Oxalic Acid Hydrolysis as a Recycling Route for Laminated Particleboards: Properties and Formaldehyde Emissions of New Panels

The growing global demand for particleboards has generated large quantities of waste in recent years. This waste mainly arises from manufacturing processes, furniture industry offcuts, and end-of-life disposal. In response to waste management challenges, recycling and reuse technologies have advanced significantly. In this context, this study evaluates the feasibility of producing new particleboards using recycled particles obtained from laminated particleboard waste. Recycled particles were treated with hot water, oxalic acid, and a combination of both, and the most effective treatment was selected for panel production. Hot water treatment was insufficient to remove the cured UF resin and promote particle separation, whereas oxalic acid successfully achieved both. Three-layer panels were then manufactured using oxalic acid-treated recycled particles at incorporation levels of 0%, 25%, 50%, 75%, and 100% in the core layer. The average density, vertical density profile, and physical and mechanical properties, as well as the formaldehyde emissions, were assessed. The results showed that the inclusion of recycled particles did not significantly impact the average density or the vertical density profiles of the panels. Thickness swelling and water absorption after 24 h immersion were similar across all panels, indicating good dimensional stability. Internal bond (IB) strength showed no consistent trend with increasing recycled particle content, and panels with 75% recycled particles achieved the highest IB strength (0.48 MPa). In contrast, bending properties decreased when the proportion of recycled particles exceeded 25%. All panels satisfied the requirements of the LD-2 Grade for low-density particleboards specified by the ANSI A208.1-2022 standard. An increase in formaldehyde emissions was observed in panels containing more than 25% recycled particles compared to the control panels. These findings indicate that particleboards can incorporate up to 75% recycled particles in the core, while maintaining physical and mechanical properties comparable to those of the control panels.