Manual strand orientation as a means of improving the flexural properties of wood-wool cement boards in the Philippines

In the Philippines, wood-wool cement boards (WWCBs) are manufactured from plantation hardwoods in labor-intensive, small-to-medium scale plants. In the majority of these plants, cement-coated wood-wool (excelsior) strands are randomly formed into mats by hand (prior to pressing), which gives an opportunity for much greater control of the mat forming process than is possible in fully-automated plants. Since improvements to the mechanical properties of wood composites can be achieved by aligning their particulate constituents, it is possible that a similar effect could be achieved by orienting wood-wool strands within WWCBs. The aim of this study was to determine the feasibility of manufacturing WWCBs containing hand-oriented wood-wool strands and the improvements (if any) in board properties resulting from strand orientation. The flexural strength properties (modulus of rupture and modulus of elasticity) of WWCBs with a cross-ply orientation, in which surface strands were oriented parallel to the long axis of test specimens, were twice those of the randomly oriented control. Improvements in strength properties were comparable to those that can be achieved by aligning flakes in flakeboards. When the surface strands of cross-ply specimens were oriented perpendicular to the long axis of test specimens, modulus of elasticity was lower than that of the control. The nailhead pull-through strength of WWCBs was not affected by orientation of strands in the boards. It took three times as long, however, to prepare hand-formed oriented wood-wool mats compared to preparing mats in which strands were randomly oriented. Nevertheless, hand-forming of wood-wool strands to produce WWCBs with a 3-layer cross-ply structure shows promise as a means of improving the flexural properties of WWCBs manufactured in the Philippines.

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