Impacts of urea-formaldehyde resin residue on recycling and reconstitution of wood-based panels

Recycling and reuse of wood-based panels has been attracting great attention since it is an environmentally friendly means of managing wood waste. The recycled wood-based panels usually still contain adhesive residue. In the current research, the impact of urea-formaldehyde (UF) resin, one of the most widely used adhesives, on recycling and reconstitution of wood-based products has been evaluated by adding cured UF resin particles into a new adhesive system. The morphology, chemical structure, curing behavior, and bonding quality of an adhesive system containing 0–6% previously cured resin particles of varied sizes (< 600 μm) were investigated and compared to those properties of a regular adhesive without any impurity. Three-ply plywood glued with a UF adhesive containing 0–10 wt% previously cured resin of varied particle sizes (< 600 μm) were prepared and characterized. The results indicated that the resin residue could significantly affect the curing behavior and bonding quality of the new adhesive system. Higher content and greater size of the particles caused more severe deterioration in the bonding strength.