1 846
Cellulose (2025) 32:1835–1850
especially true for pulps not severely fibrillated, i.e. , bleached hardwood and recycled pulp. The effect of dewatering time and maximum pul p concentration constants on the vacuum dewatering behaviour of the three pulps [see Eq. (4)] was statis- tically analysed with respect to fibre characteristics. The water retention value and freeness were utilise d to evaluate the extent of fibrillation endured by th e pulps because of refining. This is because change s in these water-fibre parameters are the results o f pulp internal and external fibrillation after refinin g (Abitz and Luner 1989; Gu et al. 2018). Analysi s of covariates (ANCOVA) was utilised to prove tha t there is an effect on the vacuum dewatering con- stants of all three pulps by the freeness and wate r retention value when vacuum pressure is include d as a covariate where P < 0.05. The results are graphically presented in Figs. 8 , 9, 10, and 11 below for visualisation of the effect of freeness on the dewatering time constants of al l three pulps thus exploring how drainabillity of pul p
affects the pulp dry matter achieved during vacuu m dewatering. Bleached hardwood and recycled pulp achieved the same maximum pulp concentration constant of 20% at the lowest vacuum pressure of − 55 kPa gauge as shown in Fig. 9. It could be attributed to the two pulps having the same drainability or freeness o f 37°SR. However, the virgin bleached pulp has the lowest dewatering time constant of 17 ms, thereby indicating quick dewatering when compared to recy- cled pulp with double the dewatering time constant of 34 ms at this pressure. This is demonstrated in Fig. 8. According to the results, bleached hardwood reaches a dewatering plateau at a relatively faster rate. At − 19 kPa gauge, the pulps achieve similar plateau pulp concentrations of 13% (bleached hardwood) and 14% (recycled pulp), with visibly different dewater- ing rates of 43 and 39 ms for bleached hardwood and recycled pulp, respectively. A maximum pulp concen- tration constant of 17% was achieved by both pulps at − 37 kPa gauge with the virgin pulp observing a rela- tively lower dewatering time constant of 21 ms, much
Fig. 8 Effect of freeness o n dewatering time constant
100 120 140 160 180
0 20 40 60 80
33
38
43
48
53
Freeness (°SR)
-19 kPa gauge
-55 kPa gauge
TaoL 19
t-a3o7Lk3P7a gauge
Fig. 9 Effect of freeness o n maximum pulp concentra- tion constant
12 13 14 15 16 17 18 19 20 21
32
37
42
47
52
Freeness (°SR)
MC L 37 -37 kPa gauge
MCL19 -19 kPa gauge
MCL 55 -55 kPa gauge
Vol:. (1234567890)
Made with FlippingBook. PDF to flipbook with ease