Barrios et al. Biotechnology for Biofuels and Bioproducts
(2025) 18:48
Page 10 of 23
Table 5 Combined effect of enzyme and cationic starch dose on EMC and tensile strength of paper for BHW-1k PFI mill refining
Tensile index (Nm/g) Bulk (cm 3 /g)
Enzyme dose (%)
Cationic starch dose (%)
Duration of pretreatment (min)
Freeness (mL)
EMC (%)
Avg
Std
Avg
Std
Avg
Std
Avg
Std
Refined to 1000 rev 0 0
n/a n/a n/a
510 550 570 600 628 629 602 629 630
5 9 6 8 5 6 4 6 5
61.11 58.12 57.69 53.76 50.05 56.73 56.68 55.94 55.56
0.90 1.14 0.76 0.98 1.01 0.90 1.10 1.07 0.73
61.22 73.73 71.83 59.27 76.69 66.45 56.03 71.33 65.13
4.45 3.69 3.60 6.38 4.24 3.11 3.79 4.41 1.94
1.60 1.40 1.42 1.88 1.82 1.79 1.54 1.55 1.54
0.01 0.01 0.02 0.00 0.02 0.02 0.03 0.02 0.02
0.5
1 0
0.5
30 30 30 30 30 30
0.5
1 0
1
0.5
1
Averages and standard deviation with five replicates
timing and method of additive addition is crucial for opti- mizing dewatering rates while maintaining or enhancing paper strength [62]. The results obtained in the present study support such claims. The cell-free enzyme pretreatment was also evaluated at various refining levels on a laboratory scale. After extensive screening of refining levels, temperature, and dosages of chemicals and enzymes (data not shown), the optimal conditions are presented in Table 5. A refining level of 1,000 PFI mill revolutions was identified as optimal. The ideal enzyme and cationic starch dosage combination should achieve minimum EMC, maximum freeness, and maximum tensile strength in the handsheets from the pretreated pulp. The results indicate that the cell-free enzyme pretreatment with 0.5 wt.% enzyme combined with 0.5 wt.% cationic starch yielded the best outcomes. This condition resulted in the lowest EMC (50.05%), a significant increase in tensile strength (~ 25.0%) to 76.69 Nm/g, and an improvement in freeness (~ 23.0%) to 628 mL compared to the control (no enzyme or starch). This demonstrates a positive impact on reducing EMC and enhancing both paper strength and freeness. Notably, the reduction in EMC (~ 11.0% total solids increase) under these conditions suggests an improved dewatering process, which is crucial for efficient paper production. However, increasing the enzyme dosage beyond 0.5 wt.% led to less favorable results, with increased EMC and decreased tensile strength. Specifically, at 1.0 wt.% enzyme dosage, despite a slight increase in freeness, the tensile strength dropped to 66.45 Nm/g, and EMC increased to 56.73%, indicating a trade-off between dewatering and mechanical properties. This finding aligns with the trend observed in previous studies, where increased cationic starch dosage improved freeness but
EMC and paper properties Preliminary tests were conducted at a laboratory scale to determine the optimal dose of the enzyme cocktail to achieve a significant reduction in moisture content after pressing, as shown in Table 4. The pulp samples were refined to 1000 PFI revs before enzymatic treatment. The optimal enzyme dosage was determined by identifying the condition that resulted in the lowest EMC and the highest tensile strength in the paper handsheets. As presented in Table 4, at a 0.5 wt.% enzyme dosage (on an oven-dry pulp basis), there was a significant reduction in EMC from 61.11% (control) to 53.76%, alongside a slight decrease in tensile strength from 61.22 Nm/g to 59.27 Nm/g. This dosage also improved the drainage rate, as evidenced by increased freeness from 510 mL (control) to 600 mL. Increasing the enzyme dosage to 1.0 wt.% resulted in a slight further increase in freeness accompanied by a less desirable outcome: a reduction in EMC (to 56.68%) and a decrease in tensile strength (to 56.03 Nm/g). These results suggest that while a 0.5 wt.% enzyme dosage effectively improves drainage and reduces EMC, higher dosages may negatively impact the paper’s mechanical strength. The enzyme dosages applied in this study, spe- cifically 0.5 and 1.0 wt.% based on dry pulp, correspond to protein concentrations of 0.9 mg and 0.18 mg protein per gram of dry pulp, respectively. These concentrations are similar to those reported in other articles assessing the impact of enzyme treatments on press dewatering with various commercial enzymes [61]. However, differ- ences in the consistency and treatment times between the mentioned study and this one may account for vari- ations in the effectiveness of the enzyme treatments on paper properties observed here. A balance between refin- ing conditions, enzymatic reaction temperatures, and the
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