Dual-Metal Synergy in Soy Protein Adhesives: Silver and Zinc Ions Co-Anchor on a Nanoporous Framework for Enhanced Bonding, Water Resistance, and Mold Resistance

Soy protein (SP) adhesives represent a promising environmentally friendly binder; however, their practical application is hindered by inherent limitations, including poor water resistance, low mechanical strength, and vulnerability to microbial degradation. In this study, we synthesized a novel ZIF-8-Ag composite using a straightforward room-temperature method and incorporated it into soy protein isolate (SPI) to create a high-performance biobased adhesive. Morphological and structural analyses confirmed that Ag nanoparticles were successfully immobilized on the ZIF-8 framework without compromising its structural integrity. SPI-based adhesives modified with varying ZIF-8-Ag loadings (0–1.0 g per 10 g SPI) demonstrated significantly enhanced viscosity, bonding strength, water resistance, thermal stability, and mold resistance. The optimal performance was achieved with a ZIF-8-Ag loading of 0.8 g, where the dry and wet shear strengths reached 4.9 and 3.72 MPa, reflecting improvements of 236.49% and 324.21%, respectively, compared to the unmodified SPI adhesive. Antimold stability increased by 143%, resulting in a residual rate of 89.17%. This enhancement is attributed to the synergistic interaction between Ag+ and Zn2+ ions with functional groups in SPI, which facilitates the formation of a denser cross-linked network. This network restricts molecular mobility and establishes a protective barrier against moisture and microorganisms. This study presents a sustainable development strategy for designing high-performance biobased adhesives.