Facile Synthesis of a Phosphorus-Containing Sustainable Biomolecular Platform from Vanillin for the Production of Mechanically Strong and Highly Flame-Retardant Resins

A novel chemical architecture, vanillin-based phosphorus-containing flame-retardant building block (VP), was successfully synthesized as a sustainable platform biomolecule to be converted into fire-retardant epoxy (VPE) and polyurethane (VPU) resins for application as environmentally friendly adhesives. Structural characterizations confirmed the successful functionalization through their molecular structures. A series of VPU and VPE blends were prepared that showed excellent dry and wet bonding strengths and superior self-extinguishing flame retardancy. The highest bonding strengths, the maximum LOI value, and the lowest heat release rate in cone calorimetry tests were achieved by the VPE/VPU (80:20) blend due to the strong synergistic interpenetrating networks formed between the epoxy and PU macromolecules. The GC-MS analysis of the char residues indicated that the mechanisms for flame retardancy were a combination of the quenching effect from the phosphorus-containing free radicals and the diluting effect of the nonflammable gases in the gas phase, plus the formation of phosphorus-rich char layers in the condensed phase. This study showcased a highly promising approach to develop environmentally friendly high-performance flame-retardant chemicals using nontoxic vanillin as the starting material.