Design And Preparation Of Passive Cooling Composite Materials

In order to solve the problem of excessive energy consumption of building refrigeration in the world,two kinds of materials with different passive cooling modes are prepared in this topic,namely,hydrogel material for passive evaporative cooling and multi-layer fabric material for passive radiation cooling.During high temperatures,these two materials cover the surface of the building,allowing cooling without the need for outside power input.The use of passive cooling materials can not only effectively save the global building refrigeration power resources,but also reduce the greenhouse gas emissions generated by air conditioning and other refrigeration equipment,which is also of great significance to alleviate global warming.Alginate-Ca²⁺/PNIPAM hydrogel with interpenetrating network structure was successfully prepared by adding Alginate component into poly N-isopropylacrylamide（PNIPAM）gel,and it was loaded onto cotton fabric（Cotton-IPN）.The passive evaporative cooling material was characterized by scanning electron microscope,infrared spectroscopy,swelling ratio test,hygroscopicity test,cycle test and cooling test.The results showed that the swelling rate of alginate-Ca²⁺/PNIPAM hydrogel with Alginate component decreased from 6.45g/g to 5.24 g/g,but the hygroscopic rate increased from 0.17 g/g to 1.71 g/g,compared with pure PNIPAM hydrogel.The hygroscopicity remains unchanged after ten cycles of testing.In addition,alginate-Ca²⁺/PNIPAM hydrogel has excellent flexibility and structural strength.In indoor simulated cooling test,the cooling effect of 5.88 mm thickness Cotton-IPN can reach15.3℃,and the continuous cooling time is about 4.5 h.In outdoor cooling tests,the cooling effect of 5.88 mm thickness Cotton-IPN can still reach 13℃,but the continuous cooling time is reduced to about 3.5 h.For a medium-sized home,a roof covered with Cotton-IPN is expected to reduce electricity consumption or carbon dioxide emissions by 55%per year.The passive radiative hydrophobic multilayer fabric cooling material（PPC）prepared in this paper mainly consists of three layers.The top layer of polydimethylsiloxane film（PDMS）is the main contributor to the emissivity,the middle layer of polymethyl methacrylate film（PMMA）is the main contributor to the reflectivity,and the bottom layer of cotton fabric mainly plays an important role in support and protection.The PPC materials were characterized by scanning electron microscopy,infrared spectroscopy,contact Angle test,self-cleaning test and cooling test.The results show that the PPC material has a rich convex and uneven filament structure and ideal internal bonding structure,which can achieve a high enough solar reflectivity（94%）and a high atmospheric window emissivity（79%）.The top layer of PPC material is hydrophobic,and the contact Angle of water can reach 118°.The dripping water will roll on the surface of the inclined PPC material,thereby taking away most of the contaminants.In the outdoor cooling test,PPC material has excellent cooling ability,and the cooling effect is about 7.8℃.For mid-size homes,roofs covered with PPC materials are expected to reduce electricity consumption or carbon dioxide emissions by 18%per year.