The effect of mechanical treatment on kraft pulps produced from different softwood raw materials

Fiber deformation is generally considered to be changes in the three-dimensional form of the fiber and fiber damage is considered to be changes in the strength properties of the fiber and fiber network. Usually, fiber deformation and fiber damage occur simultaneously and together are referred to as fiber damage. In this study fiber damage occurring in pulps made from pine and spruce round wood and sawmill chip raw materials were examined in the laboratory. Damage was carried out in the laboratory by mixing the pulp at the end of the cook (170 degrees C) for 15 minutes. The curl index, kink index, fiber length and strength properties were measured for unbleached pulps made from these raw materials as a function of PFI beating. The damaged spruce pulps had lower wet zero-span tensile strength than the damaged pine pulps, although the strengths of the undamaged pulps were at the same level. Furthermore, this study showed that spruce fibers were more deformed than pine fibers under the same mechanical treatment conditions. The results also showed that the tensile index of unbeaten fibers was a good indication of fiber deformation. The curl of the deformed fibers decreased during PFI-beating whereas the curl of the undeformed fibers increased.