Breaking the Barrier of High Curing Temperature: Efficient Caramelization for Fructose-Based Adhesives in a One-Pot Process

Driven by sustainable development goals, the wood-based panel industry increasingly favors renewable biomass-based and formaldehyde-free adhesives. Saccharides, owing to their renewable environmental friendliness and high reactivity, have garnered attention for green adhesive development. However, existing saccharide-based adhesives face challenges due to demanding curing conditions (hot-pressing temperature ≥160 °C), limiting their industrial application. In this study, a fructose and toluene-4-sulfonic acid adhesive (FT adhesive) was prepared by a simple one-pot process. FT adhesive can be hot-pressed at 110 °C to prepare plywood in line with the China National Standard GB/T 9846–2015 (wet strength ≥0.7 MPa). Compared with other saccharide-based adhesives, FT adhesives show superior curing efficiency while maintaining high bonding strength. During the synthesis phase, fructose reacts with toluene-4-sulfonic acid at lower temperatures to produce various active compounds, including 5-HMF and its derivatives, formic acid, acetic acid, and furan compounds. These compounds undergo condensation reactions during high-temperature curing, forming polyfurans, humin polymers, and other insoluble polymers predominantly bonded by C–O–C, C–O, and C═O linkages. Additionally, toluene-4-sulfonic acid acts as a catalyst and an enhancer in both synthesis and curing phases, facilitating the conversion and cross-linking of 5-HMF and its derivatives. This process results in a robust and dense network structure, significantly enhancing the adhesive performance of FT adhesives at lower curing temperatures (110–130 °C). This research offers insights into the development of efficient and environmentally friendly saccharide-adhesives for wood-based panels.