in ash content of the specimen from 525 °C to 900 °C (Table 6 ). Fillerretention values as a function of PAM pretreatment and filler contents were determined and they are shown in Table 6 as well. Effects of accelerated ageing The acidity–alkalinity of the handsheets, measured as pH, i. e. a measure of the potential activity of hydrogen ions, is affected by many other factors, including organic components of specimens and accelerated ageing conditions. As a result of ageing effect and the corresponding pH values of handsheets are given in Table 7 . Table 6
unmodified PCC. In the
present work these increments were of 8%, 8% and 6%,
respectively. Contrary to the aforementioned published
results the bulk did not vary when using the modified
filler, which is a positive achievement.
Three different pilot trials were conducted and papers
with different densities were produced. The filler content
obtained in these trials was in general smaller than that
obtained in the laboratory experiments, the latter with
fillerretention values always superior to 93% (Table 1).
These differences are due to the distinct operating
strength than those produced with unmodified PCC,
while the optical properties are not significantly affected,
at filler levels ranging from about 5 to 25% (Zhao et al.
2005). Laleg et al. (2008) treated PCC particles with
anionic polymer dispersions (latex) and found that the
resultant slurries could improve paper internal resistance
Nordic Pulp & Paper Research Journal Vol 29 no (2) 2014
and breaking length for filler levels in the handsheets in
the range of 10 to 25%, besides improving fillerretention, sizing performance
effect of water quality on 2: 134
Hartler, N. washing of unbleached kraft pulps
McKague, A . B. Reactions of lignin model dimers 2:84
Kang, G. with chlorine dioxide
Reeve, D. W.
Middleton, S. R. Fillerretention and the specific sur- 3: 156
Scallan, A . M. face area of fibers
Milanova, E. On the determination of residual 1:4
Dorris, G. M. alkali in black liquors
Norden, H. K Cake filtration with application to 4:208
Kauppinen, P. dewatering of pulp
Nordstrom, B. Influence of sheet anisotropy, 1 :53
Norman, B. formation, Z-toughness and tensile
(Vicron-type) and precipitated cal-
cium carbonate were used. A series of reference
sheets and a series of sheets containing 4.2% cationic
starch (CS) were made. Starch retention was aided by
the addition of 0.3% anionic polyacrylamide (A-
PAM) to ensure that CS which was not adsorbed
onto the fibers and fillers in the stock was precipitat-
ed onto the stock components in the form of a
polyelectrolyte complex (6). By using such a dual
retention aid system a high fillerretention (> 90%) is
Two series of reference sheets without CS were
the CPPA Technical Section.
To ensure a reproducible level of fillerretention in
the handsheets a method based on previous work was
used for filler addition (16).
Cont. p. 29
Nordic Pulp and Paper Research Journal no. 111 992
sequential addition, (DC), where acidification was
Oxygen bleaching was performed in a 50 1 auto-
clave equipped with a stirring mechanism.
Chlorine dioxide treatment at 3.5% consistency
was carried out in the ozone reactor. Temperature
was 20°C. When other consistencies were used, the
water consistency, turbidity, and cationic
demand were all significantly affected by the enzyme
dosing strategy. A significantly increased level of
turbidity, indicating a greater amount of non-retained
dissolved and colloidal substances, was seen, in particular
for the sample refined during the enzymatic hydrolysis
without the following deactivation step.
The data for the first pass and fillerretention, as well as
the retention levels of AKD and starch, determined from
their concentrations in the headbox stock and white water
samples (Table 5), show that
correlation has been found between the reduction in
strength at a certain filler content and the amount of
filler retained in the sheet at a certain charge of filler,
Fig. 10. The responses to filler addition of the papers
containing different mechanical pulps differ some-
what. The values plotted have been normalized to a
reference level of 20 % filler. The fact that these
differences correlate with fillerretention suggests that
the reason for these differences is probably experi-
mental and not a result of the character of
pigments do not have any
appreciable bonding capability to cellulosic fibers.
Several methods for enhancing the bonding capacity of
fillers with fibers have been proposed to help improve
paper strength and allow for higher filler contents.
Natural polymers and their derivatives, such as starch,
cellulose, carboxymethylcellulose (CMC), chitin and
guar gum, have been examined for improving filler
bondability, paper strength or fillerretention (Shen et al.
Starch is widely used by several industries, such as
adhesives and paper. The benefits of starch
disturb the fibre-
fibre and fibre-fillerretention by interfering with add-
ed cationic chemicals. The formation of different kinds
of polyelectrolyte complexes (Dickinson, Eriksson
1990; Lindstrom 1989), are examples of interfering re-
actions which may be detrimental to paper production.
If the degree of closure of the system is high, deposits
forming on rolls and wires may also cause severe dis-
turbances in paper machine runability.
The anionic character of the detrimental substances
is due to dissociated acidic groups such as carboxyl and