Study On Preparation And Thermal Properties Of Microencapsulated Phase Change Material

Microencapsulated phase change material is a shape-stabilized phase change material which is obtained by packaging technology of microcapsules. Storage or release of energy is operated with melting or solidification process of phase change material encapsulated. It always appears as solid appearance because of the solid wall material. As an energy-saving materials, microencapsulated phase change material has a large latent heats, approximate isothermal to the phase transition, no corrosion, no pollution and has been widely used in the fields of solar storage, energy saving building materials, smart thermostat fiber, heat-flow and aerospace .Microencapsulated phase change material was prepared by situ polymerization with butyl stearate as phase change material, melamine-formaldehyde resin as wall material. Different emulsifier types and prepolymer dropping rate on impact of microcapsules morphology were investigated in experiments. The results show that the optimal preparation conditions are the mass ratio of composite emulsifier TA to span-80 5∶1, dropping rate of prepolymer 0.8ml/min-1.2ml/min. By controlling these conditions, microcapsules are prepared with good morphology and tough shell material. Thermal storage capacity of microcapsules was investigated. DSC analysis indicated that the butyl stearate in the microcapsules melts at 25.80℃and crystallizes at 25.61℃. It has latent heats of 86.05J/g and 54.16J/g for melting and crystallization, respectively. After 100 times phase change cycle microcapsules have good form and durability.Another kind of microcapsules was prepared by emulsion Polymerization with butyl stearate as phase change material, methyl methacrylate as the monomer, allyl methacrylate as crosslinking agent. Different catalyst type, polymerization temperature, emulsifier speed and emulsifier type on the impact of microcapsules were researched in experiment. The results show that the optimal preparation conditions are polymerization temperature 75℃, mulsifier speed and emulsification time 3000rpm and 15min respectively, choice of emulsifier with a combination of TA,polyvinyl alcohol and sodium polyacrylate. It shows good spherical microcapsules and slight adhesion of the microcapsules prepared with Tert-butyl peroxide and azobisisobutyronitrile used as catalyst respectively. Heat storage capacity of microencapsulated phase change materials was determined. DSC analysis indicates that the butyl stearate in the microcapsules melts at 23.66℃and crystallizes at 24.87℃. It has latent heats of 93.37J/g and 94.53J/g for melting and crystallization, respectively.Another kind of microencapsulated phase change materials was prepared by phase separation with tetradecane as phase change material, methyl methacrylate and styrene copolymer as wall material. Emulsifier type, the ratio of phase change material and wall material and the different emulsifying machine speed and time on the impact of microcapsules were studied in experiments. The results show that the optimal preparation conditions are with emulsifier a combination of TA and polyvinyl alcohol, the emulsifier speed 3000rpm. As the core material taking 44.4% of the mass fraction, good spherical microcapsules are prepared without outside shell sag. DSC analysis indicates that the tetradecane in the microcapsules melts at 2.49℃. It has latent heats of 93.37J/g and 72.72J/g for melting and crystallization, respectively.