A bio-based adhesive from sorbitol and citric acid for sustainable plywood manufacturing

Traditional wood adhesives are mainly derived from non-renewable fossil resources, raising sustainability concerns. As a sustainable alternative, biomass-based adhesives have attracted attention due to their biodegradability and renewability; however, their poor water resistance and limited bond strength restrict broader applications. In this study, a bio-based plywood adhesive was developed from sorbitol and citric acid (CA) via esterification and characterized using FTIR, TGA/DTG, and SEM. The effects of sorbitol-to-citric acid (Sor:CA) molar ratio and reaction time on curing behavior and adhesive performance were evaluated. Increasing the Sor:CA molar ratio was more effective in enhancing the shear strength and water resistance of plywood than extending the reaction time. At a Sor:CA molar ratio of 1:3 and a reaction time of 60 min, the dry and wet shear strengths best satisfied the standard requirement (≥0.7 MPa, GB/T 9846-2015), suggesting that this fully bio-based adhesive may be a viable option for sustainable industrial applications.