Appl. Sci. 2025 , 15 , 9036
6of 13
97 km/s. As shown in Figure 3a,b, increasing refining energy leads to a decrease in mean fiber length and an increase in fines content for both plate types. Notably, the ultra-fine bar plate with a CEL of 97 km/s causes a more rapid drop in fiber length and a quicker rise in fines content at lower refining energies compared to the conventional plate. This trend is consistent with the findings of previous research, which reported that plates with sharper bar edges and higher CELs result in more aggressive fiber cutting, especially in the early refining stages [7]. Similar results highlight the amplifying effects of refining intensity and plate design on fiber shortening and fines production in recycled fibers [24].
( a )
( b )
( c )
( d )
Figure 3. Effect of refining energy on mean fiber length and fines contents for KOCCs with different CELs. ( a ) Refining energy versus fiber length. ( b ) Refining energy versus fines contents. ( c ) Freeness versus fiber length. ( d ) Freeness versus fines contents. However, a closer analysis using Figure 3c,d, which relate fiber length and fines content to freeness, reveals a key nuance: at comparable freeness (i.e., when the drainage resistance of the pulp is matched), the mean fiber length and fines content are very similar for both plates. In other words, while the ultra-fine bar plate accelerates fiber modification— achieving target freeness with less total energy input and in fewer refining passes—it does not lead to increased fiber cutting or fines content at a given final freeness compared to the conventional plate. This observation aligns with the work of previous research, which found that optimized plate designs can achieve rapid freeness reduction without compromising final fiber length retention [5], as well as with other studies reporting comparable trends in both hardwood and recycled fiber systems [1,2]. Similarly, at a key production target (e.g., 200 mL CSF), both plates produce similar fiber and fines profiles, indicating no disadvantage in fiber preservation for the ultra-fine bar plate at matched drainage levels [25,26]. Therefore, although the ultra-fine bar plate induces faster fiber shortening at higher refining energies, it preserves fiber length relative to the freeness target, offering the advantage of process efficiency without sacrificing final fiber integrity. This underscores the importance of selecting refining plates that optimize the trade-off between process speed, energy input, and product quality, particularly for recycled KOCC fibers that are sensitive to mechanical treatment [27,28].
Made with FlippingBook flipbook maker