The pulps SCB were bleached using an elemental chlorine-free sequence ODP2 according to [76, 77] (Table 4.11 and Figures 4.14 and 4.15).
2 Bleaching process is the next step which may be applied to brown pulp in order to improve brightness and to make it appropriate for paper making operations. In this regard, several bleaching agents can be used, such as chlorine, chlorine dioxide, hydrogen peroxide, oxygen, ozone, etc., through elemental chlorine free (ECF) or total chlorine free (TCF) bleaching processes. ECF is mainly conducted by using ClO2 and H2SO4 in an acidic environment or NaOH, which is often combined with O2, and hydrogen peroxide in an alkaline phase are used to enhance the extraction stage of the lignin oxidation. In TCF, different combination patterns of bleaching acid (H2SO4), ozone, O, chelating agents, and/
or hydrogen peroxide (P) steps are used. P is an oxidant compound which has been widely applied for pre-delignification of chemically produced pulps, in bleaching sequences.
Figure 4.14 Material balance in the ECF bleaching for SCB pulps.
918.5 kg Whole bagasse
51.4% fiber 36.7% pith 11.9% soluble
Wet, dry and moist depithing
Plup mixer
1000 kg SCB-OCC
Synergistic delignification 170° , 30 minutes,
7 Kg/cm2
604 kg SCB-OCC plup
Kappa: 18.7 Rejects: 1.8%
Viscosity: 24.6CP Whiteness: 46%
Oxygen (O) 100°, 60 minutes,
4 Kg/cm2, plup consistency 10%
pH 12.7
0.054 g/L NaOH pH:10.1
0.008g/L CIO2 (99.5%) pH: 5.3
0.12g/L NaOH 0.6g/L H2O2 (85.3%)
pH: 11 577.8 kg
Kappa: 6
561.7 kg Kappa: 3.6
552.1 kg Bleached SCB-OCC pulp
Viscosity: 8.78 CP Whiteness: 85.6%
Opacity: 78.6 1.2% NaOH
0.05% MgSO4
1.5% Na2SiO3 2% NaOH 0.05% MgSO4 White liquor
13% NaOH Liquor/ fiber ratio 10:1
200 kg OCC pulp Repulping
84.8% yield 235.9 kg
OCC Kraft liner 55.5% Long fiber
Peroxide (P) 70°, 180 minutes, 2.5% (H2O2), pulp consistency 10%
pH 11.4 Chlorine dioxide (D)
70°, 180 minutes, 0.9% (CIO2), pulp consistency 10% pH
7.5
Black liquor 3.28 g/L NaOH
pH: 12.3 ρ: 1.019 g/cm3 800 kg
dephited bagasse 87.1% fiber 10.6% pith 2.1% soluble
Bleached SCB pulps were refined at a consistency of 10% to obtain a refining curve, later forming hand sheets, respectively, based on 60 g/m2 for physical tests of strength and drainability properties. The refining behavior of the pulps is shown in Tables 4.12–4.19 and Figures 4.16–4.23.
This process is mainly used to decrease the kappa number and increase the brightness and stability of the produced pulps. Washing the produced pulps (e.g., by using an alkali caustic soda) is then applied to remove the bleaching agents and hardly biodegradable compounds [78].
Figure 4.15 (a) Conventional soda SCB pulp, (b) SCB–OCC pulp, (c) bleached ECF SCB pulp, and (d) Bleached ECF SCB–OCC pulp.
(a) (b)
(c) (d)
Table 4.12 Pulp-refining degree (Schopper–Riegler °S.R.) Refining (min) 100%
OLD–SCB
100% FRESH SCB
80/20%
SCB–OCC
0 21 20 19.5
1 25 22.5 22.5
2 33 25 25.5
5 43 34 29
7 50 38 32
Table 4.13 Freeness (mL C.S.F.).
Refining (min) 100%
OLD–SCB
100% FRESH SCB
80/20%
SCB–OCC
0 574 593 602
1 504 547 547
2 388 504 496
5 275 375 443
7 211 328 401
Table 4.14 Breaking length (m).
