The effect of modified paraffin on the bonding performance of urea-formaldehyde adhesive

Wood-based panels bonded with urea-formaldehyde (UF) adhesive serve for construction and furniture manufacturing with excellent physical properties and cost-effectiveness. However, the moisture susceptibility of wood limits its applications and service life. The paraffin emulsions can provide waterproofing, whereas excessive paraffin weakens the bonding strength of wood-based panels. In this study, the modified paraffin with superior dispersion was prepared and the accompanying effects on the bonding performance was investigated. Results indicated that the modified paraffin emulsion with a mean particle size of 3.17 μm, which decreased by about 84.6% as compared to the commonly used paraffin. FTIR, XPS, SEM, and contact angle measurements showed that the modified paraffin reduced hydrophilic groups and enhanced the hydrophobicity. The commonly used paraffin particles are prone to agglomerate, which reducing the adhesive penetration depth of UF adhesive into wood. After modification, the penetration depth of UF adhesive into wood was increased by about 52.3%. The improved permeability of UF adhesive into wood contributed the highest tensile shear strength of glued wood with modified paraffin under both dry and wet conditions. Shear strain distribution during the test indicated that the modified paraffin enhanced stress transfer capacity within the glueline, improving mechanical performance. These findings are beneficial to develop the wood-based panels with high bonding performance and moisture-resistance for outdoor applications.