Synthesis of lignin-tannin biobased flame-retardant adhesives via self-assembly strategy

With the increasing demand for green materials, biomass adhesives combining flame retardancy and water resistance have become a key breakthrough in the upgrading of wood structural materials.Lignin and tannic acid are natural biomass raw materials for preparing flame-retardant biomass adhesives. However, their disadvantages of poor water resistance and bonding performance severely limit their applications. This study prepares the flame-retardant and water-resistant adhesive LT/CP@TP by adopting a combination of self-assembly, grafting treatment, and cross-linking methods. The adhesive formulation consists of glyoxalated lignin, tannic acid, chitosan, phytic acid, polyethyleneimine, and a TGA(triglycidylamine) epoxy crosslinker.Subsequently, the curing behavior characteristics, combustion behavior, and thermal stability of the LT/CP@TP adhesive were analyzed. The functional group analysis was used to clarify the reaction mechanism involved. The total heat release of the wood coated with the cured LT/CP@TP is significantly reduced by 49.8 % compared with that of pure wood and the carbon monoxide generation rate is reduced by 72 %. The Limiting Oxygen Index (LOI) of poplar veneers with the LT/CP@TP adhesive coated on their surface and cured reaches 29.2 %. The dry shear strength of this adhesive and the shear strength after being immersed in hot water at 63 °C for 3 h are 1.82 MPa and 0.98 MPa respectively. This study provides a potential strategy for preparing lignin-tannin-based adhesives with flame retardancy, water resistance, and good adhesive properties.