Lignin Colloids-Induced Interfacial Films Stabilize Water-In-Oil Isocyanate Emulsion Adhesives for Robust Wood Lamination

Constructing a water-in-oil (W/O) emulsion adhesive offers a promising strategy to mitigate bondline starvation and interfacial discontinuity resulting from excessive isocyanate penetration into wood in laminated systems. However, the reactive isocyanate-water heterogeneous interface leads to premature NCO consumption, uneven network formation, and interfacial defects. Therefore, reconciling adhesive retention with controlled interfacial reactivity remains a key challenge. Here, inspired by the structural logic of cell membranes in compartmentalizing phases and organizing interfaces, we design lignin colloids as multifunctional regulators in emulsions and establish a cooperative strategy that couples bulk rheological regulation with interfacial film engineering. Owing to their amphiphilic surface chemistry and steric effects, lignin colloids increase the apparent viscosity of the continuous isocyanate phase to suppress overpenetration while enriching at the isocyanate-water interface to assemble into an interfacial film. This film spatially limits direct phase contact and temporally buffers interfacial reactions. Consequently, the penetration depth in wood decreased from around 200 to 25 μm, the pot life of the emulsion was extended by 1.5-2-fold compared with the additive-free system, and about 80% of NCO was retained. A clear and continuous bondline structure was formed after curing, with dry shear strength increasing from 1.02 to 1.74 MPa. The strength retention rate after boiling water treatment reached 93%, and the system demonstrated greater environmental durability. Notably, the isocyanate usage can still be reduced by 30% while delivering enhanced bonding performance, highlighting the potential of this strategy for efficient wood adhesive systems with reduced isocyanate input.