Candy Wood: Bioadhesive Based on Citric Acid and Glucose With Additives (Lignin, Starch and Glycerol)

ABSTRACT This study investigated and evaluated bioadhesives formulated with citric acid and glucose, modified with lignin, starch, or glycerol, assessing their potential application in plywood bonding. The formulations were characterized in terms of solids content, rheological behavior, and functional groups (FTIR), while the produced panels were evaluated for their physical, mechanical, and microstructural properties. All bioadhesives exhibited thermal stability and pseudoplastic behavior, which is suitable for adhesive spreading and hot‐pressing processes. FTIR analysis confirmed the formation of ester bonds between citric acid and hydroxyl‐rich components, indicating effective crosslinking. Regarding physical properties, starch increased the susceptibility of panels to water absorption (53% after 2 h and 78% after 24 h), whereas glycerol showed low initial water absorption (27%) but high thickness swelling (126% after 2 and 24 h). Among the treatments, the starch‐modified adhesive achieved the best mechanical performance (MOR of 23.5 MPa and MOE of 2720 MPa), which was attributed to the formation of a denser polymeric network and a continuous glue line. Lignin also enhanced mechanical performance and bioadhesive homogeneity, while glycerol increased viscosity and flexibility but resulted in intermediate strength due to its plasticizing effect. Although the mechanical and rheological performance was promising, the high intrinsic acidity of citric‐acid‐based systems remains a critical aspect that must be addressed for industrial implementation, particularly regarding wood durability and long‐term panel stability. Overall, the results demonstrate that bioadhesives are promising alternatives for the plywood industry, offering satisfactory performance while reducing environmental impact and enabling the use of renewable raw materials.