Fabricating a fully lignin-based adhesive from in-situ phenolation of lignocellulosic biomass

Lignin, as the main by-product from the chemical pulping process, has suffered serious structural damage, resulting in increased condensation and reduced activity, which makes it difficult to realize high-valued applications. Herein, we proposed a facile strategy for preparing fully lignin-based adhesive directly from lignocellulosic biomass via in-situ phenolation. The in-situ phenolation that occurred during the delignification process endowed the extracted lignin with numerous phenolic hydroxyl groups, enabling the highly reactive lignin to possess the possibility as a natural lignin-based wood adhesive. The process of fabricating the lignin-based adhesive could be achieved via a simple mixing of the in-situ phenolated lignin and alkali lignin in basic solution. The plywood products prepared with the lignin-based adhesive exhibited superior performance with dry and wet bonding strengths reaching 3.09 MPa and 0.92 MPa, respectively. Mechanistic analysis revealed that hot pressing induced lignin self-polymerization and formation of new ether linkages, contributing to the enhanced adhesion. Compared with reported lignin-based adhesive systems, this aldehyde-free formulation achieved competitive bonding performance without aldehyde-based crosslinkers, indicating its potential as a sustainable alternative to formaldehyde-based wood adhesives. This work presents a facile strategy for producing fully lignin-based adhesives from biomass and provides insight into formaldehyde-free wood adhesive systems.