Birch chips, treated with bisulfite at various yield (70-90%), were fiberized in the Asplund Laboratory Defibrator D (as the first refining) and refined in the PFI mill (as the second refining) to produce CTMP.
The effects of pretreatment yields and refining temperatures on the fiber length distributions and fiber surface structures of CTMP were discussed. In addition, the relationships between morphlogical properties of the fines and the sheet strength properties were discussed.
At the yield of pretreated chips less than 84%, the fiber wall of the pretreated chips were ruptured between the primary wall and the middle lamella on the fiberizing stage, and then the fibers were seperated without damaging. The fines generated on this stage consisted of the ray cell and the flake-like fragments which were derived from the middle lamella and the primary wall layer.
At the yield of pretreated chips more than 90%, the pretreated chips were fiberized in a similar manner descrived above. However, the presence of fragments derived from the cell wall was found in the fines fraction.
In the case of various yields, there is no significant differences in the long fiber (> 48 mesh) contents of the pulps produced on the fiberizing stage.
When the defibration temperture decreased from 130°C to 100°C or 20°C, the fibers were significantly damaged during the fiber seperation, and the contents of the long fiber decreased.
Fiber surface structures and the fiber length distributions showed that the fibers produced from the pretreated chips with a yield of 93% were subjected to destruction on the refining stage, and decreased the long fiber contents. The fines generated on this stage contained more fiber wall fragments.
This tendency was reduced with decrease of the pretreatment yield, and a larger portion of the fines consisted of the fillament-like fragments which were derived from the secondary wall by peeling from the fiber surface.
The fines generated on the fiberizing stage were less effective to the sheet strength properties. On the other hand, the fines generated on the refining stage consisted of the fillament-like fragments which derived from the secondary wall, and were more effective to the inter fiber bonding.
