Preparation And Characterization Of Microencapsulated Phase Change Materials With Dual Function Of Thermal Energy Storage And UV-shielding

Phase change materials?PCMs?have become a research topic worldwide in virtue of high latent heat and narrow temperature range during phase transition process.PCMs are used for the efficient utilization of renewable and clean energy resources to achieve the sustainable development.Microencapsulated PCMs?MPCMs?have been recognized as potential materials for heat energy storage in the fields of building,textile fabrics and medical treatment.However,the further research shows that the problems of sole function,poor mechanical properties,low thermal conductivity and bad thermal response exist in MPCMs with the organic shell.In this paper,a kind of bifunctional MPCMs was designed and fabricated by doping the inorganic functional particles of rutile titanium dioxide?TiO₂?nanoparticles as the ultraviolet absorber into the organic shell matrix.Surface modification of TiO₂ was carried out first to improve its degree of dispersion at the poly?methyl-methacrylate??PMMA?matrix,avoid agglomerating and overcome the organic-inorganic interface problem using?-methacryloxypropyltrimethoxysilane?MPTMS?silane coupling agent.The three silicon functional groups of MPTMS can react with the hydroxyl groups on the surface of TiO₂ and the silicon functional groups of itself to form a film on the surface of TiO₂.Moreover,the carbon functional group of MPTMS can bond with the functional group on the polymer chain to form the semi-interpenetrating or interpenetrating layer at the organic-inorganic interface.Thus,the excellent performance of the composite can be achieved.Microcapsules?MPCMs/TiO₂?with thermal energy storage and UV-shielding functions were successfully prepared by the method of suspension polymerization.The O/W reaction system consists of n-octadecane and methyl methacrylate?MMA?as oil phase,deionized water as water phase and the sodium salt of styrene-maleitc anhydride copolymer?TA?as emulsifier.During the process of cross-linking polymerization,the polymer precipitates from the oil phase and moves to the surface of the oil droplets to form the microcapsules and TiO₂ nanoparticles are well fixed in the cross-linked network structure of the polymer.The results showed that the as-prepared microcapsules are spherical and about 10-20?m in average diameter.With the increasing addition amount of TiO₂ nanoparticles,the microcapsules result in more regular spherical shape.This may suggest that the addition of TiO₂ nanoparticles could enhance the mechanical strength of the shell material to resist internal and external stress.The results of differential scanning calorimeter?DSC?and thermogravimetric analyzer?TGA?demonstrated that the microcapsules exhibited high thermal storage capability,good thermal reliability and stability.The latent heat of almost microcapsules is higher than 100kJ·kg^-1.The T_oc?crystallization onset temperature?moves to the high temperature and the exothermic peaks become narrower with the increasing of TiO₂ nanoparticles.We can deduce that the addition of TiO₂ nanoparticles promotes the crystallization process of the microencapsulated n-octadecane.Ultraviolet visible spectrophotometer?UV-vis?measurements showed that the MPCMs/TiO₂ had good UV-shielding property.The resultant samples of MPCMs/TiO₂ with thermal energy storage and UV-shielding functions may become the potential materials in the advanced applications of intelligent textile and buildings.