Preparation of high-performance antibacterial/antifungal citric acid-starch adhesives based on physical entanglement and chemical crosslinking.

Starch-based wood adhesives are widely used as environmentally friendly and formaldehyde-free alternatives in the manufacturing of wood products. However, their poor water resistance and inability to inhibit bacterial/fungal growth limit their practicality. To address this issue, a physicochemical double-crosslinked network structure between citric acid, starch, and wood was prepared in this study by physically entangling the wood structure and chemically crosslinking the starch molecules, with citric acid preventing the activity of various enzymes and denatured proteins within microbial cells, thereby inhibiting bacterial and fungal growth. In water resistance cycling tests, the resulting esterified starch plywood demonstrated a 47.6 % and 13.2 % increase in water resistance compared with starch plywood and commercially available phenolic resin plywood, respectively. In addition, the tighter intermolecular bonding in the crosslinked structure results in a 31 % increase in heat resistance. The physical "nailing" and chemical crosslinking between the adhesive and the wood improved considerably the bonding strength to 98.36 %. The dual role of the physicochemical crosslinking of starch adhesives provides a straightforward strategy for the preparation of inexpensive, water-resistant, and fungal/bacterial-resistant starch adhesives, thus contributing to the promotion of starch adhesives.