Barrios et al. Biotechnology for Biofuels and Bioproducts
(2025) 18:48
Page 15 of 23
Fig. 5 Effect of cell-free enzyme treatment on HexAs content of the fibers
Fig. 6 Effect of cell-free enzyme pretreatment on WRV, HRW, FBW, and NFBW content of the fibers. The cationic starch (S) and enzyme (E) dosages are indicated in the x -axis
facilitating the removal of these hydrophilic groups, lead- ing to an enhancement in paper web dewatering.
When examining the effects of the cell-free enzyme pretreatment, the WRV for the sample treated with 0.5% enzyme without starch (0.5E, 0S) was slightly reduced to 2.21 g water/g dry sample, compared to the refined fibers without enzyme treatment. This reduction suggests that the enzyme pretreatment might have cleaned the fiber surfaces by removing fines and partially hydrolyzing the fiber walls, thereby reducing the fiber’s capacity to hold water. This aligns with results reported elsewhere, where enzyme treatments were shown to modify the fiber surface, leading to changes in water retention behavior [93]. Interestingly, the combination of 0.5% enzyme and 0.5% starch (0.5E, 0.5S) resulted in the lowest WRV among the refined samples, with a 1.89 g water/g dry sample value. This significant reduction indicates a synergistic effect between the enzyme and starch treatments, where the enzyme likely facilitates the adsorption of the cationic starch onto the fiber surface. The starch then shields the hydrophilic groups on the fibers, reducing their interaction with water [94]. This result supports the hypothesis that cationic starch can effectively reduce water retention when combined with appropriate enzymatic pretreatments. This strategy can be beneficial in enhancing the efficiency of the papermaking process by reducing the energy required for drying. Hard-to-remove water After moving across the press section and passing through several press rollers, the paper web enters the dryer section of the paper machine. As an initial approach to understanding the effect of the cell-free enzyme process on fiber dewatering in the dryer section,
Mechanical dewatering and thermal drying Water retention value (WRV)
After moving across the forming section, passing through foils and vacuum boxes, the paper web goes through a couch roll and enters the press section of the paper machine. As an initial approach to understanding the effect of the cell-free enzyme process on fiber dewater- ing in the press section, measurements of water retention value were conducted; the results are shown in Fig. 6. Previous studies have shown that enzymatic treatments can reduce WRV by modifying the fiber surface and internal structure, improving dewatering [17, 18]. The WRV is a critical parameter that measures the ability of cellulosic fibers to retain water after being subjected to centrifugal force [91]. Its importance cannot be over- stated, as it is closely related to the fiber’s internal struc- ture, surface area, and chemical composition, making it an essential indicator of the fiber’s behavior during the papermaking process. WRV is used as an indicator of how easily water can be removed from the pulp in the forming and press sections. For unrefined fibers, the WRV was found to be 1.98 g water/g dry sample, which is typical for unrefined fibers, as their surface area and exposure of hydroxyl groups are limited compared to refined fibers [17]. Refining, which involves mechanical treatment to fibrillate the fibers and increase their surface area, significantly increases the WRV. This increase is consistent with previous findings, where refining enhances the fiber’s ability to retain water due to increased fiber swelling and creating more internal spaces within the fiber structure [92].
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