Network-mediated dispersion of lignin in cellulose nanocrystal suspensions as strengthening mechanism for wood adhesives.

Kraft lignin exhibits significant potential for adhesive applications; however, its valorization in water-based systems remains challenging due to poor dispersion and hydrophobicity. Herein, we report a facile and effective approach for preparing a kraft lignin suspension using cellulose nanocrystals (CNCs). The interactions and structures were investigated using surface analysis, rheology, and optical observations. Oscillation tests reveal that hydrogen-bond-driven gelation of the percolated CNC network is critical for physically stabilizing lignin without chemical modification. Building on this mechanistic understanding, we evaluated the influence of CNC-lignin structures on the curing behavior, thermal stability, and adhesive performance of urea-formaldehyde (UF), the most widely used wood adhesive. The resulting composite exhibited lap-shear strengths of up to 5.2 MPa, demonstrating the potential of CNC-mediated lignin stabilization as a high-performance and sustainable strategy for water-based adhesive formulations.