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.