A Composite Whole-Biomass Tannin–Sucrose–Soy Protein Wood Adhesive with High Performance

Abstract

Whole-biomass adhesives are the research hotspot of wood adhesives andcan improve the competitiveness of adhesives. The tannin–sucrose adhesive studied by our research group shows good bonding performance, but poor bonding stability induced by low viscosity. In this study, the tannin–sucrose adhesive was modified by isolated soybean protein (SPI), the effect of the SPI substitution ratio for tannin on the properties of the tannin–sucrose–SPI composite adhesive was investigated, and the bonding mechanism was explored using Fourier-transform infrared spectroscopy (FT-IR), thermogravimetry (TG), X-ray diffraction (XRD), and gas chromatography–mass spectroscopy (GC–MS). The results showed that: (1) when the SPI substitution ratio was above 40%, the viscosity of the composite adhesive increased significantly, which effectively avoided adhesive leakage. (2) The tannin–sucrose–SPI composite adhesive displayed high bonding performance and water resistance. (3) The FTIR and GC–MS results revealed that the curing mechanism of the tannin–sucrose–SPI adhesive was very complicated, but it was certain that the conversion of sucrose into furan compounds, especially 5-hydroxymethylfurfural (5-HMF), was the core of the cross-linking reaction of the adhesive when elevating temperature. (4) The macromolecules and high reactivity of SPI compensated for the shortage of high temperature required for the conversion of sucrose into furanic cross-linkers so that the tannin–sucrose–SPI adhesive experienced an efficient curing reaction at a low temperature, and the reaction degree and thermal stability of the curing product increased.