Extended Data Fig. 3: Comparison of adhesion performance of FPLs with different condensation degrees.

a, Schematic illustration of the preparation process of three-layer plywood. Each layer was oriented with its grain perpendicular to that of the adjoining layer. b, The photograph of a bonding strength test. c, d, Effects of formaldehyde loadings (c) and extraction temperatures and times (d) on the condensation degree and adhesion performance of FPLs. Extraction temperature and time are the reaction temperature and time required for cooking biomass in a reactor to isolate lignin from biomass. At a specific formaldehyde loading, low extraction temperature or short extraction time facilitate to reduce the condensation of isolated FPLs and improve their adhesion performance. A higher temperature (140 vs. 80 °C) facilitated FPL extraction in shorter time (20 vs. 300 min), meanwhile maintaining the relatively low condensation degree. Although the wet strength of FPL-bonded plywood went down from 1.17 ± 0.05 MPa (mean ± standard deviation; 80 °C, 300 min) to 1.00 ± 0.06 MPa (mean ± standard deviation; 140 °C, 20 min), which was still higher than 0.7 MPa. In contrast, FPL that was extracted at 160 °C for 10 min had a monomer yield of only 1.9%, showed no adhesion. e, Yields of monomers resultant from hydrogenolysis of FPLs isolated under different conditions. The structures of silylated lignin monomers (M1–M9) were given in Extended Data Fig. 2. The hot-pressing conditions of lignin adhesives used to prepare plywoods in c and d were 190 °C (hot-pressing temperature), 8 min (hot-pressing time), 1.5 MPa (hot-pressing pressure), and 100 g glue·m⁻² (glue application level).