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Lignin is a phenolic polymer, making it a sustainable alternative to phenol for synthesizing lignin–phenol–formaldehyde (LPF) adhesives. However, technical lignins produced in pulping or biorefining processes are generally highly condensed and have low reactivity, limiting their uses in synthesizing phenolic-based adhesives. Herein, we report a two-step strategy to produce lignin-based wood adhesives with industrially available technical lignins through hydrodeoxygenation followed by acid-mediated methylolation of aromatic C2/6 positions to improve the flowability, water resistance, and crosslinking ability of lignins. We demonstrated that this biobased lignin–formaldehyde adhesive had a lighter color and far better adhesion performance compared to traditional LPF resins prepared from base-mediated methylolation of lignins. Mechanistic investigation suggests that the chemical crosslinking of methylolated lignin to form diarylmethane structures and the physical interlocking interaction at the interfaces of wood veneers contribute to the strength of plywood. [ABSTRACT FROM AUTHOR]

γ-valerolactone (GVL)/H 2 O/acid solvent mixtures has been used in chemical pretreatment of lignocellulosic biomass, it was claimed that GVL lignins were structurally close to proto (native) lignins, or having low molecular weight with narrow polydispersity, however, the structural changes of GVL lignins have not been investigated. In this study, β-O-4 (β-aryl ether, GG ), β-5 (phenylcoumaran), and β-β (resinol) lignin model compounds were treated by an acidic GVL-H 2 O solvent system, a promising pretreatment of lignocellulose for biomass utilization, to investigate the structural changes possibly related to the lignin involved. NMR characterization of the products isolated from the treated GG indicated that a phenyl dihydrobenzofuran, having typical C-H correlations at δ C /δ H 50.74/4.50 and 93.49/4.60 ppm in its HSQC spectrum, was produced from GG . In the pretreatment, the released formaldehyde from GG reacted fast with GG to form a novel 1,3-dioxane intermediate whose characteristic HSQC signals were: δ C /δ H 94.15-94.48/4.81-5.18 ppm and 80.82-83.34/4.50-4.94 ppm. The β-5 model, dihydrodehydrodiconiferyl alcohol, was converted into phenylcoumarone and stilbene having benzaldehyde that resulted from the allyl alcohol side chain. The β-β model, syringaresinol, was isomerized to form a mixture of syringaresinol, epi-, and dia-syringaresinol although being degraded slightly.