Citric acid/chitosan adhesive with viscosity-controlled for wood bonding through supramolecular self-assembly

Developing bio-based sustainable wood adhesives is significant as a substitute for petroleum-derived adhesives. However, the existing bio-based adhesives have disadvantages of complex fabrication, uncontrollable viscosity, and poor water resistance. Herein, we developed a citric acid/chitosan adhesive with viscosity-controlled and water-resistant features by one-step dissolution at room temperature based on the supramolecular self-assembly strategy. Different wood products (plywood, laminated veneer lumber and particleboard) with superior performance were prepared by applying that adhesive on veneer and wood particles (fine and rough particles). The plywood test results showed that the citric acid/chitosan adhesive had dry and wet shear strengths outperforming the China National Standard (GB/T 9846-2015, ≥0.7 MPa), reaching 2.1 and 1.1 MPa, respectively. The adhesion mechanism was mechanical interlocks and cross-linking of citric acid/chitosan in adhesives with those in the cell wall. This work provides high promise for alternatives to traditional unsustainable wood adhesives (urea-formaldehyde, melamine-urea-formaldehyde and phenolic resins) for fabricating different wood products.