Characterization of fiber development in high- and low-consistency refining of primary mechanical pulp

Abstract

Primary refined softwood was subjected to highconsistency (HC) or low-consistency (LC) secondary refining, and the nature of the development of the internal and external fiber microstructure and ultrastructure has been compared. The primary refining of mixed softwood as a raw material was performed in pilot scale by the advanced thermomechanical pulp process. The study was aiming at the comparative characterization of LC and HC pulps at the fiber level when produced with similar and well-characterized handsheet properties. The formerly described Simons' staining method was applied. A significant degree of fiber wall delamination/internal fibrillation (D/IF) was observed during both LC and HC refining. Both the energy input and the refining consistency had a significant impact on elevating the degree of fiber wall D/IF. The statistical evaluation of internal fiber development indicated that the fiber populations in LC-and HC-refined pulps had a similar degree of fiber wall D/IF despite having a large difference in refining energy input (420 kW h odt -1 ), confirming that D/IF was promoted more energyefficiently in LC than in HC refining. The characteristic of the external fiber development from HC and LC refining was very different. Secondary LC refining promoted fiber surfaces with ribbons of thin hairlike threads arising from the inner secondary S2 layer that occasionally developed along the whole fiber length. Broad sheet-and lamellaetype external fibrillation from the S2 was typical for HC refining, and these characteristics were rarely observed in the LC pulps. The mechanisms for LC and HC fiber development are proposed. The cell wall characteristics (internal and external) of the pulp fibers appear to govern most of the physical and optical properties in handsheets.

Modeling of tensile index using uncertain data sets

“…Moreover, from a physical perspective it is sound to include the dilution water feed rates and consistencies as predictors. The reason is that they are related to changes in fiber distribution in the refining zones (Fernando et al 2013), which certainly affect the final pulp and handsheet properties even if the specific energy is not changed.…”

Low consistency refined ligno-cellulose microfibre: an MFC alternative for high bulk, tear and tensile mechanical pulp papers

“…9 The fibre length distribution of primary TMP shifts gradually to the left with increased refining (a); a comparison of length distribution among the four categories of pulp at interlocking between fibres. This promotes fibre collapse and the formation of rigid fibre networks, creating stronger but denser sheets with low elongation property (Fernando et al 2013;Kang and Paulapuro 2006).…”

“…10b-d. Small area of contact between stiff fibres of the high freeness pulp typically leads to weaker bonding and lower strength properties (Fernando et al 2013;Forgacs 1963). The application of high specific energies through excessive LC refining breaks down fibre constituents and liberate a large number of fines and fibrils during microfibre production.…”

“…The surfaces of handsheets made with the addition of TMP-based microfibres to primary pulp also revealed fibre-fibril interactions, in (b) and (c); however, these microfibres contained large number of ribbon-type fibrils, compared to KMF. The ribbontype fibrils are characteristics of secondary S 2 layers of fibre cell walls (Fernando et al 2013;Forgacs 1963;Hafrén et al 2014). The fibrils in mechanical pulpmicrofibres appear to be more localized, covering relatively smaller number of intact fibres of primary TMP.…”

Improved Bleached Chemical Reed Pulp Properties Using Atmospheric High Consistency Refining

“…Refining chemical pulp with a pulp consistency range of 20 to 35% can increase the internal fibrillation, retention of fiber length, and fiber curl and kink while generating fewer fines (Senger and Ouellet 2002;Gurnagul et al 2009;Ferritsius et al 2012;Fernando et al 2013;Kerekes 2015). Higher fiber length and more internal fibrillation improves the tear strength, while the generation of fewer fines improves the pulp drainage.…”