LOW ENERGY SHIVE SEPARATION EVALUATION OF A NEW METHOD OF FIBRE PROCESSING

摘要

The potential of a new mechanical pulping strategy to enable the separate development of earlywood and latewood fibres has been evaluated in a pilot plant study. In this study, wood chips were treated with a low energy application to produce a primary-stage pulp containing a high proportion of shives. Conventional "fractionation technologies" were then used to separate the shives from the liberated fibres so that these two streams could be given separate refining treatments. The key observations from this study were; 1. Fractionating a low energy feed pulp containing 57% shives is difficult as this type of pulp dewaters and thickens very quickly resulting in blocked pipes and valves. However, processing the pulp at 0.5% consistency produces an accept pulp containing 5 % shives and rejects with 73 % shives. 2. Pressure screens are more "efficient" in removing shives from the single stage pulp than hydrocyclones. 3. The fibre dimension data obtained from the screening stage provided support for this processing concept where earlywood and latewood fibres are separated as the shives (rejected by the screening system). The shives contained fibres with an average lumen perimeter of 88 μm, and the liberated fibres (accepted by the screens) had an average lumen perimeter of 80 μm. 4. The differences in fibre length and fibre lumen perimeter observed after fractionation were maintained when the liberated fibre (accepts) and shives (rejects) were given additional refining treatment. The fibres from the refined shives consolidated to the same sheet density, but had higher tensile strength than the fibres from the refined liberated fibre. This indicates that the earlywood fibre in the refined shives may be more fibrillated or have greater surface development than the latewood fibre in the refined liberated fibre stream. These findings indicate that this new process strategy can enable more effective treatment of fibre types based on their dimensions, and increase the ability to direct a given fibre type to the most appropriate end use.