Self-healing and intrinsically flame-retardant vanillin-derived epoxy wood coatings with a Schiff base structure

The development of sustainable and multifunctional coatings is essential for enhancing the safety and service life of wooden materials. In this study, a bio-based epoxy resin (VE) was synthesized from vanillin and epichlorohydrin, followed by curing with amino-functionalized polyhedral oligomeric silsesquioxane (OA-POSS). This process yielded a crosslinked network (VE/OA-POSS) containing dynamic imine bonds. The resulting VE/OA-POSS coating demonstrated outstanding self-healing performance, achieving 100% scratch recovery within 15 minutes at 65 °C. It also exhibited remarkable flame retardancy, with a limiting oxygen index (LOI) of 33.1% and a UL-94 V-0 rating, alongside enhanced mechanical properties reflected by a pencil hardness of 6H. Compared to a petroleum-based epoxy coating (E-51/DDM), cone calorimetry tests revealed significant reductions in both the peak heat release rate (36.0%) and total smoke production (71.2%). The flame-retardant mechanism was attributed to the formation of a condensed-phase, silicon-doped char layer with a more ordered, silicon-doped char layer (I_D/I_G = 1.86), serving as an effective thermal barrier, coupled with the dilution effect of non-combustible gases in the gas phase. This work presents a sustainable and feasible strategy for multifunctional wood protection.