Functional wood-based reversible thermochromic composite phase change energy storage materials for visual information storage and flame retardant

Flame-retardant thermochromic composite phase change materials (CPCMs) that offer visual temperature monitoring and energy storage capabilities are essential for applications in smart buildings. Encapsulation of phase change materials (PCMs) in three-dimensional continuous porous carriers is an effective strategy to ensure shape stability in conventional latent heat storage systems. Wood, a renewable resource with a natural porous structure, is delignified to create a more complex three-dimensional hierarchical porous framework. Thermochromic materials and nano‑calcium carbonate (nanoCaCO 3 ) are then melt-blended and impregnated into the delignified wood through vacuum impregnation. The resulting composite phase change material, CTBC/DW, possesses high heat storage density, reversible thermochromic properties, information storage and concealment capabilities, and flame retardancy. Differential scanning calorimetry (DSC) results show that CTBC/DW achieves a high thermal energy storage density (142.70–171.40 J g −1 at 7–14 wt% nanoCaCO₃ loading) and excellent thermal stability. Importantly, CTBC/DW demonstrates significant reversible thermochromic behavior, with color changes from dark blue (25 °C) to Off-white (40 °C), making it useful for visualizing the phase change thermal storage process and enabling information access. Additionally, nanoCaCO 3 was introduced as a cladding material to solve the defect of flammability of wood, thereby improving the service life of the composites. This composite material holds considerable potential for a range of thermal energy storage applications, including information storage, decoration, furniture, and energy-efficient building solutions.