Pressing of wood composite panels at moderate temperature and high moisture content

Aspen flakeboards were pressed at 210?F and 25 percent MC using diphenylmethane diisocyanate (MDI) adhesive catalyzed with a tertiary amine. Three adhesive levels (3.0, 5.5, and 8.0 percent), three pressures (press closing times) (400, 500, and 600 psi), and two catalyst levels (0.25% and 0.50%) were used. Press time was 9.5 to 10.5 minutes. A control group of panels was pressed at 350?F, 7.0 percent MC, and 3.0 percent MDI adhesive for 5 minutes. At the 3.0 percent resin level, the high moisture, moderate temperature panels compared favorably to the control panels in flexural apparent modulus of elasticity (MOE) and thickness stability, but the modulus of rupture (MOR) and internal bond strength (IB) were less than that of the control group. The IB, MOR, and thickness stability of the high moisture, moderate temperature panels improved with increasing adhesive level. The high moisture, moderate temperature panels exhibited a more uniform vertical density profile than did the control panels, but more work is necessary to determine whether the novel pressing conditions reduce internal stresses and improve dimensional stability.

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