Preparation And Properties Of Phase Change Composites Based On Paraffin@polymethyl Methacrylate

With the growth of world economy and high speed development of industry,the uneven between the growing energy consumption and unrecoverable fossil energy become more and more pressing to be solved.Phase change materials(PCMs)is a new kind of materials for energy storage,which can reversibly store/release a large quantity of latent heat from the surrounding environment near isothermally.The capacity and reliability of the energy system was effectively improved by using of PCMs,which gets the upper hand in improving energy efficiency and developing renewable energy.However,PCMs suffer from some critical defects,such as low thermal conductivity and liquid leakage,which greatly restrict its utilization in many scenarios.In order to overcome the defects of PCMs,microencapsulation of PCMs have been come up with to address these problems.In this thesis,two kinds of phase change microcapsules with different wall materials were designed and prepared based on the free radical polymerization reaction of vinyl monomer and the interfacial hydrolysis-condensation reaction of silane precursors.And compounded with polymer matrix to prepare phase change composites,which broadened their application scope.The main contents of this thesis are as follows:(1)Paraffin wax(Pn)was selected as the core material,Pn@PMMA phase change microcapsules were prepared by the free radical polymerization reaction of methyl methacrylate(MMA).The influence of preparation conditions including the type of emulsifier,cross-linker content and ratio of core to wall on the structure and properties of Pn@PMMA were investigated.The results showed that the Pn@PMMA possessed the high enthalpy and the impermeability is excellent when SMA was used as the emulsifier;the microcapsules have more complete spherical structure and lower leakage rate with the addition of cross-linking agent;and the phase change enthalpy and leakage rate of microcapsules are gradually decreasing with the decrease of core-to-shell ratio,but the thermal conductivity is gradually increasing.Considering all the properties of Pn@PMMA,SMA was used as the emulsifier,the crosslinker addition was 30%,and the core-shell ratio was 1:1 as the best process parameters for the synthesis of Pn@PMMA.The prepared Pn@PMMA has an enthalpy of183.2 J/g and a leakage rate of 4.72%.(2)In order to reduce the leakage rate of the microcapsules and enhance thermal conductivity,a kind of double-layered phase change microcapsules Pn@PMMA@Si O₂ with low leakage rate were fabricated by interfacial polycondensation and radical polymerization.The influence of PMMA content on the structure and properties of Pn@PMMA@Si O₂ was investigated.The results showed that the enthalpy of melting and enthalpy of crystallization of Pn@PMMA@Si O₂ slightly decreased after the introduction of PMMA layer,but still had good phase change thermal storage capacity.Meanwhile,the construction of PMMA layer can effectively reduce the leakage rate of Pn@PMMA@Si O₂ and improve the impermeability of microcapsules.(3)In order to improve the application scope of phase change microcapsules,a series of HDPE/Pn@PMMA@Si O₂ phase change composites(PCCs)were constructed by laminating different fillings of Pn@PMMA@Si O₂ with high density polyethylene(HDPE).We investigated the effect of content on the structure and properties of PCCs.It was shown that the microcapsules were uniformly dispersed in the HDPE matrix,and HPDE was able to support the composites and provide protection to the phase change materials and reduce the leakage rate of the composites.The enthalpy of PCCs-40 is 52.7 J/g and the tensile strength19.96 MPa with 40 wt%microcapsules,at which point the composite has relatively good overall properties.It has potential applications in thermal management and temperature regulation.