Segregation of Aspen, Balsam, and Spruce Wood and Bark Chips Based on Density Differences

The in situ densities of 3/8 inch to 5/8 inch wood and bark chips of quaking aspen (Populus tremuloides), balsam fir (Abies balsamea), white spruce (Picea glauca), sugar maple (Acer saccharum), jack pine (Pinus banksiana), and red pine (Pinus resinosa) were determined as a function of moisture content. A density gradient column was used to measure densities of chips that were oven-dried and then soaked in water for varying periods of time. At equal moisture contents the densities of the bark chips of quaking aspen, balsam fir, and white spruce were greater than those of the corresponding wood chips. The densities of the wood and bark chips of sugar maple, jack pine, and red pine at equal moisture contents were found to overlap quite significantly. In all cases, the bark absorbed moisture at a faster rate than the wood but then leveled off (after an average of 33 hours) whereas the wood continued to absorb moisture over the two week time period studied. Two segregation methods were examined for quaking aspen, balsam fir, and white spruce. 1) A water float-sink process of as-cut, air-dried, and ovendried wood and bark chips showed poor segregation because most of the chips floated, 2) a water float-sink-soaking process revealed as high as 98 percent bark sinking with no wood sinking for ovendried balsam fir. Seventy to 80 percent of the air-dried bark sank before more than 2 or 3 percent of the wood sank for all species.

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