Eco-Friendly Phenol–Urea–Formaldehyde Co-condensed Resin Adhesives Accelerated by Resorcinol for Plywood Manufacturing

[Image: see text] Eco-friendly and good-performance resin adhesives are needed for wood manufacturing. In this study, phenol–urea–formaldehyde (PUF) resin adhesives were modified by adding various ratios of resorcinol. The properties of PUF, phenol–resorcinol–urea–formaldehyde (PRUF) resin adhesives, and the performances of the prepared plywood were tested. The curing behaviors and the structural features of the PUF and PRUF resin adhesives were investigated via dynamic scanning calorimetry, thermal gravimetric analysis, (13)C NMR, and cross polarization magic angle spinning (13)C NMR. The results indicated that 1.3% resorcinol (based on resin, w/w) could decrease the curing temperature and accelerate the curing process after PUF resin modification. The PRUF resin adhesives demonstrated a lower activation energy during the curing process, with up to 28.8% less energy than that of PUF resin adhesive without any curing agent. The plywood demonstrated low formaldehyde emissions (<0.1 mg L(–1)) and acceptably high bonding strengths (>1.00 MPa). This work provided a method for preparing an easy-cured and high-performance phenolic resin for wood manufacturing.