Phase change material microcapsules with melamine resin shell via cellulose nanocrystal stabilized Pickering emulsion in-situ polymerization

Thermal energy storage technology based on phase change materials (PCMs) is promising for temperature regulation and thermal energy storage. However, the applications of organic PCMs are hindered from their leakage issue. Encapsulating PCMs in microcapsules with polymer shell could effectively prevent the leakage of PCMs and enhance heat conduction. Herein, PCM microcapsules with melamine–formaldehyde resin (MF) as shell were prepared via cellulose nanocrystal (CNC) stabilized Pickering emulsion in-situ polymerization. CNCs were chosen as emulsifiers of Pickering emulsion and reinforcing nanofillers of MF shell due to their outstanding emulsifying ability, mechanical strength, and sustainability. Paraffin wax (PW) and n-octadecane (C18) were employed as PCMs, respectively. The prepared PCM microcapsules are in diameter of 4 μm with a tunable thickness of MF shell. The phase change enthalpy of PW and C18 microcapsules are as high as 164.8 and 185.1 J/g, corresponding to PCM core material content of 87.0 and 84.3%, respectively. PCM microcapsules are stable below 200 ℃ and display a retention rate of the phase change enthalpy reach up to 99.7% after 200 cycles of heating–cooling. Moreover, the PCM microcapsules are self-extinguishing due to the flame-retardant properties of MF shell. The promising applications of PCM microcapsules in the field of temperature regulation were also demonstrated.