Effects of urea–formaldehyde resin mole ratio on the properties of particleboard

The use of urea–formaldehyde (UF) resins with lower contents of free formaldehyde in the board industry has led to products with very low emissions of formaldehyde. This study gives a detailed account of the influence on the mechanical and physical properties of the particleboard using UF resins with different mole ratios of formaldehyde:urea within the range 0.97–1.27. The mole ratio influenced not only the thickness swelling (TS) and water absorption (WA) but also the internal bond strength (IB) and the modulus of rupture (MOR) if the manufacturing process was optimized. The investigation revealed clearly that at mole ratios of formaldehyde giving the emission class El the MOR, IB, TS, and WA of particleboard deteriorated. Compensation for the deterioration could be provided through a higher dosage of resin or through the modification of UF resin. However, both alternatives meant that the product would be more expensive.