min spinning time,and the content of?crystal form in the material is as high as 84%.Then it is laminated with polyester(PET)warp knitted spacer fabric with zero Poisson's ratio structure to obtain PVDF electrospun material/PET warp-knitted spacer composite fabric.The results show that the PVDF electrospun material/PET warp-knitted spacer composite fabric not only has a piezoelectric effect,but also has a zero Poisson's ratio structure.The electrostatic adsorption performance of the composite fabric can be enhanced by compression impact,and after 9,000 compression impacts,the composite fabric can still maintain the original structure and mechanical properties,indicating that the composite fabric has excellent fatigue resistance.(4)After the preparation of PVDF/PET composite fabric,the problem that the electrospun air filter material cannot continuously generate charge to capture the polluted particles in the air,after preparing the PVDF electrospun material/PET warp-knitted spacer composite fabric,the goal is to use the piezoelectric effect of the material to continuously generate electric charge to capture pollutant particles in the air.Construct"wind wheel blade-crank slider"as the"pressure generating mechanism"of PVDF electrospun material/PET warp-knitted spacer composite fabric.A simple and practical filter device based on self-driving wind energy is designed and no external power supply is required.By collecting wind energy,the PVDF fiber deforms to generate electric charge under the action of the"pressure generating mechanism",which continuously"charges"the composite fabric for air filter.By exploring the actual size of each component in the device,analyzing and calculating the static characteristics of the wind turbine blades,the minimum starting wind speed of the device is calculated to be 2 m s^-1.Then use the finite element modeling analysis software COMSOL for simulation and calculation to judge the effectiveness of the device.Finally,under the conditions of high flow rate and high pollutant concentration,the actual filtering effect of the self-driving device is tested,which provides a new research idea for using the electrostatic adsorption to enhance the filtering performance of the material.