Appl. Sci. 2025 , 15 , 9160
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Figure3. ( a ) Single disk refiner; ( b ) Lightweight plate for low-intensity refining.
Figure4. Bar dimensions of the lightweight plate for ultra-low intensity refining.
2.3. Analysis of Pulp and Paper Properties The mean fiber length of pulp fibers was measured using the Fiber Quality Analyzer FQA-360 (Optest Equipment Inc., Hawkesbury, ON, Canada). For assessing the physical properties of paper, handsheets of 70 g/m 2 were prepared, conditioned, and tested follow- ing ISO 5269-1 [22]. The physical properties, specifically tensile, burst, and tear strength, were measured by ISO 5270 [23]. Microscopic observations of fiber morphology and structural changes were conducted using an Olympus BX51 optical microscope (BX51, OLYMPUS, Tokyo, Japan). Samples of softwood and hardwood bleached kraft pulps before and after mechanical treatment were prepared by placing diluted pulp suspensions on glass slides and observed under magnifications of 100 × and 200 × . The imaging allowed qualitative assessment of fiber length, fibrillation, and surface characteristics to clarify the effects of Valley beating and ultra-fine bar refining on fiber structure.
3. Results 3.1. Freeness
Figure 5 compares the freeness drop rate of pulp stocks during beating and refining. The results show that the refiner plate with the ultra-fine bar pattern induced a much faster reduction in freeness for both SwBKP and HwBKP compared to beating. This efficiency arises from several factors inherent to the refiner design: the disk refiner achieves highly controlled, intense fiber treatment due to its consistent bar and groove pattern and uniform gap clearance, maximizing the frequency and effectiveness of fiber-bar interactions. This promotes both internal and external fibrillation and enables rapid freeness reduction.
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