Nacre‐inspired construction of soft–hard double network structure to prepare strong, tough, and water‐resistant soy protein adhesive
Yantao Xu, Yufei Han, Yue Li, Jing Luo, Jianzhang Li, Jianzhang Li, Jingchao Li, Jingchao Li, Qiang Gao
Abstract
Abstract Soy protein (SPI) adhesives are non‐toxic and eco‐friendly that can potentially replace traditional formaldehyde‐based adhesives to ease toxic gas emissions. The development of strong and toughness SPI adhesive benefits its bonding stability but is challenging. In this study, inspired by nacre structure, a soft–hard double network structure was constructed in SPI adhesive. The triglycidylamine (TGA) cross‐linked protein served as the hard phase to provide cohesion. In addition, the self‐synthesizing epoxidized rubber (ER) as soft phase cross‐linked protein and enhanced the interfacial force between hard and soft phase to dissipate energy during fracture, which improved the toughness of adhesive. The results showed that: compared with original SPI adhesive, the residue rate of SPI/4%TGA/3%ER adhesive increased by 7.9%, and the moisture absorption rate decreased by 16.7%. The dry and wet shear strength of the plywood prepared by SPI/4%TGA/3%ER adhesive increased by 58.9% and 160.4% to 1.86 and 1.38 MPa, which was higher than commercial polyamide‐epichlorohydrin modified SPI adhesive. The elongation at break increased by 55.2%–45%, the fracture energy increased by 233% to 2.96 MJ/m 2 , and the cracks on the adhesive surface disappeared, indicating that the strength, toughness, and water resistance of the adhesive were significantly improved. In this research, a soft–hard double network structure is constructed in a bio‐based adhesive to obtain excellent performance, this eco‐friendly adhesive opens up a new way to replace harmful formaldehyde‐based adhesives.