| Organic phase change materials have shortcomings such as phase separation after melting,flow after melting,and low thermal conductivity.The above shortcomings will cause phase change materials to have problems of failure and low use efficiency.The above problems can be solved by restricting the flow of phase change materials(form stable)and thermal enhancement.However,the existing modifying methods will greatly reduce the heat storage density of the material.In this research,a new method of shaping and thermal conductivity modification that has less effect on the heat storage density of the material,and to provide beneficial experience for solving the above problems.Polyethylene glycol(PEG)was modified by polycarboxylation to prepare polyethylene glycol gel-shaped phase change material,and the shape-shaped phase change material was thermally modified.The specific research plan is as follows:Polycarboxylate modification of polyethylene glycol with trimellitic anhydride and pyromellitic anhydride;The following two routes are used to prepare stereotyped phase change materials: epoxy resin is used to directly cross polycarboxyl polyethylene glycol.Joint curing is used to prepare a shaped phase change material,and polycarboxyl polyethylene glycol and epoxy resin are dissolved in a polyethylene glycol melt and then cross-linked and solidified to prepare a polyethylene glycol gel type shaped phase change material.The in-situ dispersion process is used to add thermally conductive fillers such as expanded graphite and carboxylated multi-walled carbon nanotubes to the shaped phase change material to improve the thermal conductivity of the shaped phase change material.Fourier transform infrared spectroscopy and hydrogen nuclear magnetic resonance spectroscopy were used to characterize the structure of polycarboxypolyethylene glycol,and the degree of reaction was studied by titration.The thermal stability and heat storage and release capacity of the prepared shaped phase change materials were characterized.The thermal conductivity of shaped phase change materials was studied.The rules of the original dispersion process and the shape of the thermally conductive filler and then to the change of the thermal conductivity of the material were sorted out.The main findings are as follows:Using trimellitic anhydride and pyromellitic anhydride to polycarboxylate polyethylene glycol,the optimal reaction time of this reaction is 8 hours,and the reaction degrees at this time are 85.72% and 86.63% respectively;the number average molecular weights of the products are respectively 10022 and 4395,the weight average molecular weight is 21827 and 5821,respectively.Polycarboxyl polyethylene glycol and ethylene glycol diglycidyl ether are dissolved in polyethylene glycol and then solidified.The melting of the series samples was 157.04J/g and the crystalline radon was 137.20J/g,respectively,which was 102%and 85% higher than the samples that were not dissolved and polyethyl glycol,and the heat storage density reached 86.80%(in PEG4000)and 84.76%(in PEG20000).With the increase of polyethyl glycol content,the diffraction peak on XRD gradually increases,and the spherical crystal size observed under polarizing microscope gradually becomes larger..The thermal conductivity of the shaped phase change material is improved by adding thermally conductive fillers.For the shaped phase change materials that use expanded graphite to improve the thermal conductivity,the in-situ dispersion process has a negative effect on the thermal conductivity.Compared with the samples without the in-situ dispersion process,the thermal conductivity decreases by 32.54%,38.72%,42.58%,58.84%,61.82%;For shaped phase change materials that use carboxylated multi-walled carbon nanotubes to improve thermal conductivity,the in-situ dispersion process has a positive effect on thermal conductivity: the thermal conductivity of samples is improved compared to samples without in-situ dispersion process Respectively: 5.45%,9.67%,8.57%,12.27% and 29.93%. |
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