ETD

• eucalyptus fibers
• morphological analysis
• recirculating refining system
• refining
• strength indices

In recent years, tissue paper manufacturers have faced a significant increase in the cost of their main raw material, namely cellulose pulp, driven by economic, geopolitical, and logistical factors. In this context, the persistent price gap between long-fiber pulp (NBKP), more expensive, and short-fiber eucalyptus pulp (BEKP) has encouraged producers to explore alternative solutions aimed at reducing raw material costs while maintaining the required performance of the final product.
One potential strategy involves the use of a refining system with recirculation applied to short eucalyptus fibers, which is capable of producing highly flexible, extensively fibrillated fibers with a high content of secondary fines. These characteristics enhance inter-fiber bonding and partially compensate for the structural role typically provided by long fibers.
The objective of this thesis is to analyze, from both a morphological standpoint and in terms of strength indices, four different eucalyptus pulps subjected to a refining system with recirculation, comparing their behavior with each other and assessing the overall process runnability. The strength properties developed by these short-fiber pulps are also compared with those obtained from long-fiber pulps.
Experimental trials were carried out at the Sofidel plant in Valdottavo. Morphological analysis showed that eucalyptus fibers treated with recirculating refining exhibit a lower average fiber length compared to conventionally refined long fibers, while displaying a significantly higher content of secondary fines and markedly enhanced fibrillation parameters. These features lead to a substantial increase in the relative bonded area (RBA), which in turn results in strength properties comparable to those achieved with a conventional refining system, in which long fibers account for 30% of the total furnish, compared to 19% in the recirculation system. This highlights a substantial reduction in long-fiber usage without compromising process runnability or final product performance, demonstrating the feasibility of significantly reducing raw material costs.