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Table 3 Zeta potential and surface charge mean values with 95% confidence limit. Note that R30 zeta potential absolute value was affected by the use of a filter paper
Surface charge density ( l ekv/g)
CTMP
PCC-CTMP
Zeta potential (mv) pH EC (mS/cm) Zeta potential (mV) pH EC (mS/cm) CTMP
PCC-CTMP
0 min R30
–5.8 ± 4.3
–1.2 ± 3.9
R100
–7.1 ± 2
–3.4 ± 5.2
R200
–52.2 ± 1
7.3 0.30
–50.3 ± 2.9
8.0 0.29
–9.7 ± 0.9
–3.8 ± 3.2
R400
–29.1 ± 0.6
7.5 0.29
–26.1 ± 0.6
8.0 0.29
–46.9 ± 2.4 –41 ± 2.2
Pass
–20.2 ± 2.5
Not fract –64.9 ± 1.6
6.5 0.30
16.8 ± 0.1
8.1 0.30
–18 ± 0.6
–26 ± 1.6
30 min R30
–20.4 ± 4.4
7.3 0.3
–8.3 ± 3.1
–1.9 ± 5.2
R100
–47.4 ± 1.1
7.6 0.30
–63 ± 2.3
7.9 0.29
–8.2 ± 2.1
2.1 ± 6.4
R200
–48.8 ± 2.2
7.4 0.31
–54.6 ± 1.7
7.9 0.30
–11.3 ± 3.6 –5.2 ± 3
R400
–26.8 ± 0.6
7.4 0.30
–22.8 ± 0
7.9 0.28
–47.3 ± 1.7 –42.1 ± 1.2
Pass
–31.1 ± 4.1
Not fract –55 ± 1.6
6.3 0.3
14.2 ± 1.7
8.5
–21.2 ± 2.7 –20.5 ± 1.2
60 min R30
–13.6 ± 1.1
7.7 0.29
–10.7 ± 4.2 –10.9 ± 4.3
R100
–47.3 ± 1.4
7.5 0.31
–60.8 ± 1.2
8.0 0.30
–12.1 ± 0.5 –9.7 ± 1.5
R200
–51.8 ± 1.6
7.5 0.30
–32.1 ± 0.8
8.0 0.30
–10.8 ± 2.7 –16.6 ± 1.7
R400
–26.8 ± 9.5
7.4 0.30
–23.7 ± 0.4
0.29
–45.9 ± 5.5 –57.6 ± 1.1
Pass
–38.2 ± 1.6
Not fract –44.6 ± 1.7
6.7 0.30
12.4 ± 0.5
8.5 0.30
–27.8 ± 0.4 –15.5 ± 3.4
0 min 30 min 60 min
flux. In addition, the streaming potential method used in this study is affected by fiber pad compression (Hubbe 2006), and the fiber pad compression was visibly dependent on the fraction measured, which may explain why the zeta potential was closer to zero for R30 and R400 than for R100 and R200.
-60
-50
-40
-30
Scanning electron microscopy
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Scanning electron microscopy of the fractionated PCC-CTMP samples further confirmed that the ash content increased with decreasing fiber size, see Fig. 8. The PCC was in the form of typically nano- sized roundish particles and their aggregates or clusters. No variation in PCC morphology or primary particle size was detected between the different fiber fractions, but the larger amount of PCC in the fines fraction suggested that the PCC nanoparticle aggre- gate size perhaps increased.
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0 C P-C C P-C C P-C C P-C C P-C C P-C R30 R100 R200 R400 pass n/f Fig. 7 Surface charge densities of the samples. C refers to CTMP and P-C to PCC-CTMP. The error bars represent 95 % confidence values. n/f = not fractionated
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