No abstract

An air-injection press was developed to prevent particleboard from blowing out during the manufacturing process. The air-injection press, which has holes punched in the heating plates, injects high-pressure air into the board through the holes of one plate and releases the air through the holes of the other plate. The high-pressure air forces out vapor trapped within the board, thus preventing blowout. The newly developed press reduced the pressing time required for manufacturing board from high-moisturecontent particles. However, the manufactured boards exhibited mechanical properties and dimensional stability inferior to conventionally manufactured boards.

Fiberboards were prepared from acetylated fibers with various weight gains: 0, 4.7, 9.4, 18.5, and 24.8 weight percent gain (WPG). The effects of low bondability of acetylated fibers on mechanical properties and dimensional changes were determined. The decreased mechanical properties of acetylated fiberboard are mainly due to low bondability. To improve bending strength, high face density is also needed. The thickness swelling according to JIS and the linear expansion under relative humidity changes decreased with increasing WPG. As for accelerated weathering and the outdoor exposure test, the thickness changes in 4.7-18.5WPG boards were much higher than those in 0WPG board and 24.8WPG board. The high thickness change in 4.7-18.5 WPG boards is due to low'bondability. Although 24.8WPG board also has low bondability, the thickness change of 24.SWPG board decreased. The high dimensional stability of acetylated fibers, caused by high WPG, probably outweighs the dimensional change caused by low bondability. On the other hand, during the boiling test the thickness changes in 24.8WPG board and the 4.7-18.5WPG boards were higher than those in 0WPG board. The effect of the boiling test on the boards is more severe than that seen with the accelerated weathering and outdoor exposure test; therefore, the effects of the low bondability probably cancel the effects of the high WPG. It is necessary to increase the bondability of acetylated fibers to improve the dimensional stability and the mechanical properties.

No abstract

Wood-based boards were exposed to an outdoor environment at angles of 90° and 45° to the ground surface in order to investigate the effect of exposure angle on board properties. In a study on 5-year outdoor exposure, the effects of the exposure angle varied depending on the type of board. Particleboard (PB) and oriented strand board (OSB) deteriorated faster when exposed at 45° compared with 90°, and the difference was more apparent with longer exposure. Five years of exposure at 45° lowered the retention of the modulus of rupture and internal bond of phenolic resin–bonded PB to 15 and 4 percent, respectively. In contrast, medium-density fiberboard (MDF) showed no difference in deterioration between both exposure angles. After 5 years of exposure, the retention of the modulus of rupture was 70 to 80 percent in MDF, while that of internal bond was 81 to 97 percent, thereby showing that the internal bond was better retained than the modulus of rupture. The high durability of MDF was attributable partly to its smoother surface compared with the other boards, which prevented residual rainwater on the surface from infiltrating into the board. Conversely, PB and OSB were prone to surface weathering, which led to the ingress of rainwater. The resultant swelling resulted in the collapse of bonding points, followed by the formation of voids inside the boards. Residual moisture in the voids then caused decay as well as a further reduction in strength (biodegradation).