Preparation And Application Of Radiative Cooling Fiber

Comparing with the traditional fabric,the radiative cooling fiber can reflect the solar radiation and transfer heat to outer space in the form of infrared radiation.To achieve passive radiative cooling effect,the fiber requires relatively high reflectivity in the short band reflectance（200-2500 nm）and high emissivity in the mid infrared band,especially atmospheric window（8-13μm）.In this dissertation,Mg₁₁（HPO₃）₈（OH）₆,SiO₂ and related inorganic powders were compounded with polymer matrix materials by electrospinning and melt spinning technology,and the fibers with excellent radiation cooling performance were directly prepared.XRD,SEM,UV Vis NIR and FT-IR were used to characterize the structure,micro-morphology,reflectivity and emissivity of the fiber.The theoretical explanation of high reflectivity and emissivity was proposed.The main results are as follows:（1）Composite fibers with high short-wavelength reflectivity and mid infrared emissivity were synthesized by electrospinning.When the thickness is about 300-400μm,the reflectivity of the electrospun PMMA/PS/PVDF fiber reaches 96%at 200-2500nm.The difference of molecular structure leads to the dissimilarity of emissivity of different substrates.PVDF shows best selective emissivity in the atmospheric window（74.71%）.Grooved PMMA fibers were prepared by adjusting the ratio of DMF/DCM in the spinning solution,the emissivity increased rapidly from 62.05%,55.85%to 72.44%78.85%,respectively.（2）In the composite fiber,the type of inorganic particles determines its short band scattering and mid infrared absorption capacity.Mg₁₁（HPO₃）₈（OH）₆ particles with micro nano-needle structure on the surface and extensive infrared molecular vibration absorption types is the best inorganic fillers.The emissivity of the composite fiber is not linear with the content of inorganic particles,and the optimal doping ratio is 5%.The inducing broad-spectrum resonance absorption by inorganic particle combined with the molecular bond resonance absorption in the composite fiber makes the emissivity of Mg₁₁（HPO₃）₈（OH）₆-PMMA fiber increase rapidly from62.05%,55.85%to 90.27%,84.59%.（3）Pure pp fiber was prepared by melt spinning.The composite fiber was prepared by stearic acid modified hydrophobic SiO₂,Mg₁₁（HPO₃）₈（OH）₆ particles and pp.When the content of SiO₂ in the composite fiber exceeds 5%,the surface roughness of the fiber increases and the glossiness decreases.The diameter of single pipe is 50μm.The results show that the transmittance of pp fiber outnumbers 90%.The crystal area with crystal size of more than 20nm and crystallization rate of about 50%,inorganic particles distributing in the fiber both together reducing the transmittance of the composite fiber.Compared with spherical SiO₂particles,acicular Mg₁₁（HPO₃）₈（OH）₆ has larger surface area and higher spectral performance.Compared with pp fiber,the reflectivity of Mg₁₁（HPO₃）₈（OH）₆-pp composite fiber increased by3.3%and 4%at 200-380 nm and 200-2500 nm,respectively.The broad-band resonance absorption induced by Mg₁₁（HPO₃）₈（OH）₆ in the mid infrared band significantly improves the emissivity of the fiber,reaching 81.06%and 88.41%respectively.（4）In the case of direct sunlight in the daytime,the results of actual outdoor cooling test of radiation cooling fiber shows that 5wt%Mg₁₁（HPO₃）₈（OH）₆-pmma fiber and Mg₁₁（HPO₃）₈（OH）₆-pp fiber can achieve cooling effect of 2～4℃and 1～2℃lower than air temperature respectively.It is found that both the mid infrared pp fiber and the mid infrared high emission Mg₁₁（HPO₃）₈（OH）₆-pmma fiber can conduct heat from human body.