Preparation And Thermal-physical Properties Of Polyacrylic Acid Based Composite Phase Change Materials

Organic solid-liquid phase change materials have become the preferred materials for phase change media in the field of latent heat energy storage due to their high heat storage density,approximately constant phase change temperature and good stability.However,low thermal conductivity,easy leakage of liquid phase and pos sible corrosion during phase transition limit their large-scale applications.Porous carrier loading and shaping is the main way to solve the liquid phase leakage,increase thermal conductivity and improve thermophysical properties of solid-liquid phase change materials.However,the effect of coupling between phase change materials-carriers(host-guest)on the thermophysical properties of composite phase change materials is unclear.In view of this,polyethylene glycol(PEG),stearic acid(SA)and erythritol(ET)were used as phase change materials,Polyacrylate sodium(PAAS)and its carbide PAAS-C with three-dimensional porous network structure were used as carriers,and PAAS and PAAS-C composite phase change materials were prepared by solution impregnation and vacuum melting impregnation method,respectively,the morphology,structure and thermophysical properties of the composites were studied,and the influence of the surface properties of the carrier on the performance of the composites was explored.PEG/PAAS and PEG/PAAS-C composite phase change materials with PEG content of 67.88wt% and 60.86wt% respectively were prepared by using Water-soluble polymer PEG as phase change material,PAAS and PAAS-C as carrier.The results showed that there is only physical interaction between PEG and PAAS,PAAS-C,the melting latent heat of PEG/PAAS and PEG/PAAS-C is 124.52J/g and115.37J/g,respectively,and the solidification latent heat is 118.88J/g and 107.73J/g,respectively.The addition of PAAS with three-dimensional network structure not only makes PEG/PAAS have good shape stability and excellent cycle stability,but also increased its thermal conductivity from 0.1095W/m·K of PEG to 0.2029W/m·K.PAAS-C retains the original three-dimensional network structure of PAAS,but its pore size was increased,which leads to the decrease of latent heat and phase transition temperature of PEG/PAAS-C with the decrease of pore size of PAAS-C.At the same time,carbonization of PAAS is beneficial to alleviate the supercooling of PEG/PAAS and improve its thermal conductivity.The thermal conductivity of PEG/PAAS-C is 1.28 times higher than that of PEG / PAAS.SA/PAAS and SA/PAAS-C composite phase change materials with SA content of66.01wt% and 67.65wt% respectively were prepared by us ing hydrophobic SA as phase change material,PAAS and PAAS-C as carrier.The results showed that there is not only physical interaction but also intermolecular coupling between SA and PAAS,and the crystal structure of SA/PAAS is changed compared with SA.The unique pore structure of PAAS,the intermolecular coupling between PAAS and SA leaded to the layered crystallization of SA/PAAS,result ed in three exothermic peaks during the cooling process of SA/PAAS.The melting latent heat of SA/PAAS and SA/PAAS-C is129.12J/g and 132.33J/g,respectively,and the total solidification latent heat of the three exothermic peaks is 129.75J/g and 134.72J/g,respectively.The heat release rate of SA was accelerated and the supercooling of SA was improved by compounding with PAAS,SA/PAAS has good shape stability and cycle stability.In addition,carbonization at 600? and 800? removed some polar oxygen-containing functional groups in PAAS,which weakened the intermolecular coupling between SA and PAAS,resulted in only one exothermic peak of SA/PAAS-600 and SA/PAAS-800.ET/PAAS and ET/PAAS-C composite phase change materials with ET content of90.08wt% and 81.90wt% respectively were prepared by using water-soluble ET as phase change material,PAAS and PAAS-C as carrier.The results showed that there is only physical interaction between ET and PAAS,PAAS-C,which makes ET bound in PAAS,inhibits the liquid leakage of ET in the process of phase transition and ensures the good shape stability of ET/PAAS.The melting latent hea t of ET/PAAS and ET/PAAS-C is 312.65J/g and 284.23J/g,respectively,and the solidification latent heat is 182.18J/g and 143.62J/g respectively.There may be a non-solidified layer in the cooling crystallization process of ET/PAAS,which reduce d the exothermic capacity of ET/PAAS.It is helpful to improve the exothermic ability of ET/PAAS to keep the temperature below the crystallization poin t(50?)for 2 hours before cooling crystallization.The addition of PAAS not only increased the thermal co nductivity of ET/PAAS from 0.0836W/m·K of ET to 0.1242W/m·K,but also reduced the undercooling of ET,the undercooling of ET/PAAS decreases with the increase of ET content.In addition,PAAS-C increased the thermal conductivity of ET/PAAS by 1.73 times,and improved the supercooling of ET.