A novel bio-based multifunctional coating material for wood protection: Enhancing flame retardancy, hydrophobicity and durability

Natural wood is a sustainable carbon-neutral building material, while its inherent high flammability, strong hydrophilicity, and poor weather resistance severely limit its long-term outdoor application. In this study, a multifunctional coating for high-efficiency wood protection was developed using bio-based material. Natural rubber-modified tung oil (TOR) was synthesized via Diels-Alder cycloaddition reaction as the film-forming matrix, agricultural waste-derived straw biochar was used as the bio-based flame-retardant filler, and a PDMS/nano-silica topcoat was constructed to achieve integrated hydrophobic and flame-retardant protection. The comprehensive performance of the coated wood was systematically characterized, and its full-scale fire protection effect was verified via FDS numerical simulation. The results show that the TOR-BC coating gives wood a static water contact angle of 127.8°, and raises its 600 °C char residue yield from 15.2% to 28.6%. The wood after coating reaches a LOI of 33.0%. Compared with pure wood, the coated sample shows a 45.6% decrease in peak heat release rate, a 42.0% decrease in total heat release rate, and a 72.6% decrease in total smoke production, which achieves excellent efficient synergistic flame retardant and smoke suppression performance. The coating maintains over 95% hydrophobic retention after 90 days of natural outdoor aging, and full-scale fire simulation confirms that it can effectively inhibit building fire spread and extend the personnel evacuation time by 25% - 30%. This green, bio-based coating provides a low-cost and high-performance solution for long-term outdoor wood protection, with broad application prospects in wood structure engineering and architectural heritage conservation.