Modified plywood binder preparation process: The effect of urea formaldehyde mole ratio

Abstract

The paper highlights the importance of reducing formaldehyde emissions in plywood products due to increasing public health awareness. Lowering the formaldehyde to urea mole ratio (F/U) during UF resin preparation is a crucial step in achieving this goal. The study focuses on synthesizing UF resin through alkaline-acid process modification involving a strong acid step at the initial stage with a target viscosity range of 120 140 cP. Different F/U ratios were investigated at various condensation steps, with final molar ratios ranging from 1.5 to 1.0. Results indicate that adjusting the F/U ratio during the fourth condensation step (F/U4) is essential to meet desired viscosity requirements. Lower F/U4 ratios lead to decreased reactivity and reduced free formaldehyde content. Resin aging resulted in increased viscosity and gel time, but all resins remained suitable for application for up to three weeks after preparation. Application tests revealed that UF resin with lower F/U4 ratios produced plywood with reduced internal bonding (IB) strength and formaldehyde emissions. F/U4 = 1.1 was found to be the lowest acceptable molar ratio, with formaldehyde emissions of approximately 2 mg/L. These findings stress the importance of optimizing the UF resin synthesis process to achieve lower formaldehyde emission plywood products.