Tough protein based adhesive reinforced by molecular spring strengthening strategy.

[Display omitted] • A new design strategy of crosslinker inspired by spring structure was proposed. • A new adhesive formulation substitute for petroleum-based adhesives was proposed. • A tough keratin-based adhesive with zero formaldehyde-emission was prepared. • The adhesive exhibited high adhesion to numerous types of substrates. It is of great importance but still a great challenge to develop bio-based environmental adhesives for industrial applications. In this study, inspired by the adhesion structure of lignin and spring mechanics, a new biomimetic strategy was proposed to prepare high bonding strength, formaldehyde-free and petroleum resource-independent adhesive from biomass. Through Schiff base and Michael addition reaction between the quinone of oxidized demethylated lignin (DL) and the amino and sulfhydryl groups of soybean protein isolate (SPI) with helix chain, SPI was grafted onto DL to form reinforcement structure and crosslinker with molecular spring structure (namely SDL). Cleavage of the disulfide bonds of keratin and introduction of SDL reconstituted a strong cohesive crosslinking network (KPT-SDL), in which the α -helical peptide chain in SDL was stretched and the intramolecular hydrogen bonds were broken under tensile force, thus achieving energy dissipation and significantly improving the shear strength and toughness of the keratin-based adhesives. The maximum wet strength of the wood-based panel prepared by KPT-SDL adhesive reached to 1.22 MPa, which was comparable to the level of industrial adhesives and 197.56% higher than the original keratin-based adhesive. In addition, KPT-SDL presented high adhesion to numerous types of substrates, including steel and ceramic. This study provided a green and effective biomimetic strategy for high value-added keratin to promote the development of strong and tough composites, which had a good value of frontier research and industrial development. [ABSTRACT FROM AUTHOR]