Preparation And Performance Optimization Of Polyethylene Glycol/Chitosan Based Composite Phase Change Materials

Polyethylene glycol（PEG）is a kind of organic solid-liquid phase change material with excellent properties,such as non-toxicity,good chemical stability,and high heat storage density.In its practical application,PEG usually needs to be encapsulated to avoid the leakage during the process of its solid-liquid phase transformation.Chitosan（CS）is a kind of natural polymer material,which might be used as a supporting material for PEG,for it has abundant functional groups and long chain structure.To obtain PEG/CS composite phase change materials of high performances,the factors affecting the heat storage performance of polyethylene glycol/chitosan solid-solid phase change materials（PEG-CS）were systematically studied.Meanwhile,a new polyvinyl alcohol/chitosan dual network（PVA/CS）with heat storage ability was established for the first time.Subsequently,the thermal conductivities of the prepared samples were improved,and the corresponding composite phase change materials were obtained by vacuum impregnation,using the prepared aerogels as the porous substrates for encapsulating PEG.This study would provide new foundation for the application of CS and PEG in the field of composite heat storage materials.The main research contents are as follows:（1）Aldehyde PEG（OHC-PEG）and amino PEG（H₂N-PEG）were prepared respectively by modifying PEG,and then two polyethylene glycol/chitosan solid-solid phase change materials（C-PEG-CS and N-PEG-CS）were prepared correspondingly,after chemical crosslinking of the modified PEG with CS.Factors that influence the heat storage properties,thermal stabilities and shape stabilities of C-PEG-CS are discussed in detail.The results show that the temperature range and enthalpy of the phase transition of C-PEG-CS can be adjusted by varying the molecular weight of PEG.As the mass ratio of OHC-PEG to CS increases,the heat storage ability of C-PEG-CS would be increased.Increasing the concentration of OHC-PEG and CS will decrease the heat storage efficiency of the prepared C-PEG-CS,but can make the pore structure of C-PEG-CS to be conducive to PEG encapsulation.N-PEG-CS was synthetized using H₂N-PEG,and has a heat storage efficiency of 78.1%.（2）To further optimize the heat storage performances of C-PEG-CS and N-PEG-CS,a PVA/CS dual network was constructed,and two kinds of phase change materials,PC and PN,with excellent performances,were prepared for the first time.The effect of PVA mass fraction on the thermal storage performances of PC and PN were studied.The results show that,with the increase of PVA mass fraction,the physical binding effect of PC to PEG will be improved.Thus,the heat storage ability of PC has been increased,and it could be 7.6%higher than that of C-PEG-CS.Similarly,the addition of PVA improved the heat performances of N-PEG-CS.Compared with N-PEG-CS,the heat storage efficiency of PN has increased by 11.9%.For PC aerogel has reasonable pore structure,PEG@PC composite phase change material could have a heat storage efficiency of nearly 100%after further encapsulation of PEG of PC aerogel.（3）Aerogel with heat storage ability can be used as the porous carrier for PEG.To further optimize the thermal conductivities and mechanical properties,carbon nanotubes（MWCNTs）and graphene oxide（GO）were added to C-PEG-CS system and PVA/CS dual network,respectively,and CC and CG aerogels and PCC and PCG aerogels were obtained,correspondingly.After vacuum impregnation of PEG,PEG@CC4 and PEG@CG1 were obtained.The characterizations show that,at 60%strain,the compressive strengths of CC and CG aerogels could reach 2.952 MPa and0.678 MPa,respectively.PEG@CC4 and PEG@CG1 both had excellent heat storage properties.The melting and solidification enthalpies of PEG@CC4 were 157.0 J/g and131.7 J/g,respectively,corresponding to a heat storage efficiency of 91.0%.The melting and solidification enthalpy of PEG@CG1 was 171.2 J/g and 153.9 J/g,respectively,and its heat storage efficiency is 99.2%.The thermal conductivity of PEG@CC4 and PEG@CG1 is 2.82 times and 1.15 times of that of pure PEG,respectively,which indicates that they have excellent thermal conductivity.The additions of MWCNTs and GO to PVA/CS dual network,have not achieved the desired effects due to the agglomerations of the carbon materials.