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Figure5. Comparison of freeness drop rate of SwBKP and HwBKP during beating and refining.
In contrast, the beating curve for HwBKP shows a noticeable plateau after approxi- mately 40 min, where the rate of freeness reduction slows significantly. This plateau can be attributed to the gradual exhaustion of readily accessible fiber surfaces for fibrillation and swelling, meaning that further mechanical action produces diminishing changes in pulp drainage characteristics. As beating continues, additional treatment has a limited effect on freeness due to the increased resistance of more fully fibrillated and shortened fibers, which is a typical feature seen with hardwood pulps under prolonged beating conditions. The disk refiner, particularly when fitted with ultra-fine bar patterns, applies highly controlled and intense mechanical action to the pulp fibers. As shown in Figure 6, its consis- tent bar and groove dimensions, along with uniform gap clearance, enhance the frequency and effectiveness of fiber-bar interactions [24]. This design maximizes the contact surface area and increases the number of bar impacts per unit time, thereby promoting both internal and external fibrillation of fibers, which is critical for rapid freeness reduction [25–27].
Figure6. Schematic diagram of the refining mechanism using a disk refiner.
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