Synthesis of a vanillin‐based curing agent and its application in wood to improve dimensional stability and flame retardancy

Abstract A novel multifunctional phosphorus‐containing curing agent monomer (PPBMBA) was designed and prepared based on vanillin by the nucleophilic substitution reaction and Pinnick oxidation with phenylphosphonic dichloride (PPDCL). Then a series of epoxy resin (EP) impregnated reinforced wood samples were prepared by combining PPBMBA to improve the dimensional stability and flame retardancy of wood. Differential scanning calorimetry results showed that the curing ability of PPBMBA to EP formulations is equivalent to that of industrial amine curing agents, while simultaneously being flame retardant and environmentally friendly. Scanning electron microscopy (SEM) observation found that the cured EP composite was widely distributed in the wood. Besides, the water uptake rate and volumetric swelling (S) of the impregnated wood sample W‐EP‐0.10 were 59.8% and 67.8% lower than that of pure wood respectively, while the anti‐swelling efficiency (ASE) value was as high as 67.7%. The parallel‐to‐grain compression strength (CS) of the W‐EP‐0.10 was increased by up to 78.3% compared to that of pure wood, while the limiting oxygen index increased from 21.7% to 26.8%, and UL 94 reached V‐0 level. TGA‐FTIR and SEM analysis demonstrated that the thermal stability and flame retardancy of the impregnated wood samples were improved by generating non‐flammable gases and forming an insulating char layer synergistically. From a practical standpoint, this work has significant engineering application value for the development of value‐added wood products with high‐efficiency fire safety and dimensional stability from relatively low‐cost wood.