Dynamic covalent bonds enabled recyclable chitosan oligosaccharide-based wood adhesive with high adhesion and anti-mildew performances

Biomass wood adhesives have emerged as a promising alternative to traditional synthetic resins due to their ability to address issues related to formaldehyde pollution and reliance on petrochemical resources. However, these adhesives are generally not recyclable and require high curing temperatures. Herein, a novel eco-friendly, strong, and recyclable chitosan oligosaccharide (CS)-based wood adhesive named CS-PB was developed using CS, lignin-derived 3,4-dihydroxybenzaldehyde, and 1,4-phenylenediboronic acid. The cohesive strength and recyclability of the adhesive were significantly enhanced by the dynamic borate ester and imine networks formed through catalyst-free covalent cross-linking. The adhesive exhibited a maximum bonding strength of 5.60 MPa, surpassing many synthetic and biomass adhesives. Moreover, the recycled adhesive retained 88 % of its original strength. Even under extreme conditions such as 100 degrees C, -196 degrees C the CS-PB adhesive can still maintain high bonding strength. Notably, the CS-PB adhesive demonstrated low-temperature curing properties, achieving a high bonding strength of 5.21 MPa when cured at 90 degrees C, since imine bonds can be formed under mild conditions. Furthermore, the adhesive displayed excellent mildew resistance attributed to the synergistic effects of amino, boronic acid, and benzene rings. The proposed straightforward design strategy provides valuable insights for constructing high-strength and recyclable biomass adhesives.