www.nature.com/scientificreports/
Figure 8. Effect of CNF dosage on hydrophobic properties of paper.
Figure 9. Images of contact angle test of ( a ) base paper, ( b ) PVA coated paper, and ( c ) PVA/CNF coated paper.
to decline. It may be due to that the free hydroxyl groups of PVA are completely bound to CNF, and the hydro- philic hydroxyl groups of CNFs are dominant. When the coating weight was 2.0 g/m 2 and the CNF dosage was 3.0%, the Cobb value of coated paper reached the minimum value of 18.37 ± 0.63 g/m 2 , which was 19.00% lower than that of PVA coated paper. When the coating weight was 4.0 g/m 2 and the CNF dosage was 3.0%, the Cobb value of coated paper was 21.80 ± 0.39 g/m 2 , which was 19.31% lower than that of PVA coated paper. As can be seen from Fig. 9, the contact angle of the base paper was 95.21°, the PVA coated paper was 67.82°, and the PVA/CNF coated paper was 93.56°. Figure 9 demonstrated that the hydrophobic properties of the base paper decreased significantly after PVA coating, while the PVA/CNF coated paper basically maintained the hydrophobicity as the base paper. Due to the presence of a lot of free hydroxyl groups in PVA, the hydrophilicity of the paper coating surface is enhanced. However, with the addition of CNFs, the network structure formed between CNFs and CNFs and the hydrogen bonds between CNFs and PVA reduced the free hydroxyl groups on the coating surface, resulting in a better hydrophobic performance of the PVA/CNF coating 53 . Ǥ Figure 10 shows the effect of CNF dosage on the tensile strength of coated paper. As shown in Fig. 10, when the CNF dosage was increased from 0.0% and 3.0%, the tensile index of the coated paper increased significantly with the CNF dosage increased. However, continuing to increase the CNF dosage, the tensile index of the coated paper increased slowly. When the coating weight was 2.0 g/m 2 and the CNF dosage increased from 0.0 to 3.0%, the transverse tensile index of the coated paper increased from 37.63 ± 0.25 N m/g to 40.71 ± 0.78 N m/g (Fig. 10a). Furthermore, when the coating weight was 4.0 g/m 2 and the CNF dosage increased from 0.0% to 3.0%, the transverse tensile index of coated paper increased from 39.56 ± 0.22 N m/g to 42.58 ± 0.48 N m/g. As shown in Fig. 10b, the longitudinal tensile strengths of coated papers with 2.0 g/m 2 and 4.0 g/m 2 were 68.61 ± 0.55 N m/g and 72.11 ± 0.43 N m/g when the CNF dosage was 3.0%. CNFs is rich in hydroxyl groups, which can combine with the fibers on the surface of paper by hydrogen bonding, and improve the bonding force between the fibers, thus improving the tensile strength of paper. In addition, CNFs and PVA form hydrogen bonds, forming a compact film on the paper surface, further improving the tensile strength of the paper 54 .
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(2022) 12:16148 |
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