Preparation of a Brown Alga-Inspired, Multifunctional, and Bionic Soy Protein Adhesive Based on Bamboo Cellulose Nanofiber and Rosin Acid

While the promising application prospects of soy protein adhesives (SPI) as green alternatives to formaldehyde-based resins, poor bonding strength and unsatisfactory water resistance restrict the practical application. Inspired by brown alga bionics and organic–inorganic hybridization system, a bionic and multifunctional soy protein adhesive (SPI-RA-BCNF-MMT) was prepared utilizing rosin acid derivative (RA), bamboo cellulose nanofiber (BCNF), and montmorillonite (MMT). Optimal formulation SPI-10RA-6BCNF-4MMT optimized by response surface methodology presented excellent dry and wet shear strengths (2.41 and 1.41 MPa), which were increased by 270% and 231% compared to pure SPI. Moreover, the strength of the modified adhesive far exceeded the China National Standard (0.70 MPa). Molecular docking strategy and finite element analysis also confirmed strong interactions within SPI-10RA-6BCNF-4MMT. In addition, SPI-10RA-6BCNF-4MMT exhibited exceptional water and organic solvent resistance, owing to the dense cross-linking structure. Remarkable coating properties enabled SPI-10RA-6BCNF-4MMT to be coated evenly in dry and wet environments. Furthermore, SPI-10RA-6BCNF-4MMT showed outstanding flame-retardant properties, improving safety in practical use. Meanwhile, life cycle assessment of SPI-10RA-6BCNF-4MMT revealed environmentally friendly features, such as low formaldehyde pollution and greenhouse gas emission. Therefore, this proposed green, multifunctional, and bionic adhesive demonstrated an eco-conscious alternative to traditional formaldehyde-based resins for the large-scale fabrication of wood composite materials.