An environmentally friendly bio-based wood adhesive prepared via a green and mild method inspired by insect cuticle

Biobased adhesives have the potential to replace traditional adhesives because they are sustainable, biodegradable, and environmentally-friendly. This work presents a simple and effective strategy inspired by the insect exoskeleton hardening mechanism to react pyrogallol (PG, derived from gallnut) and branched polyamines (PAXN) into a high-performance and environmentally-friendly wood adhesive. Pyrogallol was oxidized (donated as OPG) with the aid of NaOH at room temperature to convert its phenolic hydroxyl group to quinone group, then the quinone group is cross-linked with PAXN by a Schiff base reaction to obtain the OPG-PAXN adhesive. The bonding performance of the bio-based adhesive was studied systematically, which shows that the optimal mass ratio of OPG/PAXN is 1:1, and the best performance was obtained with a solid content of 50%. The dry strength of the OPG-PA6 N adhesive reached 2.22 MPa, and the wet strength increased from 0 to 1.85 MPa. Furthermore, 13C NMR, FTIR, XPS, and other characterizations showed that OPG-PA6 N network was formed by imine bond. TG and DSC results indicated that the thermal properties of OPG-PA6 N adhesive was significantly enhanced compared with those of OPG or PA6 N. The proposed bio-based adhesive is expected to become a potential substitute for the traditional formaldehyde-based adhesive.