Flakeboard Thickness Swelling. Part II. Fundamental Response of Board Properties to Steam Injection Pressing
Keywords:Flakeboard, steam injection, bending, shear, thickness swelling
AbstractThe results of this study showed that the same relative reductions in thickness swelling (TS) previously obtained with steam-injection-pressed (SIP) resinless mats are also obtained in boards bonded with 3% isocyanate resin. Reductions in thickness swelling were proportional to steam time and pressure. Thickness swelling of 40% measured in conventionally pressed boards following a vacuum-pressure-soak treatment was reduced to 25% in a board exposed to 20 sec of steam at 600 kPa and to 6% in a board exposed to 40 sec of steam at 1,900 kPa. We believe that the reductions in thickness swelling result from a combination of flake plasticization, "lignin flow," and chemical modification. Bending properties of the SIP boards were substantially lower than that of conventionally pressed boards, which we attribute in part to the very short press times and the relatively fast decompression used to manufacture the SIP boards. Bending properties of SIP boards also suffered from a reduction of the vertical density gradient. However, this characteristic is favorable to shear properties.
ASTM. 1992. Standard methods of evaluating the properties of wood-based fiber and particle panel materials. ASTM D 1037-92. American Society for Testing and Materials, Philadelphia, PAnGeimer, R. L., J. H. Kwon, and J. Bolton. 1988. Flake-board thickness swelling. I. Stress relaxation in a flake-board mat. Wood Fiber Sci. 30(4): 326-338.n
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