Effects of water soaking and outdoor exposure on modulus of rupture and internal bond strength of particleboard

Phenol–formaldehyde resin-bonded particleboard (PF board) and isocyanate resin-bonded particleboard (MDI board) were soaked in water at 40, 70 and 100 °C, and the relationships between soaking conditions and board properties were analyzed. The relationships between the deterioration of board properties resulting from water soaking and those arising from outdoor exposure were also analyzed. At 100 °C, the modulus of rupture (MOR) and internal bond strength (IB) of the PF board decreased significantly within the first hour, and subsequently constant values were shown with increasing soaking time. This low constant value was defined as the lower limit. At 70 °C, both the MOR and IB decreased with increasing soaking time, and reached the lower limit. At 40 °C, however, neither decreased significantly with increasing soaking time and neither reached the lower limit. The MOR of the MDI board showed the same trend as the PF board. However, the IB of the MDI board showed a different trend to the PF board, that is, the lower limit of IB required extensive soaking, even at 100 °C. The MOR and IB of both the PF and MDI boards reached the lower limit when thickness change peaked. On the other hand, the MOR and IB for outdoor exposure were lower than those for water soaking, even at the same thickness change. The MOR and IB of water soaking decreased owing to the collapse of the bonding points caused by board swelling. On the other hand, the board properties of outdoor exposure decreased owing to the collapse of the bonding points, and biodegradation also added to the decrease.