Dual-Network Nanocross-linking Strategy to Improve Bulk Mechanical and Water-Resistant Adhesion Properties of Biobased Wood Adhesives

Biomass-derived protein adhesives have gained considerable attention as a replacement for formaldehyde-based resins in industry. However, for biobased structural adhesives, water-tolerance polymeric structures were highly necessary to realize adhesion and cohesion behaviors. In this work, a new dual-network soy-based adhesive consisting of nanocross-linkers (aldehyde- and dopamine-bearing, cellulose nanofibers, OCNF-CA) was successfully designed and prepared, and the cross-linking structure–property relationship of the adhesive was systematically studied. The double cross-linked structure considerably facilitated the preferential detachment/rupture of the rigid protein chain network, therefore significantly improving the filler dispersion and energy dissipation efficiency. Strong and tough mechanical performance was achieved, with a maximum tensile strength of 8.42 MPa and a toughness of 6.06 MJ/m3. Thanks to the tailored moisture-insensitive adhesion interface resulting from the sufficient free-catechol groups on the optimal network, this dual-network adhesive exhibited high and stable adhesion properties as determined by the ultimate shear stress for glued plywood. This work provides a novel strategy to design a hybrid cross-linking network for preparing high-performance environmentally friendly adhesives in wood-based panel industries.