Barrios et al. Biotechnology for Biofuels and Bioproducts
(2025) 18:48
Page 13 of 23
a
b
0E, 0.5 S
0E, 0S
Increased smoothness
50μm
50μm 0.5E, 0.5S
c
d
0.5E, 0 S
Increased entanglement
Increased fibrillation
50μm
50μm
Fig. 3 SEM images of 1k-PFI refined bleached hardwood fibers treated with different enzyme (E) and cationic starch (S) doses: a Untreated control (0E, 0S); b 0E, 0.5S—increased smoothness; c 0.5E, 0S—increased fibrillation; d 0.5E, 0.5S—increased fiber entanglement. Arrows indicate key morphological changes
(Fig. 3a) appeared relatively smooth, with low levels of fibrillation and delamination, alongside several structural irregularities. This smoothness suggests limited surface area exposure and minimal mechanical bonding poten- tial, which may result in weaker inter-fiber adhesion in the final paper product. In contrast, fibers treated with cationic starch (Fig. 3b) showed increased smoothness, flexibility, and better adhesion between adjacent fibers. The cationic starch likely acts as a bonding agent, pro- moting closer contact between fibers and improving the overall strength of the paper. Enzymatically treated fib- ers (Fig. 3c, d) displayed a significant increase in surface roughness, improved fibrillation, and greater delami- nation, which indicate effective enzyme action. The enhanced fibrillation observed in Fig. 3c suggests that the enzyme treatment has facilitated the partial hydrolysis of the fiber surface, exposing more cellulose microfibrils and increasing the fiber’s ability to bond with other fib- ers. This is consistent with findings from other studies, where enzyme treatments have been shown to enhance fibrillation and surface area, leading to stronger paper products [79].
measured charge corresponds to surface charge rather than total charge. This study is the first to directly relate charge analysis to moisture content reduction after wet- pressing, building on the established understanding that charge neutralization is critical in dewatering enhancement. Fiber morphology Various authors have visually assessed the hydrolytic effect of cellulases on cellulose model substrates, revealing significant morphological changes [74]. However, detecting these changes on the more complex surfaces of wood pulp fibers presents a substantial challenge [75–77]. For instance, Suchy et al. demonstrated that high enzyme dosages can induce notable morphological − alterations, such as cell wall dislocations and surface disruptions in the form of cracks [78]. These microstructural changes are critical to understanding the underlying mechanisms of fiber modification during enzyme treatment. Scanning electron micrographs of handsheets formed from cell-free enzyme-treated fibers are presented in Fig. 3. The surface of non-enzymatically treated fibers
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