Those interactions are very important in the paper industry [50, 51] because the
effectiveness of cationic polymers as retention and drainage aids in the manufacture
of paper is strongly affected and sometimes even limited by anionic macromolecules, which dissolve in the white water. Such polymers are, for example, lignin
or carbohydrates from wood. Therefore, the application-relevant effect of pine xylan
on the use of PEI, and acrylamide copolymer as retention and drainage aid, for an
unbleached sulfite pulp was investigated [50]. The formation of PECs between pine
xylan and three cationic polymers has been studied as a function of pH and ionic
strength [51]. Complex formation was found to be nonstoichiometric and both
soluble and insoluble complexes are formed, with maximum precipitation occurring
when the complexes are neutral. A tentative structure of the complexes was
suggested.
3.1 Paper Recycling
The problems of complex formation are growing because the increasing use of
de-inked pulps, in combination with the closure of paper machine circuits in pulp
and paper industry processes, is leading to an accumulation of so-called trash
material or tacky substances. The formation of a high amount of these substances
affects paper production negatively due to lower retention of the filler or increased
deposition on paper machines. These substances are brought into the process
through many different sources. The recycling of paper is one of the most important
ways of producing paper.
The variety of tacky materials present in papermaking systems have different
names: for instance, the accumulated pollutants in the water recycling system are
called dissolved and colloidal substances (DCS). The composition of DCS, which
mainly come from pulp, filler, recycled water, and the chemicals added during the
papermaking process, is very complex.
Pelton [40] describes PEC formation as an important part of paper technology.
One example is the strategy for removing the anionic PEL components of the DCS
by adding oppositely charged polymers to form PEC. Oppositely charged PEL will
form complexes over a broad range of stoichiometric ratios. However, the
complexes tend to be water-soluble unless they are nearly stoichiometric because
an excess of either positive or negative particle charge will confer water solubility.
This behavior is illustrated by the interaction of PDADMAC, a linear cationic PEL,
with kraft lignin, which is a branched anionic phenolic polymer resulting from the
decomposition of lignin in the kraft pulping process. The formation and the amount
of precipitated kraft-lignin–PDADMAC complex were investigated as a function of
the mass ratio (kraft lignin/PDADMAC) and the pH [40]. But, kraft lignin is not
ideally suited for fundamental studies of PEC formation because lignin is a polydisperse polymer with a complicated structure; hence, most of the basic information
about PEC comes from investigations on well-defined synthetic polymers [52] (see
Sect. 4).
Polyelectrolyte Complexes in Flocculation Applications
41
effectiveness of cationic polymers as retention and drainage aids in the manufacture
of paper is strongly affected and sometimes even limited by anionic macromolecules, which dissolve in the white water. Such polymers are, for example, lignin
or carbohydrates from wood. Therefore, the application-relevant effect of pine xylan
on the use of PEI, and acrylamide copolymer as retention and drainage aid, for an
unbleached sulfite pulp was investigated [50]. The formation of PECs between pine
xylan and three cationic polymers has been studied as a function of pH and ionic
strength [51]. Complex formation was found to be nonstoichiometric and both
soluble and insoluble complexes are formed, with maximum precipitation occurring
when the complexes are neutral. A tentative structure of the complexes was
suggested.
3.1 Paper Recycling
The problems of complex formation are growing because the increasing use of
de-inked pulps, in combination with the closure of paper machine circuits in pulp
and paper industry processes, is leading to an accumulation of so-called trash
material or tacky substances. The formation of a high amount of these substances
affects paper production negatively due to lower retention of the filler or increased
deposition on paper machines. These substances are brought into the process
through many different sources. The recycling of paper is one of the most important
ways of producing paper.
The variety of tacky materials present in papermaking systems have different
names: for instance, the accumulated pollutants in the water recycling system are
called dissolved and colloidal substances (DCS). The composition of DCS, which
mainly come from pulp, filler, recycled water, and the chemicals added during the
papermaking process, is very complex.
Pelton [40] describes PEC formation as an important part of paper technology.
One example is the strategy for removing the anionic PEL components of the DCS
by adding oppositely charged polymers to form PEC. Oppositely charged PEL will
form complexes over a broad range of stoichiometric ratios. However, the
complexes tend to be water-soluble unless they are nearly stoichiometric because
an excess of either positive or negative particle charge will confer water solubility.
This behavior is illustrated by the interaction of PDADMAC, a linear cationic PEL,
with kraft lignin, which is a branched anionic phenolic polymer resulting from the
decomposition of lignin in the kraft pulping process. The formation and the amount
of precipitated kraft-lignin–PDADMAC complex were investigated as a function of
the mass ratio (kraft lignin/PDADMAC) and the pH [40]. But, kraft lignin is not
ideally suited for fundamental studies of PEC formation because lignin is a polydisperse polymer with a complicated structure; hence, most of the basic information
about PEC comes from investigations on well-defined synthetic polymers [52] (see
Sect. 4).
Polyelectrolyte Complexes in Flocculation Applications
41