High‐Shear Mixing of Softwood Kraft Lignin in Aqueous Sodium Lignosulfonate: Stable Suspensions, Efficient Emulsification and Controlled Curing of Epoxy Adhesives

ABSTRACT

The transition toward safer and fully bio‐based wood adhesives requires both scalable processing methods and reactive formulations capable of competing with petrochemical systems. This work presents a simple and scalable route for producing waterborne colloidal suspensions of softwood kraft lignin (SKL) and lignosulfonate (LS) at solid contents reaching 55wt%, enabled by the dispersing action of LS under high‐shear homogenization without pH adjustment or organic solvents. The resulting lignin particle suspensions exhibit tunable particle size, zeta potential, and viscosity through modulation of the LS/SKL mass ratio. The lignin dispersions effectively stabilize oil‐in‐water emulsions as demonstrated with jojoba oil. Building on these properties, a fully biobased two‐component adhesive system was developed by combining the SL/SKL particle suspensions with glycerol diglycidyl ether. Lignosulfonate plays a critical role as an unconventional latent curing agent, extending pot life and enabling controlled reactivity. The adhesives display optimal lap‐shear strength with major wood failure above 4.5 MPa and maintain high mechanical performance after water immersion. Along with competitive adhesion performance, lignin‐glued plywood exhibited low VOC emissions, ranking them as recommended building materials according to a Swedish building materials assessment system. This study provides a scalable platform for valorizing technical lignins in formaldehyde‐free adhesives for engineered wood applications.