Preparation Of PAN/SiO₂@PU Shell-core Composite Nanofiber Membranes For Waterproof And Breathable Properties

Electrospinning nanofiber membrane is considered as a potential waterproof and permeable material due to its high porosity,small pore size and adjustable pore structure.There are still some problems in the preparation of composite fiber membrane by physical blending of inorganic nanoparticles and polymer,such as embedding of particles in the fiber,inadequate performance and poor mechanical properties of the obtained fiber membranes.Coaxial electrospinning can be used to load inorganic nanoparticles in the shell layer,which can not only ensure the continuity of the core material,but also increase the surface roughness of the fiber by making nanoparticles located on the fiber surface as much as possible to improve the material hydrophobicity.Therefore,in this paper,PAN/SiO₂@PU composite nanofiber membranes with excellent waterproof and moisture permeability were prepared by coaxial electrospinning technology with polyurethane（PU）as the core solution and polyacrylonitrile/SiO₂（PAN/SiO₂）as the shell solution.The effects of the feeding rate ratio of the shell solution and the core solution,the content of SiO₂ in the shell solution,and the hydrothermal time on the composite nanofiber membrane were analyzed.In this paper,SiO₂ nanoparticles were prepared by hydrothermal method combined with St?ber method.The effect of hydrothermal time on the particle size of SiO₂particles was studied.The results showed that when the hydrothermal time was 30 min,the SiO₂ particles had a minimum diameter of 32 nm and uniform size.In addition,the concentrations of PU solution and PAN/SiO₂ solution in separate electrospinning were investigated.The results showed that when the PU concentration was 18%and the PAN concentration was 14%,the fiber diameter in the PU fiber membrane and the PAN/SiO₂fiber membrane was uniform,without the beaded structure.Then,SiO₂ particles were loaded on the shell PAN fibers by coaxial electrospinning.The shell-core structure of the fibers in the PAN/SiO₂@PU composite nanofiber membrane was regulated by regulating the feed rate ratio of the shell-core solution during spinning.The microstructure,the waterproof and moisture permeability and mechanical properties of the fiber membrane were studied.The results showed that when the shell-core feed rate ratio was 5:1,the fiber diameter in the membrane was uniform and it exhibited a good shell-core structure.At this time,the content of Si element on the surface of the fiber membrane was the higher（1.3%）,the water contact angle was 137°,the water vapor transmission rate was 7.3 kg·m²·d^-1,the broken strength was 5.23 MPa,and the broken elongation was 60%.In order to improve the hydrophobic properties of PAN/SiO₂@PU composite nanofiber membranes,the content of SiO₂ in the shell solution was further studied.The effect of adding SiO2 on the microstructure,surface roughness,surface Si contents,waterproof and moisture permeability and mechanical properties of PAN/SiO₂@PU composite nanofiber membrane was studied.The results showed that when the content of SiO₂ in PAN solution was 60 mg/m L,the fiber membrane had uniform diameter,the larger surface roughness（70 nm）,the larger surface Si element content（3.5%）,uniformly distributed SiO₂ particles and the better hydrophobic property（water contact angle was 139°）.At this time,the water vapor transmission rate was 8.2 kg·m²·d^-1.Superhydrophobic PAN/SiO₂@PU composite nanofiber membranes were prepared by hydrothermal method using hexadecyltrimethoxysilane（HDTMS）alcohol solution.The microstructure,waterproof and moisture permeability of the nanofiber membranes were studied.The results showed that when the hydrothermal time was 2 h,the membrane had superhydrophobicity（water contact angle was 152°,rolling angle was 9°）and good moisture permeability,and the water vapor transmission rate was 8.48kg·m²·d^-1,and the water vapor transmission rate was 8.48 kg·m²·d^-1.In order to broaden the application field of hydrophobic fiber membranes,the effect of PAN/SiO₂@PU composite nanofiber membranes on light was studied.The results showed that the average reflectance of the composite nanofiber membrane to sunlight was 60.29%.Compared with the PAN@PU composite nanofiber membrane under the same radiation conditions,the temperature difference was 4.5℃,which was not sensitive to sunlight and can be used in the field of radiation cooling.