Green bio-adhesives production from wheat straw lignin via deep eutectic solvent extraction and mild modification

Traditional wood adhesives such as phenolic and urea-formaldehyde, which continuously release carcinogenic formaldehyde during production and use, seriously endanger human health and pollute the environment. Therefore, the development of high-performance bio-based adhesives without formaldehyde has become a research hotspot in the field of wood processing. This study developed a green and efficient strategy for preparing bio-based formaldehyde-free adhesives via deep eutectic solvent (DES)-assisted hydrothermal extraction of wheat straw lignin and its modification. The extraction process featured mild conditions (120 °C, 3 h) with high energy efficiency, achieving a lignin yield of 80.2 ± 1.06% without harsh reagents. Notably, oxidative modification of lignin used only hydrogen peroxide (without additional chemicals), achieving a non-toxic and pollution-free treatment while effectively introducing carboxyl groups to enhance reactivity. The oxidized recovered lignin (ORL) reacted with polyvinyl alcohol (PVA) and glycerol triglycidyl ether (GTE) to form a stable cross-linked network. The oxidized lignin adhesive (OLA) exhibited a wet shear strength of 1.07 ± 0.22 MPa, meeting the Chinese national standard GB/T 9846-2015 (≥0.7 MPa). This work emphasizes the mild and green extraction and modification process, providing a sustainable method for the value-added utilization of straw and promoting the industrialization process of environmentally friendly wood adhesives.