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

Abstract

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.