Covalent Engineering of Lignin-Rubber Networks: Aminated Lignin as a Reactive Modifier for Epoxidized Natural Rubber Wood Adhesives

Although epoxidized natural rubber (ENR) and lignin have shown promise as components of biobased adhesives, their practical application still faces several technical challenges. The key challenge lies in promoting efficient reactions between the epoxy groups on the ENR molecular chain and the active functional groups of lignin, while avoiding complex chemical modifications or expensive catalysts, to form a stable, high-strength cross-linked network, thereby producing high-performance and environmentally friendly lignin-based adhesives. This study develops a highly reactive ENR/lignin composite adhesive system. The system uses ENR as the matrix and aminated lignin modified with silane coupling agent KH550 as the cross-linking agent, relying on the efficient reaction between epoxy groups and amino groups to achieve cross-linking. Experimental results show that the shear strength of the adhesive under dry conditions is 1.91 ± 0.20 MPa, and even after soaking in water at 63 °C for 3 h, the shear strength remains at 1.24 ± 0.04 MPa. Compared with traditional phenolic and urea-formaldehyde resins and other reported lignin-based adhesives, the ENR/aminated lignin composite adhesive not only exhibits superior bonding performance but also has stronger environmental benefits. All components are derived from renewable biomass resources, and the manufacturing process does not release formaldehyde. This work proposes a novel strategy for advancing green and efficient formaldehyde-free adhesive technologies.