Barrios et al. Biotechnology for Biofuels and Bioproducts
(2025) 18:48
Page 11 of 23
Table 6 Effect of cell-free enzyme pretreatment on 1k-refining BHW fibers’ dimensional characteristics Enzyme dose (%) Cationic starch dose (%) Mean weighted fiber length (μm) Mean fiber width (μm) Mean Kink Index (1/mm)
Mean Curl Index (L w ) Fines content (L w %)
Avg
Std
Avg
Std
Avg
Std
Avg
Std
Avg
Std
Refined to 1000 revs 0 0
997 994 974 994 991 981 973 987 996
21 28 16 19 20 15
18.90 19.35 18.65 18.35 19.14 19.35 18.65 18.45 18.36
0.14 0.21 0.07 0.35 0.19 0.31 0.06 0.18 0.07
1.57 1.48 1.43 1.36 1.53 1.44 1.32 1.62 1.53
0.01 0.02 0.01 0.01 0.02 0.02 0.01 0.02 0.01
0.081 0.080 0.077 0.070 0.071 0.080 0.087 0.086 0.077
0.002 0.001 0.005 0.004 0.002 0.001 0.004 0.004 0.005
5.23 4.89 3.92 9.93 3.56 3.38
0.06 0.18 0.09 0.13 0.47 0.37 0.31 0.08 0.45
0.5
1 0
0.5
0.5
1 0
1
7
10.93
0.5
23 21
4.65 3.72
1
wet-pressing, allowing quicker water removal without compromising the paper’s mechanical properties [66]. However, it is essential to carefully control enzyme dos- age and refining conditions to prevent over-hydrolysis of fibers, which could negatively impact the paper’s strength and runnability [67]. Cell-free enzymatic fiber modification for enhanced dewatering Fiber dimensions The effect of enzyme cocktail and cationic starch dosage on the dimensional properties of 1k-refining bleached hardwood (BHW) pulp fibers is presented in Table 6. No significant change in the mean weighted fiber length was detected when comparing the control sample (0 wt.% enzyme, 0 wt.% cationic starch) with the best performing condition (0.5 wt.% enzyme, 0.5 wt.% cationic starch). The average fiber length for all conditions remained close to 990 μm, with the standard deviation indicating minimal variability. This stability in fiber length suggests that the 1k mild refining conditions, in conjunction with the enzymatic and cationic starch treatments, did not cause excessive fiber shortening, which is crucial for maintaining the paper’s tensile strength [64]. Similarly, the cell-free enzyme pretreatment caused only minor changes in fiber width. The width values before and after pretreatment were around 18.9 μm for all conditions, with only slight variations observed. This consistency in fiber width indicates that the enzymes did not significantly contribute to the fibers’degradation, which could otherwise compromise the dewatering and physical properties of the paper [68]. More pronounced effects were observed in the kink and curl indexes of the fibers. The enzymatically treated samples consistently exhibited lower kink and curl
required careful balancing to avoid compromising other paper properties [63]. The significant enhancement in tensile strength suggests improved fiber bonding, probably due to the enzyme’s ability to modify the fiber surfaces, facilitating better interaction with the added cationic starch. It can be attributed to the enzymatic action that likely involves a controlled modification of the hemicellulose and cellulose components of the fibers. Cellulases and xylanases act synergistically to selectively degrade specific fiber components, leading to a more favorable fiber morphology for bonding and a better surface area for interaction with cationic starch. This synergy between cellulase and xylanase enzymes is critical in enhancing fiber flexibility and reducing fiber stiffness, which contribute to improved inter-fiber bonding and, consequently, higher tensile strength [64]. Furthermore, the increase in tensile strength observed in this study aligns with findings from previous research, which demonstrated that enzyme treatments could significantly improve paper strength when combined with refining and appropriate chemical additives [65]. The effectiveness of enzyme treatment also depends on achieving a delicate balance between refining conditions and enzymatic pretreatment. Refining is known to increase the fiber surface area and promote fibrillation, which can be further enhanced by enzymatic treatments to optimize fiber bonding and reduce the need for excessive refining, which could damage fibers and reduce paper strength. In addition to the increase in tensile strength, the observed changes in bulk indicate that the enzyme treat- ment effectively modified the fiber structure, potentially leading to a more open and porous fiber network. This is crucial for enhancing dewatering efficiency during
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