Self-healing, flame retardant and UV resistant lignin-derived epoxy wood coating with a Schiff base structure

The traditional epoxy resin not only is flammable and non-recyclable and but also heavily dependents on petroleum resources, which cannot meet the requirements of fire prevention and sustainable development. In this study, a vanillin intermediate (VAP) with dynamic imine bond (C=N) was prepared by schiff base reaction between the lignin derivative vanillin (-CHO) and the cage-like polyhedral oligomeric silsesquioxane OA-POSS(-NH₂). Then, a biomass-based P-N-Si flame retardant (VAPD) was synthesized by adding 9,10-Dihydro-9-Oxa-10-Phosphaphenanthrene-10-Oxide (DOPO) into the VAP. Subsequently, the VAPD acted as curing agent of epoxy resin to prepare epoxy wood coatings (VAPDs/EP). The results showed that the VAPD-5/EP coating not only exhibited excellent self-healing property and was able to achieve 100 % healing within 35 min, but also presented distinctive UV-shielding performance. In addition, the VAPD-5/EP coating reached V-0 level of UL-94 test and got 29.3 % of limiting oxygen index (LOI). Compared with EP coating, the peak heat release rate (pHRR) decreased by 38 %. Furthermore, the VAPD-5/EP coating reached 6H level of hardness test and 4B level of adhesion test. A simple strategy for preparing self-healing flame retardant epoxy coatings with comprehensive properties for protection of wood materials was proposed in this study.