Study On The Preparation And Thermal Conductivity Of New Shaped Phase Change Materials

For the promble of leakage and low thermal conductivity of polyethylene glycol（PEG）solid-liquid phase materials,a series of composite phase change materials with stable shape and good thermal conductivity are prepared by grafting and polymerizing PEG onto the"hard segment"skeleton of macromolecules and adding thermal conductivity enhancement agent in this paper.The specific research contents are as follows:（1）A series of composite phase change materials(PCM_MHP)with stable shape and good thermal conductivity are prepared by using PEG as phase change molecular chain,hydroxypropyl cellulose（HPC）as macromolecule"hard segment"skeleton,and MWCNTs as thermal conductivity enhancement agent.PCM_MHPexhibit good shape stability and hold at 353.2 K for an hour without leakage.The melting and freezing enthalpy of PCM_M1HP7 are134.7 J·g^-1 and 131.2 J·g^-1,respectively;corresponding to melting point and crystallization temperature as 323.59 K and 306.01 K respectively.The results indicate that the PCM_MHPhas a good reversible thermal stability after 100 heating/cooling cycles.And as adding MWCNTs to 4 wt%,the thermal conductivity of PCM_MHPreaches to 0.6019 W·m^-1·k^-1,which is 1.9 times that of pure PEG.（2）In order to simplify the experiment and make the preparation process safer and more environmentally friendly,a new shaped type of polyethyleneimine/polyethylene glycol（PP）composite phase change material is successfully synthesized by usingγ-glycidyl ethoxytrimethoxysilane（KH-560）as the cross-linking agent and polyethyleneimine（PEI）as the curing agent.And the preparation process does not require the introduction of nitrogen gas and the use of organic solvents.The overall performance of PP₇ is the best as the addition amount of PEG is 70 wt%;and its melting point/melting enthalpy and crystallization temperature/crystallization enthalpy are 325.01 K/128.8 J·g^-1 and 305.94 K/121.0 J·g^-1,respectively.After 100 heating/cooling cycles,the change value of phase change enthalpy of PP₇ is lower than 2.3 J·g^-1,which proves that PP₇ has good phase change heat storage characteristics.（3）PEG is successfully grafted onto the hydroxylated carbon nanotubes by chemical grafting with KH-560 modified hydroxylated carbon nanotubes as curing agent and PEG as phase change material to obtain a novel shaped phase change material of polyethylene glycol/hydroxylated carbon nanotube（PPC）.And the KH-560 modified hydroxylated carbon nanotubes can be used as both a curing agent and a thermal conductivity enhancer.The latent heat of phase change for PPC is in the range of 119.9～127.9 J·g^-1,and the phase transformation temperature is in the range of 311.68～330.86 K.Moreover,PPC exhibits good thermal cycling stability after 100 heating/cooling cycles.The thermal conductivity of the PPC is 0.7081 W·m^-1·k^-1as the addition of hydroxylated carbon nanotubes is 9 wt%,which is 2.2 times of pure PEG thermal conductivity.And after thermal cycling,the hydroxylated carbon nanotubes modified by KH-560 can still be uniformly dispersed in PPC.