7218
Cellulose (2020) 27:7215–7225
Table 2 Fiber properties of the recycled board pulp ground with a fine friction grinder including standard deviation of measurements
Sample Fiber length (mm)
Fiber width ( l m)
Fines A1, 0–0.04 mm (%)
Fines A2, 0.04–0.08 mm (%)
Fines A3, 0.08–0.12 mm (%)
Fines A4, 0.12–0.16 mm (%)
Fines A5, 0.16–0.20 mm (%)
T0
0.763 ± 0.018 19.27 ± 0.70 1.94 ± 0.24 1.25 ± 0.07
0.85 ± 0.04 0.68 ± 0.04
0.65 ± 0.03
T1
0.148 ± 0.001 6.42 ± 0.04 20.72 ± 0.09 11.39 ± 0.04
5.7 ± 0.02 3.69 ± 0.03
2.72 ± 0.02
T2
0.053 ± 0.002 3.60 ± 0.10 44.63 ± 1.19 22.93 ± 0.27
9.47 ± 0.32 4.91 ± 0.18
2.87 ± 0.14
T3
0.042 ± 0.002 2.14 ± 0.09 64.77 ± 2.25 24.41 ± 0.94
7.06 ± 0.77 2.18 ± 0.35
0.69 ± 0.15
U0
0.787 ± 0.033 19.53 ± 0.84 1.42 ± 0.16 1.02 ± 0.04
0.74 ± 0.03 0.69 ± 0.02
0.64 ± 0.01
U1
0.138 ± 0.003 6.66 ± 0.09 22.96 ± 0.21 11.87 ± 0.09
6.45 ± 0.08 4.35 ± 0.08
3.11 ± 0.07
U2 0.057 ± 0.001 4.39 ± 0.11 38.96 ± 0.87 20.91 ± 0.43 10.01 ± 0.26 5.94 ± 0.16
4.00 ± 0.01
U3
0.037 ± 0.001 1.87 ± 0.09 72.51 ± 1.89 21.37 ± 1.26
4.58 ± 0.46 1.05 ± 0.12
0.26 ± 0.03
Table 3 Energy consumption of the CNF production and the strength properties of the CNF nanopapers including standard deviation of measurements
Tensile strength (MPa)
Strain (%)
Sample Description Grinding time (min)
Energy consumption (kWh/ kg)
Density (kg/ m 3 )
T0
Fibers
0
0
568.4 ± 8.0 14.0 ± 0.1
1.32 ± 0.01
T1
CNF
37
1.6
881.9 ± 26.6 66.0 ± 3.4
2.54 ± 0.01
T2
CNF
67
3.7
1220.0 ± 6.4 156.1 ± 12.6
7.61 ± 0.09
T3
CNF
114
8.8
1459.2 ± 0.4 181.8 ± 24.1
9.95 ± 0.13
U0
Fibers
0
0
597.5 ± 24.4 16.7 ± 0.4
1.12 ± 0.01
U1
CNF
30
1.0
832.1 ± 42.0 36.7 ± 0.6
1.89 ± 0.01
U2
CNF
60
2.6
1109.9 ± 67.3 102.7 ± 6.8
5.46 ± 0.02
U3
CNF
135
9.9
1418.1 ± 23.0 154.2 ± 18.4
9.35 ± 0.16
conditions of 23 C and 50% relative humidity. After preconditioning for at least 48 h in the standard environment, five thicknesses of the sample in differ- ent locations were measured using a precision thick- ness gauge (Hanatek FT3, UK), and the results were averaged. Six strips with a width of 5 mm were used for the actual strength measurements. The tensile tests were performed with a Zwick D0724587 (Switzer- land) universal material testing machine using a 100 N load cell (Table 3). During the tensile tests, six replicates of each sample were tested using the standard conditions of 23 C temperature and 50% relative humidity. The gauge length was adjusted to 40 mm at a strain rate of 4 mm/min.
The surface structure of different handsheets was visualized directly from the surface of the prepared handsheets, which were sputtered with platinum before observation under the FESEM with 5 kV voltage.
Testing the strength properties of the nanopapers produced from board treated with CNF
Nanopapers were produced by filtration of 0.3 g (abs) of the fibrillated board samples on a polyvinylidene fluoride membrane (Durapore) with a pore size of 0.65 l m and a diameter of 70 mm. After filtration, the wet sheets were covered with a similar membrane and then dried with a Rapid–Ko¨then sheet dryer (Karl Schro¨der KG, Germany) under a vacuum of 0.1 bar at a temperature of 93 C for 10 min (ISO 5269-2:2004). The samples were stored at ISO 187 standard
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