Topology-controlled hyperbranched polyesters enable balanced soy adhesive strengthening and toughening

Soy protein (SP) adhesive have garnered significant attention due to their renewability and environmental friendliness. However, their inherent limitations—particularly poor water-resistant bonding strength and pronounced brittleness of cured adhesive layers—severely restrict large-scale applications. This study proposes a synergistic modification strategy utilizing hyperbranched polyester (HBPE). Through esterification reactions, HBPE with varying branching degrees was synthesized, and an innovative approach combining physical blending with epoxy-based chemical crosslinking was developed to achieve multi-level interfacial interactions between HBPE and SP molecules. When incorporating 10 wt% HBPE-3 coupled with 1.5 wt% 1,2,3-tris(glycidyloxy)propane, the modified plywood demonstrated a remarkable wet shear strength of 1.37 MPa (representing a 216 % enhancement over unmodified systems), while the toughness of cured adhesive films reached 0.53 MJ/m³ , demonstrating exceptional toughening effects. The topological structure of HBPE effectively disperses stress concentration, and the dynamic hydrogen-bonding network formed between its terminal hydroxyl groups and protein molecules significantly retards crack propagation. This research not only elucidates the structure-property relationship of hyperbranched molecules in strengthening and toughening SP adhesive but also provides theoretical foundations for developing bio-based adhesive that integrate high mechanical performance with sustainability. The findings exhibit promising application prospects in green packaging and engineered wood product industries.