Cross-linking oxidized rice straw and chitosan for preparing a fully bio-based adhesive with exceptional...

Bio-based adhesives hold tremendous potential as sustainable substitutes for petroleum-based adhesives. Currently, a considerable amount of rice straw is abandoned. The utilization of rice straw in bio-based adhesive preparation promotes its reuse. Herein, an oxidized straw flour-chitosan (OSF-CS) adhesive was synthesized via a one-pot method by combining oxidized straw flour (OSF) with chitosan (CS) solution. The oxidation of straw using sodium periodate generated quinone and aldehyde groups. These quinone and aldehyde groups engaged in covalent reactions with the amino groups on chitosan, facilitating the formation of a three-dimensional covalent cross-linked network between oxidized straw and chitosan, ultimately yielding the OSF-CS adhesive. This was confirmed by FTIR, XPS, ¹³C NMR, and SEM. The boiling water lap shear strength of the adhesive reached 1.42 MPa, meeting the Type I plywood requirements in the Chinese national standard (GB/T 9846-2015). The cross-linking ability of oxidized straw to chitosan was observed to change in a wave-like manner with the extension of oxidation time. This study experimentally confirmed that the primary component cross-linked with chitosan in the OSF-CS adhesive is the oxidized lignin in oxidized straw. This research provides a method for preparing fully bio-based wood adhesives with strong water-resistant bonding performance using raw vegetation materials.