Preparation And Thermal Properties Performance Analysis Of Polymer Shape Stable Solid-solid Phase Change Materials

Currently,the demand for sustainable energy storage increased rapidly in recent decades due to is a significant gap in energy generation and storage.Thus,recent efforts have focused on the development of new energy storage technologies to meet the needs of accelerating technological progress.Phase change materials(PCMs)have been widely applied in many applications,including aerospace,building energy,solar energy utilization,and the textile industry.Among other PCMs,organic PCMs are chemically and thermally stable,without phase segregation after repeated cycling,polyethylene glycol(PEG)is one of the most promising solid-liquid PCMs are promising because of their high latent enthalpy,wide transition temperature range,and cheap.Nevertheless,the thermal conductivity of organic PCMs is typically low,and in the molten state is not stable to cause leakages for PCM composites.Therefore,solid-solid PCMs have shown unique advantages such as no leakage,stable shape,and good performance of phase change cycle could overcome the above limitation of solid-liquid.In this dissertation,sustainable PCMs were successfully fabricated using polyethylene glycol(PEG)and polyhexadecyl acrylate(HDA)as non-toxic and non-polluting phase change functional materials into polyvinyl alcohol(PVA)matrix.Besides factionalized cellulose nanocrystal(CNC)was added as supporting framework materials for PCMs.The effect of fabrication technique(mechanical-physical blending and chemical crosslinking)on the PCMs structure and properties were discussed in detail.The changes of corresponding microstructure,chemical structure,thermal stability,and phase change properties of solid-solid phase change materials were thoroughly studied under different experimental conditions.The main research contents are summarized as follows:(1)Electrospun polyethylene glycol/polyvinyl alcohol composite nanofibrous membranes as shape-stabilized solid-solid phase change material:A shape-stable solid-solid phase change material(SSPCM)with PEG as phase change medium and PVA as supporting material was prepared by electrospinning method.Thus,PEG encapsulated by PVA was achieved due to the strong hydrogen bond and physical entanglement between the PEG and the PVA molecular chain.The morphology and structure of the prepared fibers were studied by SEM.The results showed that the PEG/PVA composite membrane fibers had nanostructure with the size of440±40 nm.Then,the phase transformation properties of PEG/PVA composite films were studied by DSC.The results showed that the heat storage capacity of the composite films increased with the increase of PEG content,and the enthalpy of PEG/PVA=7/3 was as high as 78.81 J/g.In addition,the composite fiber had good thermal stability,melting enthalpy and crystallization enthalpy showing no obvious change after 100 times of heating and cooling cycles.Overall,the preparation process of simple electrospinning method was used,and the raw material of solid-solid phase change material was low-cost and good thermal stability,showing the SSPCM great application potential in intelligent textile and energy storage system.(2)Poly(hexadecyl acrylate)/cellulose nanocrystal solid-solid phase change material were prepared by in-situ free radical polymerization:SSPCM with poly(hexadecyl acrylate)(PHDA)as phase change medium and silane modified cellulose nanocrystals(CNC)as skeleton material was prepared by in-situ free radical polymerization.Specifically,reactive vinyl was first grafted onto cellulose nanocrystals(CNC-VTMS),and then polymerized with PHDA as a reactive site.PHDA was immobilizing to CNC-VTMS by grafting and intermolecular force,and CNC-VTMS could act as nucleating agent to promote crystallization.SEM analysis results confirmed that PHDA was successfully fixed on the CNC-VTMS.The crystallization properties of SSPCM were studied by XRD,and the corresponding data showed that CNC-VTMS could promote the crystallization properties of grafted PHDA.The phase transformation performance of SSPCM was investigated by DSC.The results showed that SSPCM exhibits good thermal stability and high melting enthalpy(139.70 J/g),which was much higher than that of pure phase change energy storage unit(85.18 J/g).After 100 heating and cooling cycles,the melting enthalpy and crystallization enthalpy of SSPCM did not change significantly,which indicated that SSPCM has excellent thermal reliability and phase transformation performance.In addition,the prepared SSPCM also had excellent thermal stability(T_max=355?),which provided enlightenment for the wide application of solid-solid phase change materials in thermal management and energy storage systems.