Construction Of Pvdf Nanofiber Membrane With Multi-scale Structure And Its Application In Air Filtration

Electrospinning technology has made rapid development in the field of air filter materials because of its structural characteristics with submicron fibers(100-1000 nm)and small controllable pore size.However,there are still some problems worthy of attention in the conventional nanofiber materials prepared by electrospinning,mainly including:(1)the diameter of nanofiber is difficult to be further refined,which is limited by the submicron PM_0.3(particle size 300 nm)particles still have the problem of low filtration efficiency.(2)Single scale nanofibers still have the problem of close packing,and it is difficult to balance the filtration efficiency,filtration piezoresistance and light transmittance.(3)Although conventional electrospun nanofibers are easy to be modified,they usually sacrifice the filtration performance in the application of air filtration materials in order to achieve multi-functional effect,which greatly limits their practical application.To solve the above problems,superfine polyvinylidene fluoride(PVDF)nanofibers with a diameter of 15-25 nm were prepared by electrospinning technology using a solution system with high molecular weight,dilute concentration and high conductivity.Based on superfine PVDF nanofibers,a PVDF nanofiber membrane with multi-scale structure was constructed.Finally,its antibacterial properties were given by surface chemical modification.The specific research results are as follows:(1)The spinning solution system was systematically regulated by orthogonal experimental theory,PVDF solutions with different molecular weights and concentrations were configured,and the conductivity of the solution was regulated by the concentration of tetrabutyl ammonium chloride(TBAC).During the experiment,it was found that when the solution was in the state of dilute concentration and high conductivity,the needle was mainly spraying charged droplets.Based on this,according to the experimental results,a hypothesis(forming principle)is given,which is different from the traditional jet forming mode.In this state,the nanofiber film is obtained by drawing charged droplets into fine fibers and self-assembly.Based on this principle,superfine PVDF nanofiber membranes with good morphology,uniform distribution in the pore size of conventional nanofibers and diameter of 15-20 nm were prepared at 25 k V in a solution system with high molecular weight(600000),dilute concentration(3 wt%)and high conductivity(4.71 m S/cm).(2)Solve the problem that it is difficult to balance the filtration efficiency,filtration piezoresistance and light transmittance due to the close packing of a single scale,a nanofiber membrane with multi-scale structure was constructed with superfine PVDF nanofiber as the core,and the relationship between the structure and performance of multi-scale nanofiber membrane was balanced by adjusting the proportion of superfine and scaffold nanofiber.When the ratio is 1:1,the multi-scale PVDF nanofibers have pore size(0.72?m)Small and high porosity(92.22%).Thanks to this structural advantage,it shows excellent comprehensive performance,including PM_0.3 has high filtration efficiency(99.92%),low pressure resistance(69 Pa),good mechanical properties(28.17 MPa)and excellent hydrophobicity(122°).Based on this,we have also successfully applied it to the window screen.Under the weight of 0.72 g/m²,the window screen shows high transparency(?80%)and high air permeability(101 mm/s).The important thing is that it shows reliable practical performance.After 100 hours of ultraviolet irradiation,the filtration efficiency decreases by only 0.18%.After 10 cycles of treatment with water or alcohol,the interception efficiency of the window screen was 98.8%,and showed a significant effect on PM_2.5rapid repeated purification capacity.(3)Make nanofibers have higher value properties and meet the applications in more fields.PVDF-PAA-TMP-Cl nanofibers with haloamine antibacterial properties were obtained by hydroxylation of scaffold PVDF nanofibers,grafting polyacrylic acid(PAA)with 2,2,6,6-tetramethyl-4-piperidinol(TMP)by surface chemical modification,and then chlorination.Finally,on this basis,ultrafine nanofibers were spun to obtain PVDF-PAA-TMP-Cl nanofibers with multi-scale structure.The results showed that the morphology of the modified scaffold PVDF nanofibers basically did not change,and it could eliminate more than 98.5%of E.coli and S.aureus with a concentration of 10⁷ CFU/ml in about 3hours.Importantly,the modified PVDF nanofiber membrane with multi-scale structure also shows excellent filtration efficiency(99.85%)and low filtration pressure resistance(79 Pa).After three times of chlorination,it still has more than 90%antibacterial effect and has certain repeated antibacterial ability.Achieve good antibacterial performance without sacrificing filtration performance.