Preparation And Performance Of Cellulose And Polymethylmethacrylate-based Radiative Cooling Materials

Residential buildings around the world consume a lot of energy every year,a large part of which comes from building cooling and air-conditioning systems.In order to reduce energy consumption and the resulting environmental pollution,a new cooling technology is urgently needed.Radiative cooling is a new technology which realizes cooling only on the basis of material properties and special structure in the absence of external energy input.In this paper,wide-sized particles such as calcium silicate and zirconia were randomly distributed in cellulose acetate and other polymer materials to form the final composite film by using the processes of phase separation and electrospinning.In this paper,the structure and properties of the material are studied in detail:1.The film was prepared by casting-phase inversion process with low-cost cellulose acetate and calcium silicate as raw materials.The effects of many factors on the comprehensive solar reflectivity and emissivity of the films were studied,such as the porosity produced in the process of phase separation,the addition amount of calcium silicate,the thickness of the composite film,the size distribution of calcium silicate and so on.The wide-size distribution of calcium silicate particles and micropores effectively reflect the full-band sunlight,making the reflectivity of the film up to 97.3%.The Si-O bond in calcium silicate,the O-H bond and C-O bond in cellulose have strong infrared absorption in the atmospheric window,resulting in an emissivity of 97.2%of the composite film.When the solar light intensity is 803～885 W·m^-2,the film shows a sub-ambient temperature drop up to 7.3℃ and an average net cooling power of 90.7 W·m^-2.2.A kind of coating suitable for various complex surfaces was prepared with polymethylmethacrylate（PMMA）as polymer binder and calcium silicate with wide band gap as filler particles.The effects of the volume concentration of calcium silicate particles,the thickness of coating layer and the size distribution of calcium silicate particles on the reflectivity of the coating were studied.The comprehensive reflectivity of the coating in the solar band is 96.4%,and the emissivity in the atmospheric window band is 97%.The wide size distribution and high volume concentration of calcium silicate particles make the coating reflect sunlight effectively.The Si-O bond in calcium silicate has a strong absorption of infrared light near 10μm.The stretching vibration of C-O-C bond in PMMA results in obvious infrared absorption at 8.6μm,10μm and 11.8μm,so the coating has high emissivity in the atmospheric window band.When the solar light intensity is 502～568 W·m^-2,the film shows a sub-ambient temperature drop up to5.8℃ and an average net cooling power of 74.2 W·m^-2.3.In addition,a kind of flexible polymer film was obtained by electrospinning with PMMA as polymer substrate and inorganic nanoparticles Zr O₂/Zn O.The effects of the amount,type and size distribution of inorganic nanoparticles on the reflectivity of the films were studied.Through the comparison of reflectance,it is concluded that the film containing Zr O₂ particles has better properties.The abundant pores between the polymer fibers and the large band gap of Zr O₂ particles endows the film with a high reflectance of 97.7%in the solar band.At the same time,PMMA has several vibration absorption peaks in the atmospheric windows,which makes the emissivity of the film reach 86.7%.When the solar light intensity is 591～637 W·m^-2,the film shows a sub-ambient temperature drop up to 5.4℃ and an average net cooling power of 62.6 W·m^-2.