A bio-based adhesive reinforced with functionalized nanomaterials to build multiple strong and weak cross-linked networks with high strength and excellent mold resistance

With the increasing attention to environmental concern, the reduction of fossil energy source and the demand of actual industrial production, there was strong demand to develop green, sustainable, and low-cost bio-based adhesive. Here, inspired by the self-assembly of nature to produce characteristic materials, multifunctional CA/TA/FC nanospheres were prepared from cinnamaldehyde (CA), tannic acid (TA), and ferric chloride (FC). Soybean meal (SM) adhesive was synergistically modified by nanospheres and sulfhydrylated nanotubes (HNTs@SH) through multiple networks and nanofilling strategies. The cross-linked network of the obtained SM-CA/TA/FC-HNTs@SH adhesive was reinforced by Schiff base reaction, acetal reaction, disulfide bonds (SS) generation/exchange, electrostatic interaction, ionic cross-linking, and hydrogen bond formation. Compared to SM adhesive, the dry/wet shear strength of the SM-CA/TA/FC-HNTs@SH adhesive was increased by 47.0 % (1.64–2.41 MPa) and 160.7 % (0.56–1.46 MPa), water resistance was increased by 9 % (68.1 %-77.1 %), viscosity was reduced to acceptable value (33.0 Pa·s), and effective storage time was extended by 50 days (d). Compared to currently used SM-PTGE adhesive, the cost was reduced by 26.7 % (2200 RMB/Ton), showing great potential as an alternative to the widely used formaldehyde resin adhesive. The combination of self-assembly, nano-filling, and multi-networking strategies also provided ideas for the enhancement and multi-functionalization of other engineering materials.