Preparation Of Paraffin Microencapsuled Phase Change Materials And Study On Mechanical And Thermal Properties Of Composite Phase Change Gypsum Materials

Phase change materials?PCMs?have great development space in the field of building energy conservation due to their excellent latent heat storage performance.The combination of PCMs with building materials can improve the heat storage performance of buildings without increasing the building's own weight,and achieve the effect of reducing indoor temperature fluctuations and improving thermal comfort of indoor environment.In practical applications,the direct combination of PCMs and building materials will cause leakage of PCMs during thermal cycling,which adversely affects the mechanical properties and durability of building materials.PCMs have a negative impact on the mechanical properties and durability of building materials due to leakage during thermal cycling.The microencapsulation of PCMs provides an effective solution to this problem.In this paper,a kind of phase change paraffin with suitable phase change temperature and low cost was used as the core material.Microencapsuled phase change materials?Micro-PCMs?with melamine-urea-formaldehyde resin and silica as shell materialofthe were prepared by different preparation methods and the thermal properties of Micro-PCMs were analyzed.In order to explore the problems of Micro-PCMs in building materials,the prepared Micro-PCMs were mixed into gypsum matrix to prepare phase change gypsum building materials,the mechanical properties and thermal properties of phase change gypsum building materials were studied.The main research contents and results are as follows:Micro-PCMs with melamine-urea-formaldehyde?MUF?shell materialofthe was prepared by in-situ polymerization method.The effects of different emulsifiers on the particle size distribution,microstructure and latent heat of phase change of microcapsules were studied.The results show that the core paraffin was effectively encapsulated by MUF shell and there was no chemical reaction between them.the"core-shell"structure of the Micro-PCMs was formed.The prepared Micro-PCMs are basically spherical with compact and smooth surface.The addition of graphene oxide?GO?can effectively enhance the thermal stability of Micro-PCMs.When GO,Span80 and Tween80 were used as emulsifier,the particle distribution of Micro-PCMs was relatively concentrated,the melting enthalpy and the crystallization enthalpy were 32.2 J/g and 39.5 J/g,respectively,the encapsulation ratio of paraffin is 49.9%,the thermal decomposition temperature of the core material in the Micro-PCMs is significantly improved,the prepared Micro-PCMs has an excellent impermeability;when GO was used as emulsifier,the melting enthalpy and crystalline enthalpy of the prepared Micro-PCMs are 45.5 J/g and 35.6 J/g,respectively,and whihc has the highest encapsulaiton ratio of 56.4%.Micro-PCMs with SiO₂ as shell and paraffin as the core were successfully prepared by sol-gel method.The effects of different emulsifier and pH conditions on the thermal properties of Micro-PCMs were studied.The results showed that there is no chemical reaction between core and shell materials,and paraffin was successfully encapsulated into the SiO₂ shell.When Span80 and Tween80 were used as emulsifier and under the condition of pH=2.5,the microencapsules prepared that has a dense and smooth suface that has anexcellent;impermeability was good;the particle size of the Micro-PCMs is more uniform;the Micro-PCMs prepared has a high phase change latent and encapsulation ratio,the melting enthalpy and the crystallization enthalpy were 61.12 J/g and 59.52 J/g,respectively,the encapsulation ratio of the Micro-PCMs reached 83.9%.SiO₂ shell played a protective role on PCMs and the thermal decomposition process of the PCMs was slowed down.Compared with pure paraffin,the decomposition temperature of paraffin inside the microencapsules was significant improved,the thermal stability of the PCMs are enhanced.The prepared Micro-PCMs was added to the gypsum matrix to obtain phase change gypsum building materials.The study showed that the mechanical properties of the gypsum building materials gradually decreased with the increase of the microcapsule content.The compatibility of SiO₂ shell microcapsules with gypsum was obviously better than that of MUF shell microcapsules.When the content of SiO₂ shell microcapsules was less than 50 wt%,SiO₂ shell microcapsules were uniformly dispersed among the gypsum matrix;The combination of Micro-PCMs and gypsum building material significantly improved the latent heat of phase change of gypsum building materials and effectively reduced temperature fluctuation during heating and cooling process;phase change gypsum building materials had better thermal stability which can maintained good performance during the long-term cycle process.With the content of Micro-PCMs increasing,the thermal conductivity of phase change gypsum building materials gradually decreased.