Study On Preparation And Properties Of Sugar Alcohol/hollow Kapok Fiber Phase Change Composites

Organic phase change materials?PCMs?have the defects of poor thermal conductivity and easy leakage of liquid phase in the process of heat and cold cycles,which limit their practical application in the field of energy storage.Kapok fiber?Kf?has a natural hollow tubular structure.This unique morphology can effectively encapsulate organic phase change materials and provide a large storage space.As a green,natural and degradable porous carrier,it has potential application prospects to prepare organic phase change composites.In this paper,porous kapok fiber biomass carbon materials,kapok fiber biochar materials such as manganese dioxide nanowires and kapok fiber based aerogels were used as support carriers.D-mannitol?Man?and erythritol?Ery?with high latent heat value were used as organic phase change materials,and a series of composite phase change materials were prepared by vacuum melting impregnation by capillary force.In order to improve the thermophysical properties and stability of solid-liquid composite phase change materials.The main contents of this paper are as follows:In the first part,the carbonized porous biomass kapok fibers were used as support materials to compound with organic phase change materials D-mannitol?Man?and erythritol?Ery?,respectively,to prepare composite phase change materials.The results of SEM and TEM show that secondary channels are formed on the outer wall of hollow tubular kapok fibers after KOH etching,which provides good conditions for the transmission and storage of phase change materials.BET test results show that the specific surface area of KKf of kapok fibers after KOH etching is as high as 3396m²g^-1;DSC test results show that the composite phase change materials have good storage.The latent heat values of Ery/KKf and Man/KKf are 322.46 J g^-11 and 297.84 J g^-11 respectively,and the latent heat value of Ery/KKf is 298.54 J g^-11 after 250 cycles of cooling and heating.In addition,the supercooling degree of glycol is reduced due to the introduction of kapok fiber.TGA tests show that the composite phase change materials have good thermal resistance because they are not completely decomposed at 800 ^o C.The thermal conductivity of the composite phase change materials can be measured by flash thermal conductivity meter.The experimental results show that the thermal conductivity of the composite phase change materials is increased by 131%-133%compared with that of the pure phase change materials.The second part:after the initial treatment of kapok fibers and manganese dioxide nanowires were mixed evenly,the carrier Ckf-MnO₂ was prepared by carbonization in a tubular furnace.The composite phase change materials were obtained by compounding with D-mannitol and erythritol.SEM and TEM show that the carbonized kapok fibers and MnO₂ nanowires retain the tubular structure and overlap each other in a network shape,which has a high loading rate for organic phase change materials.DSC analysis show that the latent calorific values of Man/Ckf-MnO₂ and Ery/Ckf-MnO₂ are 300.39 J g^-11 and 312.74 J g^-11 respectively.After 250 cycles,the loading rate of Man/Ckf-MnO₂ composite phase change materials is still as high as 88.96%,and their latent calorific values are 286.33 J g^-1.The results of TGA test illustrate that Ckf-MnO₂ as carrier decomposed only 4.34%at800 ^o C and the composite phase change materials did not decompose completely,which indicate that the composite phase change materials have good stability.Compared with pure organic phase change materials,the thermal conductivity of D-mannitol and erythritol have increased by 216%and 209%,respectively.The third part:adding sodium alginate into kapok fiber and preparing kapok fiber based aerogel?CNF?containing different proportion of sodium alginate,which is combined with organic phase change material D-mannitol and erythritol,obtains kapok fiber based aerogel composite phase change material.SEM morphology observed that phase change materials were completely filled in the layered space of kapok fiber aerogels,and the more proportion of sodium alginate added to kapok fiber aerogels,the more dense layered arrangement appeared.Strain stress experiments showed that kapok fiber based aerogels had good mechanical properties,and aerogels showed better mechanical properties as the proportion of sodium alginate increased.DSC analysis showed that the load rates of Man/0.5%-CNF,Man/1%-CNF,and Man/1.5%-CNF were 70.36%,73.59%and 80.22%,respectively after 250 cycles,and the latent calorific values were 226.46 J g^-1,236.86 J g^-11 and 258.20 J g^-1,respectively.The TGA test showed that 37.67%of CNF remained undecomposed at 800 ^o C,indicating that the carrier kapok based aerogel possessed good thermal stability.