Robust interfacial assembly of wood-based composites for high-efficiency cooling and fire safety

The development of sustainable building envelopes capable of passive daytime radiative cooling (PDRC) is critical for reducing global cooling energy consumption. However, the application of wood-based PDRC materials in construction is severely restricted by their intrinsic flammability and moisture sensitivity. To address these engineering challenges, this study develops a multifunctional delignified wood composite (DW-PCKTi-PVDF) designed for high-efficiency thermal management and superior durability. Through a vacuum-assisted impregnation process, a robust skeleton was constructed using phosphorylated cellulose (PC), kaolin, and titanium dioxide (TiO₂), followed by a surface modification with polyvinylidene fluoride (PVDF). The resulting composite exhibits exceptional optical properties with a solar reflectance of 88.3% and an atmospheric window emissivity of 96.4%, achieving a temperature reduction of 9.6 °C relative to natural wood under direct sunlight. Crucially for building safety, the synergistic interaction between PC and kaolin significantly enhances flame retardancy, increasing the char yield at 800 °C to 34.6% and reducing the peak heat release rate by 18.6% compared to natural wood. Mechanism analysis reveals that PC accelerates catalytic dehydration and carbonization, forming a dense barrier that suppresses combustion. Furthermore, the composite demonstrates excellent weather resistance with a superhydrophobic surface (water contact angle of 134°) and improved tensile strength (8.6 MPa), ensuring structural integrity in humid environments. Whole-building energy simulations across diverse climatic zones predict cooling energy savings of 6%–12%. These findings demonstrate that the DW-PCKTi-PVDF composite is a promising, safe, and energy-efficient material for sustainable construction applications.