Durability of Medium Density Fiberboard Subjected to Outdoor Exposure

MDI-bonded MDF (MDF(MDI)) and phenol formaldehyde resin bonded particleboard (PB(PF)) were subject to outdoor exposure to investigate their durability. The retention of modulus of rupture, internal bond, nail-head pull-through, and lateral nail resistance of PB(PF) was 46.5, 16.9, 60.9, and 28.0%, respectively, and for MDF(MDI) was 77.1, 96.7, 86.4, and 87.8%, respectively, during a five-year outdoor exposure test at Tsukuba. For the same tests at Miyakonojo. the retention of modulus of rupture, internal bond strength, nail-head pull-through, and lateral nail resistance of PB(PF) was 24.1, 6.73, 52.5, and 22.6%, respectively, and for MDF(MDI) was 75.1, 100, 87.9, and 66.8%, respectively. All retentions of PB(PF) at Miyakonojo, subject to high temperature and precipitation. exceeded those at Tsukuba, but there were no differences between MDF(MDI) at Tsukuba and Miyakonojo. The high durability of MDF was attributable to its smoother surface compared to PB(PF), which prevented rainwater from remaining on the surface and infiltrating into the board due to fiber intertwining.