Some fundamental aspects of mechanical actions on wood pulp fibers have been studied. Specifically, the objectives of the study were to produce internal fibrillation in pulp fibers, evaluate its influence on paper properties, and establish its importance relative to external fibrillation and fines in terms of paper property development.
An apparatus was constructed that subjected pulp fibers (in the form of a wet handsheet) to repeated compressive loading cycles. Pulp was also treated in an experimental apparatus designed to promote external fibrillation, and in a Valley beater. Several fiber and paper properties were measured.
The results showed that internal fibrillation could be produced with the repeated compressive action of the apparatus. The effect of internal fibrillation on paper properties caused a threefold increase in breaking length, from 2 km to 6 km. This level was 75% of the highest breaking length achieved with the Valley beater, which was 8 km. The reason for the difference in breaking length between the samples is due to the (calculated) differences in fiber-fiber bond shear strength. By adding fibrillation to internally fibrillated fibers and forming the sheet, no change in breaking length was achieved. However, adding fines to a suspension of internally fibrillated fibers increased the sheet breaking length, almost to the level produced by Valley beaten fibers.
From these results, it was concluded that internal fibrillation in pulp fibers plays the largest part in improving sheet breaking length. Also, fines are a necessary supplement in the fiber network to improve interfiber bonding. The effect of external fibrillation had no apparent influence on improving breaking length, but its importance may lie elsewhere in the sheet forming process. Internal fibrillation and fines can be produced in separate steps, indicating an additive approach to developing sheet properties through refining is possible.