www.nature.com/scientificreports/
80
70
R² = 0.9804
60
50
40
0.0
0.5
1.0
1.5
Factor of weakness, 1/Bx10 -2 Figure 10. Factor of bonding weakness, 1/B versus tensile index of SKP handsheets.
60
40
20
R² = 0.7145
0
0.0
0.5
1.0
1.5
Factor of weakness, 1/Bx10-2 Figure 11. Factor of bonding weakness, 1/B versus water contact angle after contact 1 s (SKP).
when the t test was performed ( p < 0.05). It was found that it was not uncorrelated, and it was confirmed that the correlation between the two factors was relatively high. Therefore, it was clarified that the better the wettability of the pulp fibers, the easier it is to form fiber–fiber bonds and the greater the tensile strength of the paper sheet. In addition, it was speculated that the main cause of the decrease in the tensile strength of the paper sheet due to recycling was the decrease in the fiber–fiber bond strength of the paper sheet, and that the decrease in the fiber–fiber bond strength was related to the decrease in the wettability of the pulp fibers. Pulp samples prepared from softwood bleached kraft pulp (SBKP), softwood unbleached kraft pulp (SUKP) with different lignin contents and chemi-thermomechanical pulp (CTMP) are subjected to one or three repeated wet and dry treatments. The contact angle of water with respect to each pulp fiber over time was measured. Further- more, the effect of the wettability of pulp fibers on the tensile strength of the paper sheet was evaluated from the change in the fiber–fiber bond strength based on the Page equation. 1. In the case of the SBKP, repeated dry and wet recycling treatment increased the contact angle of water with fibers and reduced wettability. The pulp fiber (R3) that had been recycled three times maintained a contact angle similar to that of R1 within 1–3 s after contact. After 4 s of contact, it was smaller than the contact angle of the pulp fibers (R1) that had been recycled once. On the other hand, the CTMP fiber showed a different behavior from the softwood kraft pulp fiber (SKP) because the contact angle with water decreased as the number of recycling increased. 2. The tensile strength of softwood kraft pulp (SKP) paper sheets, including paper sheets prepared from bleached, unbleached and delignified pulp, tended to decrease as the number of recycles increased. On the other hand, in the paper sheet prepared from CTMP, the tensile strength tends to increase slightly as the number of recycling increases, suggesting that the fiber–fiber bond may be strengthened. 3. By measuring the tensile strength and zero-span tensile strength of a paper sheet prepared from recycled softwood kraft pulp (SKP) fibers and applying it to the Page equation, the change in the contact angle of water with respect to the pulp fiber over time can be determined. The effect of the wettability of pulp fibers on the tensile strength of paper, especially the fiber–fiber bond strength, was evaluated. As a result, the tensile strength of the paper sheet from the recycled SKP pulp fibers
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Ϳ Vol.:(0123456789)
(2022) 12:1560 |
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