Measurement of the bark/wood shear strength: practical methods to evaluate debarking resistance of Norway spruce and Scots pine pulpwood

The purpose of this study was to describe how the ability to debark can change due to log storage and to explore a practical method to measure the freshness of pulpwood when it is delivered with respect to its debarking resistance. Bark in pulp is undesirable because it increases the need to use chemicals for cooking and bleaching. Dry pulpwood increases energy consumption and wood loss when debarking, chipping, and refining. The bark/wood shear strength of 40 spruce and 40 pine pulpwood piles at 4 pulpmills in Sweden was studied. The pile, measured 10 m3 and were evaluated over a 14- or 15-week storage period. The bark/wood shear strength did not change appreciably during the first 6 weeks of storage. After 6 weeks, an obvious increase in the shear strength was observed. Both bark/wood shear strength and green density were correlated (r2 = 0.75) with the moisture content of the sapwood. The variation within and between logs was high. Norway spruce had a higher shear strength than Scots pine. The models tested show relatively good promise for finding extremes (wood piles with a high shear strength), which can lead to unsatisfactory debarking.

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