Robust Soy Protein/Zein Adhesives by Molecular Entanglement and Organic–Inorganic Hybridization

ABSTRACT Plant protein adhesives are promising alternatives to aldehyde‐based adhesives for wood‐based panels. These adhesives mitigate indoor formaldehyde pollution and promote the sustainable development of wood adhesive. However, plant protein adhesives have been suffering from the intrinsic brittleness that can lead to low bonding strengths and a poor bonding stability. To address this issue, herein, a robust bio‐adhesive using zein, soybean protein (SPI), ammonium salt‐modified laponite (OL), self‐made crosslinker triglycidylamine (TGA) is developed. Zein dissolves in sodium dodecyl sulfate solutions to form a molecular entanglement structure with themselves and SPI molecules. OL and TGA are then added to create an organic–inorganic hybridization structure. The as‐prepared adhesive exhibits a break strain ∼24‐fold higher than that of the SPI adhesive and ∼2.14‐fold higher than that of commercial urea‐formaldehyde (UF) adhesives. Consequently, the cured adhesive film is both bendable and foldable, while cured SPI and UF adhesive film is easily broken when bending and folding. The enhanced toughness is mainly attributed to molecular entanglement and the organic–inorganic hybridization structure in the engineered bio‐adhesive, which effectively dissipates energy under external forces. Moreover, the resulting adhesive exhibits a 101.8% increase in wet shear strength, a 200% increase in work of adhesion, long‐term mildew resistance, and excellent soil degradability compared with SPI adhesives. This study provides a promising and practical approach for enhancing the toughness of biomass adhesives and composites, thereby facilitating their broader application.