Resin Treatments for Improving Dimensional Stability of Structural Fiberboard

Hardboards were made more stable by adding a small amount of water-soluble phenolic resin to the surfaces of the wet mat. Thickness stability and bending strength were increased. This type of treatment is attractive because not only is the resin placed where it is most effective, but more of the resin is retained by the board thereby reducing the possibility of resin pollution–a problem that occurs when chemicals are added to pulp furnishes. Additions of powdered phenolic resin to the pulp furnish were also effective in reducing both the linear and thickness movements. Both of these properties were improved with increasing amounts of resin. A powdered hydrocarbon resin was not so effective as the phenolic resins. All experimental hardboards were formed in a defibrator freeness tester and mat former that produces an 8-3/4-inch diameter board. High-density hardboards 1/4-inch thick and medium-density hardboard 3/8-inch thick, both screen back, were made from balsam fir and aspen pulps. Medium-density hardboards, 1/2-inch thick, smooth two side, were made from balsam fir refiner groundwood pulp with either a powdered phenolic resin or a powdered hydrocarbon resin added to the pulp slurry.

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