Bio-Based Dual-Functionalized Phase Change Composite: Ultrafast Solar-to-Thermal Conversion and Reinforced Heat Storage Capacity

Rice husk (RH) is a highly recyclable biomass and often used as biofuel. However, residual rice husk ash (RHA) from burning RH is difficult to dispose and causes a serious environment threat. In this study, high-value utility of RHA in terms of form-stable phase change materials (PCMs) was pointed out. RHA was introduced as a supporting material to encapsulate paraffin (PA) to solve the leakage of PA. In order to enhance heat storage capacity, the two-step method was proposed via a neutralization reaction and chemically hydrophobic grafting process to construct a unique RHA nanoporous structure with high adsorptivity of PA. The influence and mechanism of the surface structure and chemical properties of an RHA support on hydrophobicity were deeply discussed, in which the surface chemical structures and fractal characteristics were revealed. The results indicated that PA/bio-based RHA composites possessed enhanced enthalpies due to the synergism of pore structure enlargement and surface hydrophobization of the RHA support. Furthermore, the composite PCM showed excellent solar-to-thermal conversion and thermal cycling reliability. This work provides a new insight into the high value utilization of biomass waste RHA and the development of high performance and multifunction for PA/bio-based RHA phase change composites.