Intrinsically mold-resistant and formaldehyde-free oxidized camellia meal-based adhesive for wood-based panels with excellent water resistance

The development of bio-based wood adhesives exhibiting robust bonding performance, excellent water resistance, and long-term mold resistance is critical for the sustainable manufacturing of wood-based panels. In this work, a formaldehyde-free adhesive was developed by crosslinking oxidized camellia meal (OCM), a non-edible agricultural residue, with hyperbranched polyurea (HBPU). Spectroscopic and structural analyses supported the formation of a crosslinked network involving imine and amide linkages and hydrogen-bonding interactions, which improved the hydrolytic and thermal stability of the cured adhesive. At an HBPU loading of 20 wt%, the OCM–HBPU adhesive achieved shear strengths of 1.22 MPa under dry conditions, 1.15 MPa after immersion in water at 63 °C, and 1.14 MPa after boiling-water treatment. Particleboards bonded with the optimized adhesive exhibited an internal bond strength of 1.70 MPa, a modulus of rupture of 22.22 MPa, and a modulus of elasticity of 3232.60 MPa. No visible mold growth was observed on the adhesive samples over 60 days at 30 °C and 95% relative humidity without added synthetic biocides. A preliminary 21-day soil-based assay showed no obvious inhibition of mung bean germination or seedling growth under the tested conditions. These results support the potential of OCM–HBPU as a formaldehyde-free, water-resistant, and mold-resistant adhesive for wood-based panels.