Preparation Of PVDF-based Gradient Porous Structure Composite Nanofiber Membrane And Its Application In Air Filtration

The development of urbanization and industrialization has led to a series of air pollution problems,which greatly affect ecological safety and human health.In particular,airborne aerosol particulate matter（PM）,after being inhaled into the human fine bronchi and alveoli,carries toxic organic substances and heavy metal elements that can penetrate the alveoli and enter the bloodstream,causing serious harm to human health.Especially with the COVID-19 pandemic,the demand for protective masks has sharply increased,and air filters for personal protection have become a research hotpot.The core component of most current air filters is porous filtration material,which is usually made of micro and nano-scale disordered stacks of fiber membranes,such as melt-blown nonwovens,spun-bond nonwovens,vacuum extraction membranes,and electrostatic spun fiber membranes.Among them,electrostatic spun fiber membranes have been widely studied in recent years due to their micro and nano-scale diameters and small pore sizes,which can achieve a more efficient interception of PM.Since the diameter of the spinnable fiber or fiber membrane pore size is often larger than the PM particle size,air filtration materials often increase the filtration efficiency of the material through a strategy of increasing the membrane basis weight and thickness.However,the significant increase in material pressure drop greatly limits the application of such materials.In order to balance the filtration performance of fiber filter materials with pressure drop,structured design becomes a solution strategy.In this project,a monolayer multi-component fiber membrane with a pore size graded structure has been rapidly developed in one step,which uses a metal screen as the receiving substrate to achieve high efficiency filtration while maintaining a low pressure drop.Consequently,a multilayer composite antimicrobial fiber membrane with gradient infiltration has been constructed to achieve water directional transfer and inhibit the growth of germs with high efficiency and low resistance filtration.The main studies are as follows:（1）By using polyvinylidene fluoride（PVDF）,dibenzylidene sorbitol（DBS）and short-chain fluorinated alkyl modified silica（F@Si O₂）as spinning materials,an electrostatic spinning process is used to construct nanofiber membranes with pore size graded structure and charge regeneration.This fiber membrane pore size is directionally contracted along the direction of airflow movement,which can effectively balance the filtration efficiency and pressure drop.It captures PM with high efficiency(PM0.3>98.82%;PM0.5>99.87%,quality factor～0.121-0.507 Pa^-1;PM0.8-7.5=100%)while maintaining low pressure drop（55 Pa）and demonstrates excellent stability in acid,alkali,ultraviolet（UV）or high humidity environments.In addition,the piezoelectric properties of the nanofiber membrane itself enable the material to generate abundant renewable surface charge after pressing,achieving sustainable filtration of ultrafine particles（especially PM0.3）.（2）Polyvinylidene fluoride（PVDF）,Tetradecyl trimethyl ammonium chloride（TTAC）and organosilicon quaternary ammonium salt modified silica（S@Si O₂）are used as spinning materials,using an electrostatic spinning process,to construct antibacterial multilayer nanofiber membranes with graded pore size and diameter structure,which enable multilayer nanofiber membranes a functional that is directional water transport.The fibers are further refined based on the gradient porous network to enhance the material’s filtration performance for ultrafine particles(PM0.3>99.97%,quality factor～0.130 Pa^-1;PM0.5=100%;PM0.8-7.5=100%)while still maintaining a low pressure drop（71 Pa）.By laminating layers of hydrophilic PVDF-TTAC membrane,hydrophobic PVDF membrane and hydrophobically modified PVDF-S@Si O₂ membrane,the fiber membrane is endowed with gradient wettability for directional water transport.In addition,the composite fiber membrane has a significant antibacterial effect on E.coli and S.aureus,intercepting disease-causing aerosols while providing an efficient bactericidal function.