Synthesis, Thermal Properties Of Microencapsulated Phase Change Materials

Microencapsulated phase change material (MCPCMs), a composite using latent heat to storage thermal energy, can solve the energy mismatch between the time and space, supply and demand. And it also can prevent solid-liquid phase separation, leakage of liquid phase, difficulties of storage and transportation and other problems happening when phase change materials using alone. Therefore, four kinds of paraffin wax coated microencapsulated phase change material in different precursors of silicon and chitosan (CS) were prepared, and the chemical structure, thermal properties and thermal stability were tests.Paraffin/SiO2composite phase change material was prepared by Sol-Gel in which paraffin as phase change material, water as solvent, SiO2as carrier and tetraethoxysilane (TEOS) as precursor. Fourier transformation infrared spectrometer (FT-IR), X-ray diffractometer (XRD) and scanning electronic microscope (SEM) were used to determine chemical structure, crystalloid phase and microstructure of microencapsulated paraffin composites with SiO2shell, respectively. The thermal properties and thermal stability were investigated by the differential scanning calorimeter (DSC) and thermo gravimetric analyzer (TG). The results showed that the composites had similar structures and good structural stability in different emulsification process. The maximum microencapsulation ratio of microcapsules was prepared by emulsification and reversed phase emulsification were47.45%and61.88%respectively. The melting latent heats of them were measured as78.73J/g and101.98J/g. The freezing latent heats of them were77.14J/g and101.28J/g. The rate of change of the latent heat after thermal cycles was25.02%,22.31%for Paraffin/SiO2-E and2.81%,3.43%for Paraffin/SiO2-R. The weight loss was changed12.15%and0.05%respectively. In conclusion the inverted emulsion method is more suitable for the preparation of paraffin/SiO2microencapsulated phase change material with good thermal and stability properties.Paraffin/CS microencapsulated phase change material with uniform sizes and smooth surface were prepared by Sodium hydroxide curing sol-gel method. When the core-shell ratio as5:1, emulsifier content as5%, the microcapsules prepared had good heat storage properties with a maximum microencapsulation ratio of79.80%, the latent heat of melting and solidification were103.97J/g and111.24J/g, and the change rate were3.86%and1.49%after subjected to200thermal cycling.Paraffin/CS-SiO2microencapsulated phase change material was prepared by sol-gel method in which paraffin as phase change material, water as solvent, TEOS as precursor and CS-SiO2as carrier. When the content of CTAB emulsifier was1%, the Paraffin/CS-SiO2had better heat storage properties with an amount of62.13%coating, the latent heat of were measured as80.832J/g and86.73J/g. The rate of change for latent heat after200thermal cycles was0.64%and0.05%, respectively.Microencapsulated paraffin with silicon dioxide shell as composite thermal energy storage material was prepared by using self-assembly technique. The results show that the spherical microcapsule was formed, and the silicon dioxide acted as the shell material which prevented the leakage of the melted paraffin. The maximum microencapsulation ratio was50.23%. The melting and freezing temperature of the microcapsule were measured as61.9℃and55.6℃. The melting and freezing latent heats were measured as66.056J/g and69.407J/g. The change rate of latent heat after200thermal cycles was0.64%and0.05%. And the paraffin/SiO2microcapsule has good thermal stability and structural stability.