Development of a high-performance glyoxal–tannin–epoxy wood adhesive modified with triethylenetetramine

➢ Construction of a robust 3D cross-linked network within TGT-TETA. ➢ Optimal R=8: 2: 1: 1.5 yields max strength: 1.75/1.66/1.12 MPa (dry/hot/boiled). ➢ Inherent antifungal properties are integrated into the TGT-TETA adhesive system. ➢ Significant enhancement in flame retardancy is achieved through the cross-linked network. Due to challenges such as fossil resource scarcity and tightening environmental regulations, the wood industry requires the development of formaldehyde-free adhesives based on renewable resources. This study reports the development of a formaldehyde-free wood adhesive based on biomass-derived tannin, glyoxal, triethylenetetramine (TETA), and glycerol triglycidyl ether (GTE). By introducing GTE as an epoxy-functionalized modifier to the TETA-modified system, the TG resin system (tannin–glyoxal prepolymer) achieves a highly crosslinked three-dimensional network through a synergistic mechanism involving amine–aldehyde condensation and the ring-opening reaction of epoxy groups. Optimization studies revealed that a mass ratio of TETA to tannin of 1:1.5, combined with a precise dosage of GTE, facilitates the formation of a stable C–N and C–O–C covalent network, which significantly improves both mechanical strength and thermal stability. Plywood samples bonded with this adhesive demonstrated superior performance, achieving shear strengths of 1.75 MPa (dry), 1.66 MPa (hot water), and 1.12 MPa (boiling water). These values comfortably exceed the Chinese National Standard (GB/T 17657) requirements for Type II panels (≥ 0.7 MPa), outperforming most previously reported tannin-based adhesives. This work provides a reliable, high-performance technical pathway for the industrial manufacturing of formaldehyde-free wood-based panels. Download: Download high-res image (288KB) Download: Download full-size image