Thermal-mechanical triphasic assembly enables ultra-strong soy protein adhesives via biomass welding

The development of sustainable adhesives that combine high mechanical strength with environmental compatibility remains a challenge. Here, we report a simple strategy to fabricate ultra-strong, fully bio-based adhesives from soy protein isolate (SPI) and water. Through optimized hot pressing (160°C, 1.5 MPa, 8 min), the plywood achieves a record shear strength of 15.46 MPa, surpassing phenol-formaldehyde resins. Multiscale characterization reveals a welding-inspired triphasic assembly mechanism: lignin fluidization (150°C) enables interfacial penetration, cellulose self-crosslinking reinforces the scaffold, and covalent C–N/C–O bonding locks SPI-wood interfaces. This approach eliminates synthetic modifiers, exhibits closed-loop emissions (primarily H 2 O/CO 2 ), and demonstrates industrial viability. Our work addresses critical challenges in biomass composites and provides a framework for energy-controlled interfacial fusion in sustainable materials, with potential in smart materials and green engineering.