Preparation And Properties Of Polyurethane-based Solid-solid Phase Change Materials

Phase change materials(PCMs)for energy storage could store and release latent heat through repeated phase transition,which are widely used in buildings,aerospace and defense,solar energy devices,biomedicine,electronic equipment and smart textiles.However,there is always leakage problem when traditional PCMs including polyethylene glycol(PEG)melt,which hinders their actual applications.Besides,commonly used organic PCMs have poor light absorbance and electrical conductivity,resulting in lower energy conversion and storage efficiency.Therefore,to design and fabricate solid-solid phase change materials(SSPCMs)with high latent heat,excellent light-/electro-thermal conversion and storage shows a certain of theoretical guidance and practical application value.In this paper,works aiming at resolving the aboved scientific issues including leakage problem and functionalization of PEG were carried out.Nano particles/polyurethane(PU)-based solid-solid SSPCMs(PUSSPCMs)have been fabiricated with high latent heat,excellent thermal stability and reliability and light-/electro-thermal conversion and storage.1.A series of PUSSPCMs with different amount of PEG and hexamethylene diisocyanate biuret(HDIB)were synthesized through one-step.The phase change temperature and enthalpy were tuned through the ratio of PEG and HDIB.Based on this,the influence of halloysite nanotubes(HNTs)on the phase change properties of the system was investigated.Results show that HNTs could not only work synergistically with HDIB to endow the system with form-stability,but also provide numerous nucleation sites for PEG segments,which improves the crystallization temperature and the latent heat.Moreover,the thermal stability is elevated substantially for the thermal barrier of HNTs.2.Graphene oxide(GO)was incorporated into the system through in-situ reaction and the effects of it on the performance of the system were studied.GO dispersed homogeneously into PUSSPCMs as crosslinking agent and enhanced the mechanical strength greatly.However,the abandunt oxygen-containing groups on GO,which works as heteregeneous nucleation agent,affect the degree of confinements of PEG segments,resulting in the elevation of crystallization temperature but no variation of phase change latent heat.3.To obtain PUSSPCMs with light-thermal conversion and storage,GO was reduced through simple solvothermal treatment of N,N-Dimethylformamide(DMF)solution mixed with GO sheets,PEG and HDIB.The influence of GO size on the phase change performance of the system was investigated.Results show that reduced GO(RGO)sheets could not only work as crosslinking agent to endow the system with remarkable solid-solid phase change performance,but also hinder the interaction of PU chians tied to the both sides of the sheets.Besides,the crystallization properties have been improved for the heterogeneous nucleation effect and the obstacle of interactions among PU chains.What’s more,the thermal stability has been improved a lot.Besides,the crystallization performance is GO size-dependent.The smaller the size is,the higher the latent heat is.4.To achieve the electro-thermal conversion and storage,HNTs hybrid graphene aerogel(HNTs-GA)was fabricated through facile reduction and freezing.Then the composite of HNTs-GA/PUSSPCMs was prepared by vacuum impregnation.HNTs loaded randomly on the surface of wall cell of GA,could not only prevent the graphene sheets from restacking and enhance the degree of reduction correspondingly,but also could strengthen the skeleton of GA,which enables the air-drying easily without volume shrinkage.FT-IR study indicates that when impregnated into HNTs-GA,the hydrogen bonding of the system is weakened to some extent.Hence,the free movement of PEG segments could be improved.What’s more,HNTs could serve as heteregeneous nucleation agent,which would improve the crystallization of PEG segments.The light-/electro-thermal energy conversion and storage efficiency is 78.4%and 66.3%,respectively,with only 1.02 wt%GA owing to the excellent light absorption and electrical conductivity.Due to the existence of three dimensional cellular structure,which could work as efficient thermal barrier,the thermal stability of the system gets a lot improvement.5.The ternary composite of GA/ZnO/PUSSPCMs was prepared through impregnating the DMF mixture of nano zinc oxide(ZnO),PEG and HDIB into GA under vucuum to give full play of heterogeneous nucleation effect of nano particles.ZnO serve as light absorber synergistically with GA.The electro-thermal and light-thermal energy conversion and storage of the system are 84.4%and 80.1%,respectively,when incorporating 0.97 wt%ZnO and 1.32 wt%GA.