Phenol-Glyoxal Precondensate Crosslinked Soy Protein Adhesive and Its Plywood Manufacturing Process

Abstract

To develop high-performance soy protein-based adhesives, this study employed a phenol-glyoxal precondensate as a crosslinking agent and optimized the hot-pressing process parameters for plywood through orthogonal experiments, exploring its feasibility for application in wood-based panel manufacturing. Electrospray ionization mass spectrometry (ESI-MS) and nuclear magnetic resonance (¹³C-NMR) analyses revealed the self-polymerization behavior of glyoxal and its condensation reaction pathway with phenol under acidic conditions, confirming that cyclic ether intermediates were predominant. Using boiling water-resistant bond strength as the evaluation index, orthogonal experiments were conducted to optimize hot-pressing temperature, pressure, time, and glue spread amount. The results demonstrated that hot-pressing temperature exerted the greatest influence on performance, with the optimal conditions being 170 °C, 1.4 MPa, 1.0 min/mm, and 330 g/m². The crosslinking agent enhanced the compactness and water resistance of the adhesive layer through multi-site covalent bonding, hydrogen bond entanglement, and π-π stacking, providing a reference for the industrial application of bio-based adhesives.