Construction of biomass-based flame-retardant, antimicrobial and hydrophobic wood coatings with POSS organic–inorganic nanoparticles

The present study utilizes chitosan (CS) and phytic acid (PA) as natural polyelectrolytes, while incorporating Polyhedral Oligomeric Silsesquioxane (POSS), an organic–inorganic hybrid Si-O-Si cage structure, to create a flame retardant, antimicrobial, and hydrophobic coating for wood materials using the layer-by-layer self-assembly method. The POSS flame retardant bisDOPO-NH2-POSS was synthesized by combining 9,10-dihydro-9-oxa-10-phosphaphenathrene (DOPO) with octaminopropyl silsesquioxane (OA-POSS). Subsequently, AgNPs were incorporated into the cage structure of bisDOPO-NH2-POSS through in-situ reduction to fabricate Ag@bisDOPO-NH2-POSS for enhanced antimicrobial efficacy. The CS/PA coating was deposited using the LBL method, which resulted in the formation of a dense char layer during combustion due to both the presence of an inorganic Si-O-Si physical barrier and the synergistic effect of P-N-Si. As a result, self-extinguishing behavior was observed during vertical burning tests, and there was an increase in the limiting oxygen index value to 30.9%. Moreover, by incorporating chitosan, Ag@bisDOPO-NH2-POSS exhibited inhibitory effects against mold such as Aspergillus niger and Lasiodiplodia. The heat release rate (HRR) was reduced by 42.3%, while the total heat release (THR) decreased by 44.4%. The modified wood demonstrates exceptional water repellency, characterized by a static contact angle exceeding 90°. Additionally, the multifunctional coating shows remarkable resilience as it withstands 100 abrasion cycles without compromising its hydrophobic properties. This study presents a sustainable approach to developing a bio-based coating for wood materials that is flame retardant, hydrophobic, and antimicrobial, thereby expanding the potential applications of wood in construction and furniture.