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Cellulose (2019) 26:3473–3487
Fig. 4 Tensile index (Nm/ g) versus density (kg/m 3 ) of handsheets sprayed with the different polysaccharide solutions. The paper properties were measured after restrained (R) and unrestrained (UR) drying. Ref reference samples. The average values with their standard deviations are shown
Table 3 The mechanical properties of handsheets after restrained drying
Density kg/m 3 Tensile index
Tensile stiffness
Strain at break
1D shrinkage
Air permeability
Restrained drying
Nm/g s kNm/g s % s %
mL/min s
Reference
394.5
58.8 2.3 4.2
0.8 6.7 0.6 nd
2868 367
Reference-sprayed
406.4
57.2 3.1 4.4
0.2 5.8 0.6 1.0
4020 380
2% Alginate ( ? 20% sorbitol)
493.1
74.7 3.1 5.1
0.2 5.2 0.3 0.7
503
28
2% Alginate ( ? 30% sorbitol)
507.0
88.1 5.2 5.8
0.1 5.4 0.5 0.2
413
50
4% Alginate ( ? 20% sorbitol)
495.3
84.0 3.8 5.6
0.2 5.3 0.4 0.1
276
58
4% Alginate ( ? 30% sorbitol)
484.6
81.4 6.8 5.5
0.2 5.0 0.7 0.2
382
53
2% Cationic guar gum ( ? 20% sorbitol) 441.5
66.4 3.2 4.3
0.4 6.0 0.5 1.2
2148 229
2% Cationic guar gum ( ? 30% sorbitol) 430.3
64.4 4.1 4.2
0.1 6.1 0.4 1.8
2366 347
4% Cationic guar gum ( ? 20% sorbitol) 448.0
68.2 3.9 5.2
0.1 4.9 0.4 1.1
2135 321
4% Cationic guar gum ( ? 30% sorbitol) 461.5
65.6 2.3 4.3
0.3 6.0 0.3 1.1
1805 193
2% Chitosan ( ? 20% sorbitol)
445.3
76.3 2.6 4.3
0.2 6.6 0.4 nd
2808 283
2% Chitosan ( ? 30% sorbitol)
429.6
62.9 1.2 3.8
0.3 6.1 0.5 1.3
2660 230
4% Chitosan ( ? 20% sorbitol)
457.0
66.0 3.8 4.9
0.1 4.7 0.3 nd
3180 169
4% Chitosan ( ? 30% sorbitol)
440.3
71.9 4.2 4.8
0.1 5.0 0.4 0 5
3212 314
The average values, as well as their standard deviations (s) are reported. The additions were calculated as wt% of o.d. pulp
additions increased the tensile index of the sheets after unrestrained drying. Alginate resulted in the largest increases in tensile index also in this case, but the differences to cationic guar gum and chitosan were quite small. It was previously reported that spray addition of 2 or 4% agar was only able to increase the tensile index of paper by approximately 3 Nm/g after wet-pressing, unless a cross-linker was added (Vishtal and Retulainen 2014a). Additions of 4% agar ?
density (Fig. 4). The density of the handsheets was significantly lower due to the considerable paper shrinkage during the drying process. It is known that unrestrained drying alters the mechanical properties of paper quite significantly (see e.g. Strand et al. 2017). When comparing the untreated reference sheets with reference sheets sprayed with tap water, it was seen that the spraying procedure alone lowered the density of the handsheets (Fig. 4). All of the polysaccharide
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