two sub-processes have already been discussed (formation by Petzold and Schwartz
[52] and adsorption in Sect. 2) and will hence not be further discussed here.
The interaction between pre-formed PECs and pulp fibres has been systematically studied by several research teams, and the use of pre-formed PECs in
papermaking has been demonstrated to significantly enhance the physical
properties of paper. The PECs tested were combinations of PAA and PAH or of
PAE and CMC [19, 53, 54]. An undesired densification occurred when the PECs
were added to the various tested pulps, but this effect was not as pronounced as that
achieved by mechanical beating, indicating the great potential for using PECs to
enhance paper strength while maintaining a significant part of the paper bulk, as can
be seen in Figs. 9 and 10 [54]. In another study, paper strength was reported to
120
Hardwood ref
Hardwood Ref
Hardwood PAE
BCTMP Ref
BCTMP PAE
BCTMP PEC/PAE
Softwood Ref
Softwood PAE
Softwood PEC/PAE
Hardwood PEC/PAE
Hardwood PAE
BCTMP ref
Softwood ref
Softwood PAE
Softwood PEC/PAE
BCTMP PAE
BCTMP PEC/PAE
Hardwood PEC/PAE
100
80
60
Tensile index (kNm/kg)
Bending Stiffness (Nm)
40
20
0
450
500
550
600
650
Density (kg/m
3
)
700
750
800
0
0.0013
0.0012
0.0011
0.001
0.0009
0.0008
0.0007
0.0006
0.0005
0.0004
20
40
60
Tensile Index (kNm/kg)
80
100
120
a
b
Fig. 10 The relationship between (a) tensile index, i.e. the stress at break, and sheet density and
(b) bending stiffness and tensile index for all the pulps studied in Ga ¨rdlund et al. [54]
100
90
80
70
60
50
Tensile index (kNm/kg)
40
30
20
10
0
0
50
100
Beating energy (kWh/t)
150
200
Reference
PAE
PEC/PAE
250
Fig. 9 Tensile index, i.e. the stress at break of paper sheets from HBK fibres subjected to
chemical treatment (PAE or PAE/PEC), mechanical beating or a combination of both. From
Ga ¨rdlund et al. [54]
14
C. Ankerfors and L. Wa ˚gberg
[52] and adsorption in Sect. 2) and will hence not be further discussed here.
The interaction between pre-formed PECs and pulp fibres has been systematically studied by several research teams, and the use of pre-formed PECs in
papermaking has been demonstrated to significantly enhance the physical
properties of paper. The PECs tested were combinations of PAA and PAH or of
PAE and CMC [19, 53, 54]. An undesired densification occurred when the PECs
were added to the various tested pulps, but this effect was not as pronounced as that
achieved by mechanical beating, indicating the great potential for using PECs to
enhance paper strength while maintaining a significant part of the paper bulk, as can
be seen in Figs. 9 and 10 [54]. In another study, paper strength was reported to
120
Hardwood ref
Hardwood Ref
Hardwood PAE
BCTMP Ref
BCTMP PAE
BCTMP PEC/PAE
Softwood Ref
Softwood PAE
Softwood PEC/PAE
Hardwood PEC/PAE
Hardwood PAE
BCTMP ref
Softwood ref
Softwood PAE
Softwood PEC/PAE
BCTMP PAE
BCTMP PEC/PAE
Hardwood PEC/PAE
100
80
60
Tensile index (kNm/kg)
Bending Stiffness (Nm)
40
20
0
450
500
550
600
650
Density (kg/m
3
)
700
750
800
0
0.0013
0.0012
0.0011
0.001
0.0009
0.0008
0.0007
0.0006
0.0005
0.0004
20
40
60
Tensile Index (kNm/kg)
80
100
120
a
b
Fig. 10 The relationship between (a) tensile index, i.e. the stress at break, and sheet density and
(b) bending stiffness and tensile index for all the pulps studied in Ga ¨rdlund et al. [54]
100
90
80
70
60
50
Tensile index (kNm/kg)
40
30
20
10
0
0
50
100
Beating energy (kWh/t)
150
200
Reference
PAE
PEC/PAE
250
Fig. 9 Tensile index, i.e. the stress at break of paper sheets from HBK fibres subjected to
chemical treatment (PAE or PAE/PEC), mechanical beating or a combination of both. From
Ga ¨rdlund et al. [54]
14
C. Ankerfors and L. Wa ˚gberg