Cellulose (2021) 28:5807–5826
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CTMP 0 min
PCC-CTMP 0 min PCC-CTMP 30 min PCC-CTMP 60 min
content of the fraction increased with increasing mesh number. The ash contents of the samples refined for 30 and 60 min were essentially identical, although the 30 min sample fractions had a slightly higher per- centage of total ash. This was explained by slightly better retention of ash in non-pass fractions in 30 min refined sample, and the slightly higher total ash of the 60 min refined sample.
CTMP 30 min
CTMP 60 min
100
80
60
40
Fiber analysis
20
The average fiber length, fiber width, shape factor, amount of fines and kink index are shown in Table 2. Refining of the unfractionated CTMP reduced the fiber length, fiber width and kink index, but increased the shape factor and amount of fines. Similar changes were detected for the PCC-CTMP, although the change in fiber width was negligible. Comparison of the unfractionated CTMP and PCC- CTMP showed that the fiber length was unaffected by precipitation process of PCC. The fiber width, shape factor and amount of fines increased, but the kink index decreased. The changes caused by precipitation in width and shape factor were however very small: the maximum change detected for these values was 6.4 % increase in width. The differences between the unfractionated PCC and PCC-CTMP were similar to those observed between the fractions. The fiber length in each fraction decreased slightly with refining, but no differences were seen between the CTMP and PCC-CTMP fractions. The main difference was in the fines content of the fractions. The CTMP fractions had more fines than the PCC-CTMP fractions, although the fines content of the unfractionated PCC-CTMP was larger than that of the CTMP. The fiber length, fiber width and shape factor distributions of the fractions were essentially unaf- fected by the precipitation process, as the fines were not included in the distributions. This is illustrated in Figs. 5 and 6, which show the length and width distributions, respectively, in fractions of samples refined for 30 min.
0
R30
R100
R200
R400
Fig. 3 Cumulative residuals on the wires, calculated by weight. The ‘pass’ fraction has been excluded to facilitate the comparison
0 min (of tot. ash) 0 min (ash cont.)
30 min (of tot. ash) 30 min (ash cont.)
60 min (of tot. ash) 60 min (ash cont.)
7
70
6
60
5
50
4
40
3
30
2
20
1
10
0
0
R30 R100 R200 R400
Fig. 4 Ash distribution in the fiber fractions. The bars (indicated on the left-hand ordinate, ‘‘Of tot ash in composite’’) show the percentage of ash in the fractions of the unrefined and refined PCC-CTMP fillers after fractionation. The lines (indicated on the right-hand ordinate, ‘‘Ash content of fraction’’) show the ash content in each fraction
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