Cellulose (2025) 32:1835–1850
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(a)
(b)
25
25
20
20
15
15
10
10
5
5
0
50 100 150 200 250
0 50 100 150 200 250
Time (ms)
Time (ms)
(c)
25
20
15
10
5
0
0
50
100
150
200
250
Time (ms)
Mechanical pulp
Recycled pulp
Bleached hardwood pulp Predicted recycled pulp
Predicted mechanical pulp Predicted bleached hardwood
in each case (see Table 3), at vacuum pressures of a − 19 kPa gauge , b −37 kPa gauge and c −55 kPa gauge
Fig. 7 Exponential decay regression plot for predicted pulp concentration. A prediction of pulp concentration for dwell times ranging from t = 0 to t =250 ms with a total of 5 pulses
of − 19 and − 55 kPa gauge for the recycled pulp . Mechanical (groundwood) pulp had the lowes t drainability of 50 SR o because of extreme externa l fibrillation, leading to the highest fines content o f 74% (see Table 4). This resulted in poor vacuu m dewatering where the lowest values of 12.1, 15. 8 and 18.3% were achieved at − 19, − 37 and − 5 5 kPa gauge, respectively. Neun (1996) dewatered newsprint composed of 70% groundwood and 30 % kraft, they discovered that the furnish had the slow- est rate of dewatering and achieved the lowest dry- ness when compared to high-freeness kraft an d repulped old corrugated containers (OCC). The lim- ited dewatering performance of the newsprint coul d
be attributed to the majority groundwood pulp pre- sent in the furnish. Experimental data shows that al l three pulps observed a dewatering plateau for dwel l times ranging from 30 to 135 ms, which is shown i n Fig. 7a–c. The highest pulp concentration values o f 21.8% (bleached hardwood pulp), 19.8% (Recycled pulp) and 18.3% (mechanical pulp) were recorde d at a pressure for − 55 kPa gauge and a dwell tim e of 250 ms for all three pulps as shown in Fig. 7a–c. Therefore, lower vacuum pressures coupled wit h longer dwell times resulted in dryer hand sheet s and therefore high mass concentration for all thre e pulps before their dewatering eventually diminished (Neun 1994, 1996; Räisänen et al. 1995). This wa s
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