Preparation of a multi-functional soy protein adhesive with toughness, mildew resistance and flame retardancy by constructing multi-bond cooperation

Abstract

Faced with petrochemical resource shortages, partially replacing aldehyde adhesives with bio-based soy protein adhesives is crucial, yet modified versions still suffer from high interfacial brittleness and inadequate anti-mildew/flame-retardant properties. This study constructed a soy protein adhesive composite system based on multiple bonding interactions, including covalent crosslinking, hydrogen bond, and ionic bond. The crosslinker triglyceride amine (TGA) crosslinked with soy protein to form a cross-linked structure; sodium alginate (SA) interacted with soy protein to form hydrogen bond; Mg²⁺ chelated with SA and soy protein to form ionic bond. Among them, covalent crosslinking served as the backbone structure, providing water resistance and strength for adhesive, while hydrogen and ionic bonds acted as sacrificial bonds, dissipating energy and improving the toughness of the adhesive. Compared to the SPI adhesive, the dry and wet shear strength of SPI/SA/Mg²⁺/TGA adhesive increased by 66.09 % and 199.07 % reaching 1.91 MPa and 0.96 MPa, respectively, and the tensile strain increased by 23.5 %–32.4 %; the moldy time improved from 2 d to more than 15 d; the limit oxygen index increased by 20.8 %–29.0 %. This modification strategy collectively enhancing bonding toughness, mildew resistance, and flame retardancy to advance industrial utilization of soy-based adhesives and sustainable development of artificial board binders.