Hydrolytic Removal of Cured Urea–Formaldehyde Resins in Medium-Density Fiberboard for Recycling

This study focused on the removal of cured urea–formaldehyde (UF) resins by hydrolysis of medium-density fiberboard (MDF) at different temperatures and times for MDF recycling. Five aqueous solutions, i.e., two acids, two alkalis, and water, were used for MDF hydrolysis to obtain extract solutions and solid residues for the analysis of mass balance, nitrogen content, and resin removal. As expected, acidic solutions removed the greatest amount of cured resins, followed by water and alkaline. Moreover, temperature had a greater impact on hydrolysis than time. Fourier transform infrared spectra of MDF fibers before and after hydrolysis clearly showed the change in intensity of the amide group in UF resins. Reduction of the amide group was greater with increase in hydrolysis temperature than in time. Statistical analysis results suggested that the hydrolysis of MDF at 80°C for 2 h using oxalic acid solution was optimum condition for the removal of cured UF resins. However, water could be used as hydrolysis agent for the practice of MDF hydrolysis in the future.