Sustainable super-light and high-strength wood-based composite foam with hydrophobic, flame-retardant and thermal-insulating properties

This study introduces an innovative methodology for the development of sustainable, high-performance building insulation materials via molecular engineering of Cellulose nanofibers/Polybenzoxazine-Polyvinyl alcohol (CNFs/PBZ-PVA) composite foams modified with environmentally friendly protonated Poly(ethyleneimine)-Phytic acid (PEI (H⁺)-PA) ligand. The use of renewable bio-based components and eco-friendly modification processes underscores the material's alignment with circular economy principles. The optimized formulation, characterized by a 2: 1 CNFs/PEI (H⁺)-PA ratio, exhibits exceptional multifunctional properties, including a uniform microporous structure (15–35 μm), remarkable compressive strength (2.77 MPa at 80 % strain), and superior thermal insulation performance (0.0504 W/(m·K)). In addition, the integrated P-N synergistic system substantially enhances flame-retardancy (LOI=37.2 %, UL-94 V-0 rating), achieving reductions in heat release and smoke production by 41.67–81.43 %. Subsequent silane modification further elevates hydrophobicity (contact angle of 114.5°) and fire safety (LOI=39.1 %, 82.74 % reduction in PHRR). The fabricated wood-based insulation panel demonstrates outstanding thermal resistance (surface temperature of 52.8 °C after exposure to 120 °C for 180 s), surpassing the performance of conventional commercial products. This research offers a green materials solution that effectively integrates thermal management, mechanical durability, and fire safety for sustainable building applications.