Preparation And Radiation Cooling Performance Of Thermal Comfortable Mask Material For Preventing PM_2.5

Masks are the most widely used human respiratory protection products.They can significantly reduce the harm to human body and public health caused by fine particle(PM_2.5)pollution and the spread of bacteria and viruses in form of aerosols and droplets.However,at present,the commercial high-efficiency protective masks make the wearers have a sense of facial sultry,especially in high-humidity environments for a long time.It greatly limits the promotion and use of personal respiratory protection devices,and is not conducive to improve the capabilities of public health prevention and control.Therefore,the radiation cooling,a zero-energy surface cooling technology was used in this study for the thermal management of mask filter materials.The PA6-TiO₂ composite filter materials with thermal comfort and superior PM_2.5 caption function were prepared by electrospinning.And their infrared transmission and visible opacity mechanisms were explored by the Mie scattering theory and finite-difference time domain(FDTD)numerical simulation.First,the infrared-transparent PA6 nanofiber filter material was prepared by the electrospinning.The arrangement of PA6 fibers and the pores of the filter materials were adjusted by controlling the electric field distribution during electrospinning.The prepared PA6fiber filter has low respiratory resistance(49 Pa@5.3 cm/s),high PM_2.5 capture efficiency(>99%)and high human infrared heat radiation transmittance(>88%).In an indoor environment of 25.3°C,the face surface temperature when wearing a PA6 filter mask was 1.5°C and 1.7°C lower than wearing that of a disposable mask and a N95 mask,respectively.Then,the Mie scattering theory was employed to calculate and analyze the infrared radiation characteristics of the electrospun PA6 fiber filter.The optical constants and radiant thermal conductivity(3.076 mW·m^-1·K^-1)of the PA6 fiber filter were calculated,and the influence of fiber diameter and volume fraction on the infrared transmission of the filter were explored.It is found that reducing fiber diameter or volume fraction can improve the infrared transmittance,but it also reduces the PM_2.5 capture performance.Next,the TiO₂ particles with high refractive index were added for preparing the PA6-TiO₂composite fiber filter with infrared transmission and visible opacity.The size,mass fraction,surface morphology,crystal type of the TiO₂ particles were investigated for the composite filter materials'visible light transmittance and the radiant cooling performance.It is found that the addition of 1.1 wt%sub-micron flower-like TiO₂-rutile particles can maximize the visible light blocking performance of the fiber filter.The PA6-TiO₂(flower)filter material had a pore size range of 50?1000 nm,which is equivalent to the wavelength of visible light.Its transmittance of visible light(300?800 nm)is 71.7%,which is 15.45%lower than that of pure PA6 filter material,while its infrared transmittance is still higher than 85%.The PA6-TiO₂ composite filter had a filtration efficiency of 94%for PM_2.5,the breathing resistance as low as 22 Pa,a water vapor transmission rate of 0.0169 g/cm²/h.Finally,the FDTD method was used to simulate the transmission performance of the PA6-TiO₂ composite fiber filter in the infrared and visible light bands,which revealed the transmittance of radiant heat inside the fiber along the thickness direction.It is proved that when adding the same volume fraction of TiO₂,increasing the size of TiO₂ particle can enhance the PA6-TiO₂ material's ability to block the visible light.