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Cellulose (2025) 32:1835–1850
Pulp samples in the form of slurry were prepared per ISO 16065-2:2014 to achieve a mass concentra- tion and volume of 0.1% and 100 mL, respectively. This was done to determine fibre morphological properties such as fibre length, shape factor and fines content. These properties were obtained at each refin- ing stage of the pulps using data that was collected from the Lorentzen and Wettre fibre tester (ABB 2020). The morphological properties are defined by Lorentzen and Wettre fibre tester as specified by ISO where fibres are classified as having a length range of 0.2–7.5 m m (ABB 2020). The fibre tester categorises fibres with a length that is less than 0.2 mm as fines in accordance with ISO (ABB 2020). The pulp freeness was tested following a procedure described in the technical information document ISO 5267-1:2001. Freeness is a measure of the drainabil- ity of pulp and can be acquired using the Schopper Riegler (°SR) method. It is important to note that the higher the value in °SR, the lower the drainability of the pulp whereas the opposite is true for low °SR values. The water retention value is a parameter that indi- cates how well water is bound in fibres (Sundblad 2015). It is measured as the ratio of mass of water per unit mass of dry fibre. A centrifuge was utilised to determine the parameter as illustrated in ISO 23714:2014, where a pulp pad with a grammage of 1700 g/m 2 at a diameter of 30 mm was placed in t he equipment to be centrifuged at a force of (3000 ± 50) g for 30 min ± 30 s at a temperature of (23 ± 3) °C where g is the gravitation acceleration. The parameter was computed as shown in Eq. (2).
suitable for board manufacturing. The chosen gram- mage to achieve the desired mass was 170 g/m 2 a s shown in Table 1. Formed sheets were placed on the sample holder above the chamber housing the spin- dle, after which they were dewatered at room tem- perature. The dewatered hand sheets were weighed before being placed in an oven to dry overnight at 105 °C ± 2 °C. The oven dry mass was measured to enable computation of the outlet mass concentration according to Eq. (3). Test conditions during vac- uum dewatering of pulp hand sheets are provided in Table 3.
m
f
(3)
× 100
m
c =
m
i
wher e m c , m f an d m i represent the outlet pulp con- centration (%), oven-dry mass and sample mass after vacuum dewatering in grams, respectively.
Results and discussion
Pulse generation
Pressure profiles achieved during drying of the hand sheets using the laboratory suction box are presented below. Reflected in Fig. 2 is a pressure profile at a vacuum pressure of − 55 kPa gauge for a dwell time of 30 ms. Five pulses were specified during all tests, resulting in a 6 ms individual vacuum pulse for a total dwell time of 30 ms. Figure 2 shows that more than five pulses were observed out of the test bound- ary, which is due to the spindle rotating before the vacuum chamber was fully evacuated to the desired pressure of − 55 kPa gauge. Residual pulses also occurred as the spindle continued rotating during
m
1
(2)
− 1
WRV =
m
2
wher e m 1 an d m 2 represent the pad mass after cen- trifugation and oven drying, respectively.
Table 3 Vacuum dewatering test conditions Parameter Value
Hand sheet formation and vacuum dewatering methodology Hand sheets were formed to a pulp concentration of approximately 7% according to the procedure i n TAPPI T-205:2006 where sheets with a diameter of 150 mm and an approximate mass of 3 g were pre- pared, which is the recommended mass for pulps
Temperature (°C)
Room (21–28) − 19, − 37, − 55 30[6], 70[14], 110[22], 135[27], 250[50]
Vacuum pressure (kPa gauge)
Dwell time [Single Pulse time] (ms)
Sample diameter (mm)
150 170
Grammage (g/m 2 )
Vol:. (1234567890)
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