Biobased Flame-Retardant Epoxy Adhesive Based on Resveratrol: Phosphorus–Nitrogen Synergistic Flame Retardancy and Property Investigation

In the face of the increasing shortage of petroleum resources and the safety challenges brought by the flammability of epoxy adhesives, the development of flame-retardant epoxy adhesives based on renewable resources has become an urgent demand in the field of materials. In this study, resveratrol derived from biomass was used as a raw material to prepare resveratrol-based epoxy resin (RSEP). Building on this, a biobased flame-retardant curing agent (FVD) was designed and synthesized using vanillin (VN) and glutamic acid (GLU) as raw materials, combining the flame-retardant properties of DOPO with a biomass derived structure. By simultaneously introducing nitrogen and phosphorus, synergistic nitrogen phosphorus flame retardancy was achieved. The biobased epoxy adhesive system had good mechanical properties and excellent flame retardancy, compared with RSEP/FVD-0, the storage modulus of RSEP/FVD-1.0 was improved, and the limiting oxygen index was increased from 26.6% to 33.9%, UL-94 test from NR to V-0 level, and in the wood coating experiment still maintain V-0 level of flame-retardant grade, showing practical value. The cone calorimeter test results further confirmed that the fire safety was improved, and the peak heat release rate (PHRR) and total heat release (THR) decreased by 72.3% and 60.2%, respectively. After combustion, the carbon residue layer is denser and more uniform, and the degree of graphitization is higher. This work provides a new idea for the preparation of biobased phosphorus nitrogen synergistic flame-retardant epoxy adhesive.