Tough and multifunctional soy protein adhesive via nature-mimetic structural design.

In response to the growing demands for environmental protection and sustainable growth, the development of multifunctional, formaldehyde-free adhesives has emerged as a significant research direction within the field of materials science. Inspired by the robust structure of spider silk (composed of densely packed rigid crystalline regions and loosely arranged amorphous domains), this study employs epoxidized melamine prepolymer (EM) to react with active groups on soy protein, establishing a rigid cross-linked network. A flexible polyester, ESS, is incorporated into the adhesive system via hydrogen bonding, serving as a buffer layer to mitigate stress impact and dissipate strain energy. Compared with unmodified soy protein adhesive, the incorporation of a biomimetic structure in the adhesive system enhanced the prepressing strength of the SME/10ESS adhesive to 0.78 MPa, reflecting a 333.3 % improvement. Under dry and wet conditions, the shear strength reached 2.01 MPa and 1.12 MPa, showing increases of 42.6 % and 261.3 %, respectively. The work of adhesion increased by 212.5 %, reaching 225 mJ, indicating a significant improvement in toughness. Furthermore, the modified adhesive exhibited broad substrate compatibility and excellent water resistance, suggesting promising applications in wood processing, ceramic restoration, and related fields. The biomimetic modification also significantly enhanced mold resistance, enabling the fresh adhesive to remain mold-free for 12 days under controlled humidity. A life cycle assessment confirms that this biomimetic versatile bio-based adhesive represents a viable alternative to conventional petroleum-based adhesives. Its implementation is of critical significance in addressing the challenges posed by global resource scarcity and climate warming.