Hardwood Bark Properties Important to the Manufacture of Fiber Products

Bark properties believed to be important particularly to the paper industry include inner and outer bark morphology, specific gravity, extractives, fibrous yield, wood/bark adhesion, bark strength, bark toughness, reaction to hammer-milling, water flotation behavior, fuel value, and ash content. Examples of data generated are presented for five species of hardwoods. Large differences were found between species in morphology, chemistry, and mechanical properties of the bark. Average growing season wood/bark adhesion was similar for all species (3-6 kg/cm ) and observations made on the failure zone demonstrated failure quite consistently occurred in the cambium zone or the newly formed xylem elements just inside the cambium. Dormant season wood/bark adhesion varied considerably between species and was higher than during the growing season. Failure usually occurred in the inner bark relatively close to the cambium zone. Extremely high dormant season adhesion appeared to be associated with the presence of large numbers of fibers in the inner bark. Bark extractives levels varied from 5 to 17 percent, levels of usable kraft fiber from 0 to 10 percent, and the estimated amount of bark that could be removed by a combination of mechanical action and screening varied from 29 to 46 percent.

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