H2O2-mediated tannin bio-based wood adhesive inspired by starfish structure and phenol-amine synergy

High-performance formaldehyde-free bio-based wood adhesives are extremely attractive because of the friendliness and sustainability of their ingredients and resources. This work reports a phenol-amine synergistic tannin bio-based adhesive inspired and designed by insect exoskeleton hardening and starfish structure. The phenol-amine synergistic strategy is based on Schiff base reaction and Michael addition between the benzoquinone group of tannin acid (TA) and the nucleophilic amino group of polyamines (PAXN, X = 4, 5 and 6, X represent the number of amino-terminal groups), which is supplemented by oxidation-induced quinone cross-linking in TA and the combination of covalent and non-covalent bonds. The proposed TAPA wood adhesives with the three-dimensional dense cross-linking network may dissipate stress via hiding sacrificial bonds, which can form a compact glue film to prevent the infiltration of water molecules as well as increase thermal resistance. FT-IR, XPS, and solid 13C NMR demonstrated the tannin-based phenol-amine network was formed by cross-linking imine covalent bonds. DSC, TG, and DMA revealed reduced melting and glass transition temperatures, as well as improved thermal stability, which are conducive to the cross-linking and curing of adhesives. In detail, the dry lap shear strength of TAPA adhesive increased by 170% from 0.8 MPa to 2.16 MPa compared with pure TA adhesive by using poplar veneer as wood substrate; and the wet lap shear strength made a breakthrough from 0 to 1.06 MPa, exceeding the minimum requirement (0.7 MPa) defined by the China national standard (GB/T 17657–2013). Given this, a high-efficiency, green, and economic phenol-amine synergistic strategy are beneficial to the development of formaldehyde-free bio-based wood adhesives and multifunctional application of agricultural and forestry residues.