Enhanced thermal properties of hydrate salt/poly (acrylate sodium) copolymer hydrogel as form-stable phase change material via incorporation of hydroxyl carbon nanotubes

The collecting energy from solar radiation using phase change materials is significant in the field of thermal storage. In the current work, a novel MWCNT-modified hydrate salt/poly (acrylate sodium) copolymer hydrogel (MWCNT-GS/PAAS) form-stable composite PCM was well prepared using mechanical mixing method. The form-stable ability, microstructure, heat storage capacity, thermal stability and thermal-cycling reliability of the prepared MWCNT-GS/PAAS were investigated. The leakage experiment exhibited that the MWCNT-GS/PAAS containing 7 wt% PAAS can maintain original gel-structure without leakage in melting state of hydrate salt. Moreover, scanning electron microscopy was used to demonstrate that the hydrate salt PCM was coated with densified hydrogel film. ATR-FTIR and Raman spectra results indicated that the hydrate salt PCM was encapsulated successfully within the network gel-structure. Differential scanning calorimetry (DSC) suggested that the MWCNT-GS/PAAS composite possessed good thermal storage capacity, of which the latent heat reached up to 187.2 J/g. Thermal gravimetric analysis (TGA) indicated that the retention ratio of the crystal water in MWCNT-GS/PAAS is as high as 64.8 wt% at the temperature where the Glauber's salt completely dehydrated. The heat transfer performance suggested that the thermal conductivity and thermal diffusivity of the MWCNT-GS/PAAS composite increased by 141.7% and 167.1% compared with those of the pure GS. Furthermore, being subjected to 500 thermal cycles, the prepared composite maintained favorable thermal and chemical stability. The obtained results indicated MWCNT-GS/PAAS composite was an outstanding candidate used for solar energy storage systems.