Bending strength and internal bond strength of wood-based boards subjected to various exposure conditions

Abstract

Phenol–formaldehyde resin-bonded particleboard (PF board), methylene diphenyl diisocyanate resin-bonded particleboard (MDI board), aspen oriented strand board (aspen board), Scots pine oriented strand board (pine board), methylene diphenyl diisocyanate resin-bonded medium-density fiberboard (F-MDI board), and melamine–urea–formaldehyde resin-bonded medium-density fiberboard (F-MUF board)—six board types overall—were subjected to high relative humidity (90 %, 20 °C) or cyclic humidity of high/low relative humidity (90/45 %, 20 °C) for 5 years. The PF board and aspen board showed reduction in bending strength [modulus of rupture (MOR)] and internal bond strength (IB); however, the MDI board, pine board, F-MDI board, and F-MUF board showed almost no reduction. Furthermore, the boards were subjected to outdoor exposure and Test B (boiling for 2 h) from the Japanese Industrial Standard (JIS); the results showed large reduction in the MOR and IB of the PF board and aspen board. In contrast, outdoor exposure did not greatly reduce the MOR and IB of the F-MUF board and F-MDI board. Although the IB of the F-MUF board reduced after the JIS Test B because of using low-durability resin, the IB retention was as high as 87.8 % for 5-year outdoor exposure.