Baking-induced structural activation of starch for preparing high-strength and water-resistant starch-based adhesives for plywood applications.

Abstract

Starch adhesives have emerged as important alternatives to traditional petroleum-based adhesives owing to their renewability and environmental compatibility. However, poor water resistance and insufficient bonding strength limit their practical application. In this study, a novel high-temperature thermo-oxidative baking activation strategy was developed to enhance starch reactivity for preparing high-performance plywood adhesives. During baking, the number-average molecular weight (Mn) decreased from 1.61 × 105 to 1.07 × 105 g/mol, and the relative crystallinity decreased from 30.1% to 25.8%, indicating that baking induced partial cleavage of starch molecular chains and disrupted the ordered crystalline structure. Meanwhile, X-ray photoelectron spectroscopy (XPS) analysis showed that the O1s content increased from 33.41% to 55.77%, and the relative content of CO groups reached 15.44%. These results indicated that baking induced thermo-oxidation and increased oxygen-containing structures on the starch, thereby enhancing starch chemical reactivity. The baking-activated starch was subsequently grafted with itaconic acid and crosslinked with furfuryl alcohol to form an adhesive network structure. The optimized adhesive exhibited a wet shear strength of 1.48 MPa, representing a 289.5% improvement over the pure starch adhesive. Moreover, its moisture absorption rate decreased from 3.21% to 0.47%, indicating improved moisture resistance. Overall, this high-temperature thermo-oxidative baking activation strategy provides a simple route to prepare high-strength, water-resistant starch adhesives for plywood applications.