Internal Bond and Moisture Response Properties of Three-Layer, Wood-Bark Boards

Recent antipollution legislation has resulted in mounting pressure on the forest products industry to seek uses for material such as bark, previously regarded as a waste material. In this study, a variety of three-layer composite boards were made by using two bark species for the core, and varying the pressing conditions. The surfaces of the boards consist of western white pine (Pinus monticola) wood flakes, which enclose bark-particle cores of either Douglas-fir (Pseudotsuga menziesii) or grand fir (Abies grandis). The bonding resin content by weight of the surfaces was 5 percent, and that of the bark ranged from 6 to 10 percent. Determinations were made of those properties which were expected to be strongly influenced by the presence of the bark cores, namely IB, water absorption, and linear expansion. The IB values increased substantially with increase in resin content, and the grand fir gave much higher values than did the Douglas-fir. Water absorption characteristics were reasonably close to those of wood particleboard. Linear expansion was excellent. Further development and improvement of the composite boards would provide the forest products industry with a bark product of value, usable for structural applications such as roof panel and subflooring. Adoption of the product would alleviate, in part, the pollution problems associated with many current methods of bark disposal.

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