The characteristics of single stage TMP shives and fibres produced with energy applications in the range 300 to 2000kWh/odt were investigated for both radiata pine thinnings and top logs. Both wood types were found to exhibit a two-stage response as the refining energy was increased. When the applied energy was increased from 300 to 900 kWh/odt the following trends were identified: 1. The whole pulp freeness and fibre length decreased gradually and the shive content reduced rapidly; 2. The lumen perimeter of the liberated fibre increased in a linear manner with a corresponding decrease in the lumen perimeter of the fibres remaining within the shives. In contrast, increasing the applied energy from 900 to 2000 kWh/odt caused: 1. The whole pulp freeness and fibre length to reduce rapidly whereas the shive content which had reached a relatively low level only decreased gradually; 2. The lumen perimeter of the liberated fibre to decrease with no substantial change to the lumen perimeter of the fibres remaining in the shives. The lumen perimeter data indicates that during the initial stages of defibration, the smaller perimeter, thicker walled fibres are liberated from the wood matrix first, with the larger perimeter and thinner-walled earlywood fibres remaining longer in the shive fraction. This finding is used to propose a new processing concept that could enable these two contrasting fibre types to be refined more effectively.
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