Preparation And Properties Of Thermal Conductive Reinforced Polyethylene Glycol Shape Stabilized Phase Change Composites

Phase change material(PCM)is a kind of environment-friendly material that stores and releases energy through endothermic and exothermic processes.It mainly realizes the purpose of thermal management and energy saving through thermal energy storage and temperature regulation.It can be widely used in textile,intelligent electronic equipment thermal management,waste heat recovery,solar energy utilization,building thermal management,aerospace and other fields.Polyethylene glycol(PEG)is the most common solid-liquid phase change material because of its wide phase transition temperature,high latent heat,good chemical stability,low vapor pressure,non-toxic and low price.However,the low thermal conductivity of PEG reduces the energy storage efficiency and thermal regulation performance;at the same time,PEG is prone to leak in the process of phase transition.Low thermal conductivity and easy leakage limit the application of PEG in practice.Therefore,how to prepare PEG phase change composites with high thermal conductivity and stable shape has become a research hotspot at home and abroad.For the above defects of PEG,the following three parts are carried out in this paper.(1)The preparation,thermal conductivity,phase transformation and crystallization behavior of micro nano flake boron nitride filled PEG composites were studied.Based on PEG,adding BN thermal conductive fillers with different sizes(0.5 ?m,5 ?m,50 ?m respectively),PEG / BN thermal conductive phase change composites were prepared by melt blending casting method,and the effects of BN thermal conductive fillers with different sizes on the thermal conductivity and crystallization properties of PEG were investigated.The results show that the large BN filler can improve the thermal conductivity of PEG phase change composites more effectively,and the thermal conductivity of the composites can reach 5.04 W/(m·K)when the BN(50 ?m)content is40%.At the same time,according to the non isothermal kinetic analysis,50 ?m BN can more effectively induce the crystallization of PEG.At a higher cooling rate,the BN filler with 50 ?m sheet diameter can shorten the half crystallization time of phase change composite,improve the crystallization rate of phase change composite,and make the phase change composite have a larger phase change enthalpy.(2)This chapter introduces expanded graphite(EG)and epoxy resin(EP).Firstly,PEG/EG blends were prepared by vacuum adsorption method,and then low filling and high thermal conductivity phase change composites were prepared by melt blending method.The phase change stability and phase change energy storage characteristics of the composites were studied,and the formation of internal thermal conduction pathway and thermal conduction mechanism of the composites were deeply analyzed.The experimental results show that the porous structure of EG,the three-dimensional crosslinking network of EP and the sheet structure of BN can synergistically prevent the leakage of PEG during the phase transition process,which makes PCMs have excellent anti leakage performance and good cycle stability.At the same time,under the condition of low filling(EG = 3.36 Vol%,BN = 9 Vol%),EG and BN can form a good dual continuous thermal conduction path in the PCMs sample,which makes the composite show excellent thermal conductivity with a thermal conductivity of 3.91 W/(m·K),high phase change latent heat(79.93 J/g),and good phase change thermal conductivity.(3)Nano cellulose(CNF),a renewable resource,was used instead of epoxy resin(EP)to prepare phase change composite films by solution blending.The forming process of the composite film and the structural morphology of PEG in the composite film were studied,and the composition ratio of the composite film with high thermal conductivity was further optimized.The phase change energy storage behavior and anisotropic thermal conductivity of the composite films were studied.The experimental results show that the prepared film has good flexibility.When the EG content is 7% and BN content is 15%,the in-plane thermal conductivity of the films is 10.83 W/(m·K),and the out-of-plane thermal conductivity is 1.60 W/(m·K),and a high latent heat(79.46 J/g)was maintained.At the same time,the phase change film has good phase change stability without leakage after heating at 100 ? for 5 h.