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Cellulose (2021) 28:5807–5826
CTMP
PCC-CTMP
CTMP (0 min) CTMP (30 min) CTMP (60 min)
PCC-CTMP (0 min) PCC-CTMP (30 min) PCC-CTMP (60 min)
0 100 200 300 400 500
5
4
3
2
1
0
0 min
30 min
60 min
R30 R100 R200 R400
n/f CTMP
Fig. 10 Densities of the CTMP and PCC-CTMP sheets. n/f = not fractionated
Fig. 12 Tensile stiffness indexes of the CTMP and PCC-CTMP sheets. The category n/f refers to the sheets made using unfractionated pulp. Tensile stiffness indexes of unfractionated PCC-CTMP sheets were below test limit
CTMP (0 min) CTMP (30 min) CTMP (60 min)
PCC-CTMP (0 min) PCC-CTMP (30 min) PCC-CTMP (60 min)
40
CTMP (0 min) CTMP (30 min)
PCC-CTMP (0 min) PCC-CTMP (30 min) CTMP (60 min)
30
PCC-CTMP (60 min)
2.5
20
2.0
10
1.5
1.0
0
R30 R100 R200 R400
n/f CTMP
0.5
Fig. 11 Tensile index of CTMP and PCC-CTMP sheets. n/f = not fractionated. The tensile indexes of unfractionated PCC-CTMP sheets were below the test limit
0.0
R30 R100 R200 R400 n/f CTMP
Fig. 13 Elastic moduli of the CTMP and PCC-CTMP sheets. n/f = not fractionated. The elastic moduli of unfractionated PCC-CTMP sheets were below the test limit
sheets was therefore mainly due to the presence of the mineral-rich ‘pass’ fraction.
which fines have physical and chemical properties different from those of the coarse fraction. Refining introduces changes, including fiber damage and removal of the fiber layer and the formation of debris. Calcium carbonate precipitation onto the fibers can be affected by refining. PCC was found to be more prone to attach to the fiber parts where the outer layer ( P 1) had been removed or damaged, and SEM images showed that a prolonged refining and formation of higher content of split fibers means that PCC can be found on the inner lumen wall, despite the fact that the outer layers of CTMP fibers (primary wall and
Discussion
Effect of CTMP refining on the in-situ precipitation of calcium carbonate
The current work confirms that mechanical refining changes the precipitation efficiency and thus the composition and properties of the PCC-fiber compos- ite. The CTMP has a large particle size distribution in
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