High moisture content of the wood. For this, the wood is stored in bundles in

Lakes, sea bays or watering ponds, with the log bundles being moved and turned

Using special boats.

3.2.2

Wood Log Debarking

For further processing, the wood must be debarked. Bark cells are formed outside

The living part of the tree (the cambium), and consist of the phloem (inner bark)

And bark (outer bark). Phloem cells are responsible for the transportation of

Assimilates and storage, while the bark protects the living parts of the wood from

Drying, temperature influences or damage. Depending on the wood type, the

Thickness of the bark layer is between 2 and 40 mm. This corresponds to a bark

portion of 5 to 28%, in relation to the total wood stem.

The different chemical and morphological composition of the bark compared to

That of the wood makes it necessary to remove the bark from the wood before

Mechanical pulping is carried out. Bark particles are responsible for dirty points

In the paper and reduced paper quality. The higher the quality of the paper, the

Raw Materials for Mechanical Pulp

Fewer bark particles should be retained on the wood stems after debarking. In line

With the morphological construction of the bark layer, bark removal should take

Place at the contact area between the phloem and cambium. One measure of characterization

Of the ability to wood be debarked is the debarking resistance or the

Power and force, respectively, per cm2 of bark that is needed to remove the bark

from the wood stem. Debarking resistance is influenced by:

_ Wood type

_ Felling time (season)

_ Moisture content of the wood

_ Storage duration of the wood

_ Temperature in the cambium area

_ Type of pretreatment

For example, debarking resistance is highest for birch, followed by spruce and

Pine, but it also depends very heavily on the felling season of the wood (Fig. 3.1).

Seasonal differences in debarking resistance are also related to the morphological

Differences, depending on growth. During spring and summer, when cell division

Activity is very high, the radial walls of the cambial cells and the neighboring

Phloem cells are very thin and weak, and at this time the debarking resistance is

Low. However, if cell division activity is low or is stopped, and liquid transportation

Though the cells is very restricted, debarking resistance is increased significantly.

Debarking resistance [N/cm * 2.5]

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Fig. 3.1 Seasonal development of debarking resistance.

Transversal resistance; 2, Longitudinal resistance; 3, Tanning limit.

Debarking resistance also increases with decreasing moisture content of the

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