Preparation,Thermal Properties And Applications In Thermal Management Of Phase Microcapsules Modified By High Thermal Conductivity Fillers

Phase change energy storage materials（PCMs）play a pivotal role in the sustainable utilization of energy.Currently,they have been widely used in the fields of Solar thermal conversion,temperature control of Electronic products,heat dissipation of Batteries,Clothing,Textiles and thermal regulation of Buildings,etc.However,Phase Change Materials have the problems of volume change and liquid leakage pollution in the solid-liquid phase transformation process,and their thermal conductivity is poor.Affect the possibility of wider application.Encapsulation of phase change materials by microcapsules can effectively prevent the volume change and liquid leakage caused by phase change of PCMs,and can improve the thermal conductivity by modifying the high thermal conductivity filler.Based on this,this paper proposes the synthesis of phase change microcapsules with melamine formaldehyde resin（MF）shell wall coated with paraffin wax,and uses boron nitride nano-sheet（BNNSs）and graphene oxide（GO）composite nano-sheet formed by self-assembly as high thermal conductivity filler to conduct thermal conductivity modification of phase change microcapsules.On the basis of not affecting the heat storage and sealing properties of phase change microcapsules,The thermal conductivity of phase change microcapsules was improved and applied to fabrics and epoxy resins to give different materials temperature control properties.（1）GO was prepared by Hummers method,BNNSs modified by Amino group was prepared by ball milling method,and GO and BNNSs were respectively used as modified fillers.Phase change microcapsules modified by single filler were prepared by in-situ polymerization.SEM,AFM,DLS and FTIR showed that both GO and BNNSs were nanosheets of uniform size,and the characteristic peaks of functional groups existed on the surface,indicating that the preparation was successful.The SEM test of the modified phase change microcapsules showed that the microcapsules were complete spherical in morphology,uniform in size,no obvious damage,and there were rough bumps on the surface caused by GO or BNNSs modification,indicating that the modified microcapsules were successfully synthesized.The thermal conductivity test showed that the thermal conductivity of modified phase change microcapsules was improved,and the GO modified microcapsules had a more obvious improvement.DSC test showed that the thermal storage performance of modified microcapsules decreased,and BNNSs modified microcapsules decreased less.（2）BN/GO composite nanosheets were prepared by self-assembly using the synergistic effect of BNNSs and GO.The effects of ultrasonic treatment power,mass ratio of filler,solid content of dispersed liquid and p H of dispersed liquid on the particle size of composite nanosheets were studied,and modified phase change microcapsules were prepared using composite nanosheets.Through SEM test,it is found that the modified microcapsules are spherical,uniform in size and rough convex on the surface.Moreover,the microstructure of the modified microcapsules is characterized by FTIR,Raman and EDX tests,and the results prove that the modified microcapsules are synthesized successfully.Through the leakage rate test,it was found that the leakage rate of modified microcapsules was lower than 0.6%at 70℃,indicating that the modified microcapsules had good sealing performance.The thermal conductivity test showed that the thermal conductivity（TC value）increased by 62.6%compared with that of paraffin,and the thermal conductivity of modified microcapsules was greatly improved.DSC test showed that the phase change enthalpy was up to～200 J·g^-1,the coating rate was more than 92%,and the heat storage performance of the modified microcapsules did not decrease significantly.After 100DSC cycles,it was found that the modified microcapsules had no change in phase transition behavior,indicating that they had good cyclic thermal stability.（3）Modified phase change microcapsules were used to adjust the temperature of the fabric,and the microcapsules were combined with epoxy resin to obtain composite materials.The influence of the type of modified microcapsules and the amount of added on the thermal properties of the composite materials was studied.SEM test showed that modified microcapsules were uniformly distributed on the micro surface and there was no damage phenomenon,indicating the success of temperature adjustment finishing.Through the infrared thermal imaging test of the temperature-regulating finished fabric,it is found that there is a 15-20 s temperature buffer during the temperature-driving process in high temperature environment,indicating that the fabric has a certain temperature control performance.SEM test of epoxy resin composites showed that uniform spherical pits existed in the fracture section,and there was no obvious boundary between matrix and pits,indicating that epoxy resin and modified microcapsules were successfully combined with good compatibility.The thermal conductivity test shows that the thermal conductivity of epoxy resin composites has been improved to some extent.Through the infrared thermal imaging test of epoxy resin composites,it is found that there are obvious temperature plateau regions in different ambient temperatures,and the temperature plateau regions can be controlled within the range of 90-180 s by controlling the addition amount of microcapsules,indicating that epoxy resin composites have controllable temperature regulation performance.In this paper,the phase change microcapsules coated with paraffin core materials were successfully modified by using BNNSs and GO composite nanosheets as high thermal conductivity filler.The thermal conductivity of the phase change microcapsules obtained was significantly improved,and they keep high thermal storage performance,high sealing performance and high cyclic thermal stability.The obtained phase change microcapsules can provide controllable thermal conductivity and temperature control properties for different materials,which proves that the phase change microcapsules can play an important role in many practical temperature control applications.