as flocculant systems, produces synergistic effects on the flocculation. Many different
systems have been applied, especially in the paper industry.
The so-called dual system was first described in literature in the 1970s and
consists of two oppositely charged polymers. It can produce distinct improvements
in retention and dewatering [5, 6]. From the 1980s until now, much work has been
done to improve our knowledge about such systems. This has been especially true
in research areas like paper forming and floc shear stability. A special type of dual
system, the so-called microparticle containing system, has been developed. In this
system, the addition of a cationic polymer is followed by the addition of an anionic
submicron particle suspension. Examples of this type of retention aid system are
cationic starch used in conjunction with anionic colloidal silica or anionic colloidal
alumina hydroxide and cationic copolymers of acrylamide used together with
sodium montmorrilonite. Several systems of this type are commercially available.
They are said to be very efficient flocculants, which give smaller flocs at an equal
degree of flocculation compared to single-component systems.
Very good reviews, which include a survey of some aggregation mechanisms
and comparisons between different dual systems, are available [7–12].
This chapter focuses on polymer–polymer systems, mainly in the paper industry.
But, current approaches used in other fields of flocculation will also be mentioned.
2.1 Interaction with Cellulose (Paper Industry)
An example of an early and very detailed investigation of such a dual system is the
work of Moore [13], in which different types of cationic polymers were combined
with hydrolyzed polyacrylamides at various alumina concentrations. In contrast to
other workers, Moore studied the charge relationship of the various charged
species. He discovered that a combination of cationic and anionic polymers can
give very high levels of retention with high shear resistance only in the case of a
proper balance of charges and concentrations.
Mu ¨ller and Beck [14] have investigated cationic polyethylene imine (PEI) or
polyamidoamine in combination with an anionic polyacrylamide. They explained
that under conditions of optimum performance, two mechanisms are operating:
charge patch formation and bridging. The relatively short-chain PC produces a very
fine flocculation of the particles via a charge patch destabilization mechanism. If a
long-chain polyacrylamide (PAA) is then added to the stock, the negatively charged
chains “get a good grip” on the positive patches of the primary floc and bring further
linkages by forming bridges. Other aspects of the floc formation mechanism were
studied by Peta ¨ja ¨ [15], including the influence of the type and amount of PC, the
time delay between cationic and anionic addition, and the degree of turbulence. It
was shown that the agitation level and control of floc formation after cation addition
are very important for good sheet formation.
In Table 1, a wide variety of examples of polymer–polymer systems from the
literature are listed. The most commonly used systems are those in which the PC is
added prior to a high molar mass PA. It was confirmed by different authors that the
32
G. Petzold and S. Schwarz
systems have been applied, especially in the paper industry.
The so-called dual system was first described in literature in the 1970s and
consists of two oppositely charged polymers. It can produce distinct improvements
in retention and dewatering [5, 6]. From the 1980s until now, much work has been
done to improve our knowledge about such systems. This has been especially true
in research areas like paper forming and floc shear stability. A special type of dual
system, the so-called microparticle containing system, has been developed. In this
system, the addition of a cationic polymer is followed by the addition of an anionic
submicron particle suspension. Examples of this type of retention aid system are
cationic starch used in conjunction with anionic colloidal silica or anionic colloidal
alumina hydroxide and cationic copolymers of acrylamide used together with
sodium montmorrilonite. Several systems of this type are commercially available.
They are said to be very efficient flocculants, which give smaller flocs at an equal
degree of flocculation compared to single-component systems.
Very good reviews, which include a survey of some aggregation mechanisms
and comparisons between different dual systems, are available [7–12].
This chapter focuses on polymer–polymer systems, mainly in the paper industry.
But, current approaches used in other fields of flocculation will also be mentioned.
2.1 Interaction with Cellulose (Paper Industry)
An example of an early and very detailed investigation of such a dual system is the
work of Moore [13], in which different types of cationic polymers were combined
with hydrolyzed polyacrylamides at various alumina concentrations. In contrast to
other workers, Moore studied the charge relationship of the various charged
species. He discovered that a combination of cationic and anionic polymers can
give very high levels of retention with high shear resistance only in the case of a
proper balance of charges and concentrations.
Mu ¨ller and Beck [14] have investigated cationic polyethylene imine (PEI) or
polyamidoamine in combination with an anionic polyacrylamide. They explained
that under conditions of optimum performance, two mechanisms are operating:
charge patch formation and bridging. The relatively short-chain PC produces a very
fine flocculation of the particles via a charge patch destabilization mechanism. If a
long-chain polyacrylamide (PAA) is then added to the stock, the negatively charged
chains “get a good grip” on the positive patches of the primary floc and bring further
linkages by forming bridges. Other aspects of the floc formation mechanism were
studied by Peta ¨ja ¨ [15], including the influence of the type and amount of PC, the
time delay between cationic and anionic addition, and the degree of turbulence. It
was shown that the agitation level and control of floc formation after cation addition
are very important for good sheet formation.
In Table 1, a wide variety of examples of polymer–polymer systems from the
literature are listed. The most commonly used systems are those in which the PC is
added prior to a high molar mass PA. It was confirmed by different authors that the
32
G. Petzold and S. Schwarz