Sustainable Bifunctional Wood Coatings: Biomass Additives Enabling Synergistic Flame Retardancy and UV Shielding

The development of efficient, environmentally friendly, and cost-effective multifunctional wood coatings is crucial for enhancing the sustainable utilization of wood resources. Herein, we report a water-based dual-functional coating (PUL) that integrates phytic acid, urea, and sodium lignosulfonate into a polyaspartic ester (PAE) resin matrix via a two-step brush-coating strategy, enabling concurrent flame retardancy and UV resistance. Micro-scale combustion calorimetry revealed that, compared to conventional PAE coatings, the PUL coating reduced the peak heat release rate by 13.47%, increased the char residue by 70.38%, and significantly lowered the emission of toxic gases. Notably, all coated wood samples exhibited self-extinguishing behavior within 10 s under direct butane flame exposure. Further analysis of pyrolysis gas-phase products and post-combustion condensed-phase structures confirmed the synergistic flame-retardant mechanism between phytic acid-urea and sodium lignosulfonate. Additionally, thanks to the aromatic ring structure and the UV-absorbing chromophores and auxochromes in lignosulfonate, the PUL-coated wood demonstrated excellent UV resistance after 336 h of accelerated UV aging, effectively suppressing color change on the wood surface and maintaining structural stability. This study presents a biomass-based flame-retardant and UV-resistant dual-functional wood coating system, providing a novel strategy for the development of environmentally friendly protective coatings for wood applications.