Influence of Fiber Alignment on Stiffness and Dimensional Stability of High-Density Dry-Formed Hardboard

The effects of aligning fibers and of their placement within the fiber mat on strength, elastic modulus, and dimensional stability of high-density dry-formed hardboard were investigated. This approach was taken to produce hardboards with increased strength for use as structural components. Four sets of oriented fiber configurations and one set of random-formed control boards 3/16-inch thick were prepared from aspen and from Douglas-fir. For a given species, homogeneous, highly oriented fiber boards showed the great est improvement in strength, elastic modulus, and in dimensional stability. These properties varied in direct proportion to the percent of the total fibers in the one direction. Some loss in cross-direction strength and in stability accompanied these fiber-direction improvements. With the highly oriented boards, the elastic modulus was in the range of that of many clear lumber species. The linear movement in the, fiber direction was also comparable to that for wood in the grain direction. The bending strength and stiffness were the only properties that benefited significantly from concentrating the oriented fibers on the surface of the mat. Tensile strength and both tensile modulus of elasticity and bending modulus of elasticity were improved by orienting alternate layers of fibers perpendicular to the preceding layer but not to the extent of the other oriented boards. The dimensional stability, however, was comparable to that for random-formed control boards in either fiber or cross-fiber direction.

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