Schopper–
Riegler °S.R.
100%
OLD–SCB
100% FRESH SCB
80/20%
SCB–OCC
20 4030 5070 4392
25 5070 6727 6629
29 6109 7140 7909
33 7149 7656 7413
Table 4.15 Burst index (kPam2/g).
Schopper–
Riegler °S.R.
100%
OLD–SCB
100% FRESH SCB
80/20%
SCB–OCC
20 2.75 4.17 4.13
25 3.41 5.72 5.65
29 4.07 6.09 6.40
33 4.73 6.56 6.18
Table 4.16 Tear index (mNm2/g).
Schopper–
Riegler °S.R.
100%
OLD–SCB
100% FRESH SCB
80/20%
SCB–OCC
20 7.52 8.50 11.93
25 5.81 7.85 11.44
29 5.53 7.27 9.01
33 5.23 6.54 8.83
Table 4.17 Folding endurance (double folds).
Schopper–
Riegler °S.R.
100%
OLD–SCB
100% FRESH SCB
80/20%
SCB–OCC
20 34 127 143
25 52 321 672
29 70 322 598
33 88 367 414
Table 4.18 Porosity (s/100 cm3).
Schopper–
Riegler °S.R.
100%
OLD–SCB
100% FRESH SCB
80/20%
SCB–OCC
20 11 11 7
25 63 58 23
29 149 106 40
33 53
Table 4.19 Drainage time of pulp (s).
Schopper–Riegler
°S.R.
100%
OLD–SCB
100% FRESH SCB
80/20%
SCB–OCC
20 5.09 5.21 5.04
25 6.11 6.86 6.07
29 7.19 7.53 6.71
33 8.27 8.19 7.16
Figure 4.16 Pulp-refining degree (Schopper–Riegler °S.R.).
0 10 20 30 40 50 60
0 1 2 5 7
Pulp-refining degree (Schopper–Riegler °SR)
Refining time (Minutes)
100 % OLD SCB 100 % FRESH SCB 80/20 SCB-OCC
These combination processes (alkaline delignification and bleaching) were found to be effective in improving strength, optical, and drainage properties of SCB–OCC furnishes in relation a conventional SCB pulps.
In this way, employment of OCC in stock preparation as a large fiber fur- nish in bleached paper grades with SCB pulps will be technically possible, because the pulping and bleaching conditions are milder and less cooking chemicals are needed, as compared to wood pulp with the reduction of
Figure 4.18 Breaking length (m).
0 1000 2000 3000 4000 5000 6000 7000 8000 9000
20 25 29 33
Breaking Length (m)
Schopper–Riegler (°S.R.)
100 % OLD SCB 100 % FRESH SCB 80/20 SCB-OCC Figure 4.17 Freeness (mL C.S.F.).
0 100 200 300 400 500 600 700
0 1 2 5 7
Freeness (mL)
Refining time (Minutes)
100 % OLD SCB 100 % FRESH SCB 80/20 SCB-OCC
damage SCB pulps in order to obtain a high-brightness pulp and higher stretch and drainability properties.
Regarding paper properties, FRESH SCB and Bleached 80/20 SCB–OCC pulps have high bulk and at 20°S.R. already have good strength properties.
They require less energy for refining and have a significantly higher tear, folding endurance, burst, tension, and porosity and lower resistance to drainage along development of refining at all levels of Freeness. OLD–SCB pulp at high refining degrees, drainage time for sheet formation increased
Figure 4.19 Burst index (kPam2/g).
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00
20 25 29 33
Burst Index (kPam2/g)
Schopper–Riegler (°S.R.)
100 % OLD SCB 100 % FRESH SCB 80/20 SCB-OCC
Figure 4.20 Tear index (mNm2/g).
0.00 2.00 4.00 6.00 8.00 10.00 12.00
20 25 29 33
Tear Index (mNm2/g)
Schopper–Riegler (°S.R.)
100 % OLD SCB 100 % FRESH SCB 80/20 SCB-OCC
very strongly, tear decreased with refining and folding endurance, burst, and tension increase slightly.