A novel biochar supported dual-flame-retardant composite phase change material (PCM) for building energy saving

The incorporation of phase change materials (PCM) can enhance the thermal performance of building envelopes and improve indoor thermal comfort. However, challenges such as high costs and flammability issues have hindered their widespread application. In this study, agricultural waste (rice husk) was utilized to develop an environmentally friendly biochar-based supporting matrix (rice husk carbon, RHC) for the adsorption of n-octadecane. Ammonium polyphosphate (APP), epoxy resin (EP), and expanded graphite (EG) were utilized in the development of a flame-retardant and conductivity-enhanced composite phase change material (PCM). The thermophysical and flame retardant properties are investigated at both macro and micro levels. The results show that the proposed composite PCM (n-octadecane/RHC/EG/APP/EP) containing 15 wt% APP exhibits excellent flame-retardant performance, achieving the UL-94 V-0 level. Additionally, the Limiting Oxygen Index (LOI) has increased from 18.3 % to 23.7 %, while the Total Heat Release (THR), as measured by cone calorimeter, has experienced a reduction of 20 %. DSC analysis revealed that the as-prepared CPCM exhibited melting peak temperatures of 27.0 °C and a latent heat of fusion of 128 J/g. Additionally, the material demonstrated excellent shape stability after 300 thermal cycles, with a minimal degree of supercooling and excellent leak proofness. This study presents a viable method for fabricating biochar-based CPCM that exhibits excellent flame retardancy, shape stability, and high phase change efficiency, demonstrating significant potential for application in building energy conservation. • A novel biochar supported flame-retardant composite phase change material (PCM) was synthesized. • The composite PCM (CPCM) demonstrate superior thermal storage capabilities and exceptional fire resistance properties. • The synergistic flame-retardant mechanism of the CPCM was revealed.