PAPERmaking! Vol8 Nr2 2022

www.nature.com/scientificreports/

SBKP

SUKP CTMP

DSUKP

0.000 0.005 0.010 0.015 0.020 0.025

1

2

3

-1 0

Number of cycles

Figure 9. Changes in factor of weakness inter-fiber bond strength during recycling.

recycling treatment tends to increase strengths such as tensile strength and burst strength of papers produced from mechanical pulp. It is considered that lignin was removed by washing in the recycling process and the inter-fiber bonding between pulp fibers was strengthened in the papermaking process of defibration in water, dewatering and drying, which contributed to the improvement of tensile strength. Nazhad 25 showed in experiments on the recycling process of CTMP that the fiber coarseness of CTMP was reduced and the fiber flexibility was added regardless of the degree of delignification treatment with sodium chlorite. Furthermore, it has been reported that in CTMP that has been subjected to the delignification treatment, the strength of the handsheets decreases due to the increase in the number of recycling, regardless of the amount of lignin content. On the other hand, in the CTMP experiment of this study, it was confirmed that the tensile strength of the handsheets tends to increase or relatively little change as the number of recycling increases. On the other hand, in the CTMP experiment of this study, it was confirmed that the tensile strength of handsheets tends to increase or relatively little change as the number of recycling increases. The effect of the recycling treat- ment on the tensile strength of the CTMP handsheets obtained in this study is different from that of SUKP and DSUKP because the wettability on the surface of the CTMP fiber improved and the fiber–fiber bond strength increased as the number of recycling increased. ơ‡ –‘ˆ”‡ › Ž‹‰–”‡ƒ–‡–‘Ƥ„‡”ȂƤ„‡”„‘†•–”‡‰–Š‹’ƒ’‡”•Š‡‡–•Ǥ To clarify the fac- tors that influence the tensile strength of paper sheets, the Page equation 17,31 has been proposed. Furthermore, Cildir et al. 16 applied the Page equation below to calculate the fiber–fiber bond strength from the viewpoint that the resistance to fracture consists of two comparable resistances. It was presumed that the decrease in tensile strength was mainly the decrease in the fiber–fiber bond strength.

(2)

1 / T = 1 / F + 1 / B

(3)

F = 8Z / 9

where T: tensile index of sheet, F: fiber strength index of sheet, Z: zero-span tensile index of sheet, B: bond strength index of sheet. Using Eqs. (2) and (3), it should be possible to calculate the fiber–fiber bond strength index of sheet, B, if the tensile strength of sheet, T and the zero-span tensile index, Z are measured. Figure 9 shows the effect of the number of recycling treatments on the fiber–fiber bond strength index. As the number of recycling treatments increased, the factor of fiber–fiber bond weakness (1/B) of all SKP paper sheets tended to increase, and it became clear that the fiber–fiber bond strength became weaker. In addition, 1/B of DSUKP was lower than that of SUKP. By applying the delignification treatment, the lignin content in the paper sheet is reduced and the formation of fiber–fiber bonds is promoted. Comparing 1/B of SBKP and DSUKP, despite the fact that the DSUKP had a smaller of 1/B and a higher lignin content in pulp (Table 1), the result was obtained that the fiber–fiber bond strength of DSUKP was higher. On the other hand, in the CTMP paper sheet, 1/B decreased with the number of recycling, which means that the fiber–fiber bond strength in the paper sheet was improved. ơ‡ –‘ˆ•—”ˆƒ ‡™‡––ƒ„‹Ž‹–›‘ˆ™‘‘†’—Ž’Ƥ„‡”•‘Ƥ„‡”ȂƤ„‡”„‘†‹‰’‘–‡–‹ƒŽǤ The tensile strength of the paper sheet, the wettability of the pulp fiber, and the change in the bond strength between the pulp fibers in the paper sheet were evaluated by the recycling experiment of the SKP pulp fiber, and the cor- relation was examined. When all the values were evaluated for each sample used in this study, the correlation between the tensile strength of the sheet and the fiber–fiber bond weakness index was R 2 = 0.98 (Fig. 10). The p value of the correlation coefficient was 0.000, which was judged to be significant at the 5% significance level. Therefore, it was found that the correlation between the tensile strength of the sheet and the fiber–fiber bond strength is considerably high. When the relationship between 1/B and the contact angle of water with respect to the pulp fiber in the SKP sample was examined, R 2 = 0.71 was obtained (Fig. 11). In this case, the p value was 0.004, which was significant

 ‹‡–‹Ƥ ‡’‘”–• |

Š––’•ǣȀȀ†‘‹Ǥ‘”‰ȀͷͶǤͷͶ͹;Ȁ•ͺͷͻͿ;ǦͶ͸͸ǦͶͻͻͷͺǦ͸

;

(2022) 12:1560 |

Vol:.(1234567890)

Made with FlippingBook - Online magazine maker