Microencapsulated Paraffin Phase-Change Material with Calcium Carbonate Shell for Thermal Energy Storage and Solar-Thermal Conversion

A series of microencapsulated phase-change materials (MEPCMs) based on paraffin core and calcium carbonate (CaCO3) shell were synthesized, and the effect of emulsifier type and pH value on morphology, structure, and properties of paraffin@CaCO3 MEPCMs were investigated. The results showed that CaCO3 shell was formed in vaterite and calcite crystalline phase when emulsifier was sodium dodecyl benzene sulfonate and styrene-maleic anhydride (SMA), respectively. When sodium dodecyl sulfate was used as an emulsifier, both vaterite and calcite CaCO3 were formed. The forming mechanism of emulsifier type on CaCO3 crystalline phase was studied. Furthermore, phase-change enthalpy and leakage rate of MEPCMs were related with the type of emulsifier and the pH value of the emulsion. With optimum condition of SMA as emulsifier and pH value of 7, paraffin@CaCO3 MEPCMs had an encapsulation ratio at 56.6% and leakage rate at 2.88%, illustrating its considerable heat storage capability and leakage-prevention property. The 50 heating-cooling cycles test indicated that the MEPCMs owned excellent thermal reliability. The thermal conductivity of MEPCMs was significantly improved due to the existence of CaCO3 shell. In addition to excellent thermal storage ability, the paraffin@CaCO3 MEPCMs also owned good mechanical property and light-to-heat energy conversion efficiency. The characteristics of MEPCMs indicated its potential application in solar energy resource.