Construction And Properties Of Polyethylene Glycol Phase Change Energy Storage Composites With High Photothermal Conversion

With the increasing energy demand,the development of renewable energy can improve the energy structure,in line with the concept of green sustainable development.Improving energy utilization is also an inevitable choice to solve the energy shortage and pollution.Solar energy is the most widely distributed and abundant form of renewable energy.Its inexhaustible nature makes the development and utilization of solar energy become one of the main components of future energy strategy.However,regional,diurnal and climatic factors make solar energy cyclical and unstable.Phase change energy storage technology relies on phase change materials（PCM）to absorb/release thermal energy while changing the state of material during the phase change process.Therefore,under sufficient solar radiation,PCM can store the solar energy in time,and release the stored heat when the solar radiation is insufficient.This is expected to improve the problem of solar energy periodicity and instability and realize the effective utilization of solar energy.Most PCM have limited visible light absorption capacity for solar radiation.Therefore,it is necessary to develop composite PCM with high thermal storage capacity and high photothermal conversion efficiency under solar radiation.Polyethylene glycol（PEG）,a typical organic PCM,has been extensively studied due to its weak light absorption,strong rigidity,and poor shape stability in applications.In this paper,carboxyl carbon（RHTC）with light absorption capacity was used as the packaging material,boron nitride（BN）was used as the heat conductor,and poly（acrylamide-co-acrylic acid）（PAAAM）,melamine sponge（MF）,and polyvinylidene fluoride（PVDF）were used as supporting materials,respectively.A series of phase change composites with stable shape,high photothermal conversion,and thermal storage capacity were prepared.The influence of composition,structure,morphology,and properties of the prepared composites was discussed.The main research contents are as follows:1.RHTC functionalized by acrylic acid（AA）with light absorption capacity was prepared using glucose(C₆H₁₂O₆)as the carbon source.The surface carboxyl content of RHTC was 5.5 mmol/g.RHTC/PEG were prepared using RHTC as photothermal conversion agent.when RHTC content is 3 wt%,the photothermal conversion storage efficiency of RHTC/PEG is as high as 90.1%,the latent heat capacity is up to 169.2 J/g,which is 10.7 J/g higher than pure PEG.However,the weak interaction between PEG and RHTC,RHTC/PEG composites have certain leakage at high temperatures,which is more suitable for below 62°C.2.To solve the high-temperature instability problem of RHTC/PEG composites,PAAAM was used as the supporting material.The free radical copolymerization method can realize the successful coating of PEG or RHTC/PEG while forming PAAAM.PAAAM can inhibit PEG crystallization,but the diffraction peak of PAAAM/RHTC/PEG is obviously stronger than PAAAM/PEG,which proves that RHTC can reduce the effect of PAAAM on PEG crystallinity.When the content of PEG in the PAAAM/RHTC/PEG is 88.7 wt%,its photothermal conversion storage efficiency can reach 93.3%.Due to the network structure and hydrophilicity of PAAAM,PAAAM/RHTC/PEG composites can also maintain good shape stability in aqueous environment,which broadens the application range of the materials.3.To improve the thermal conductivity of composites,RHTC-BN was prepared with BN as the thermal conductivity filler.The PAAAM/（RHTC-BN）/PEG,PAAAM/RHTC/PEG,and PAAAM/BN/PEG were prepared by the strategy of simultaneous PAAAM synthesis and encapsulation process.Due to the chemical inertness and hydrophobicity of BN,it is difficult to disperse BN in PAAAM/BN/PEG with PAAAM and PEG,so its thermal conductivity is limited.With the help of RHTC,the thermal conductivity of PAAAM/（RHTC-BN）/PEG is 1.2 W/m·K,which is 376%higher than PEG.The temperature of RHTC-BN is as high as 75.3℃ while that of BN is as low as 47.7℃ under the simulated solar radiation.This indicates that RHTC has a good light absorption capacity,and the photothermal conversion and storage efficiency of PAAAM/（RHTC-BN）/PEG can reach 92.6%.4.To solve the strong rigidity of PEG,MF5/（RHTC-BN）with 3D thermally conductive network and MF5/（RHTC-BN）/PEG were successfully prepared using MF as the flexible supporting material.The latent heat capacity,photothermal conversion storage efficiency,and thermal conductivity of MF5/（RHTC-BN）/PEG are 140 J/g,0.9W/m·K,and 92%,respectively.Under thermal stimulation,the MF5/（RHTC-BN）/PEG composites were triggered by the phase transition of PEG,showing excellent shape memory performance and good self-adhesion ability.5.To improve the elastic modulus of flexible composites,PVDF/（RHTC-BN）/PEG flexible composite films were prepared by using PVDF as the supporting material.RHTC in the PVDF/（RHTC-BN）/PEG acts as a key bridge to facilitate the dispersion of BN in PVDF,forming a"sandwich"thermal conductivity structure.Therefore,the PVDF/（RHTC-BN）/PEG composite film has both stress of 2.4 MPa and latent heat capacity of 114.9 J/g.When 5 wt%of RHTC-BN was added,the thermal conductivity and photothermal conversion storage efficiency of PVDF/（RHTC-BN）/PEG are 1.0W/m·K and 92.1%,respectively.