chloride (PTMMAC) and 5% CMC were added to cellulose slurries, approximately
94% of the polymers were retained in the sheets by formation of a polyion complex.
PEC dispersions have been used as a fixing agent, flocculant, or retention aid to
increase the water resistance of paper [87].
Detailed studies of particle (silica) flocculation using pre-mixed complexes were
done by Buchhammer [88], Schwarz and Dragan [89], and Mende et al. [90, 91].
The flocculation efficiency of some nonstoichiometric interpolyelectrolyte complex dispersions synthesized by the interaction between poly(sodium 2-acrylamido-2methylpropanesulfonate) (NaPAMPS) and three strong PCs bearing quaternary
ammonium salt centers in the backbone on a stable monodisperse silica dispersion
have been tested. The PCs PDADMAC and PCA5 alone showed a very narrow range
of flocculation. In the case of the most hydrophobic PC, PCA5D1, the window of
optimum flocculation concentration was broader compared with other PCs [88].
Mende investigated the flocculation of silica dispersions in dependence of the
properties of nonstoichiometric PECs with different charge excess and hydrophobicity
as well as different average hydrodynamic particle size. PDADMAC as PC and
different PAs such as poly(styrene-p-sodium sulfonate) (NaPSS) and poly(acrylamide-co-sodium acrylate), were used so that PECs with different charge excess and
hydrophobicity as well as different average hydrodynamic particle size could be
prepared. The work was focused especially on the stability of complexes and it was
pointed out that a higher tendency to instability results for complexes with PAs that
have a Π-system (phenyl-) in the polymer chain [94]. The average hydrodynamic
particle size and the polydispersity indices (PI), determined by dynamic light scattering were strongly influenced by the mixing conditions of the PECs and the nature of
the used polyelectrolytes. It was found that particles with narrow or monodisperse
distribution can be prepared under the condition that the PC is the starting solution,
as shown in Fig. 11. Dispersions with PI values between 0.03 and 0.06 are described as
monodisperse, whereas a narrow particle size distribution is found at PI values
between 0.1 and 0.2. A broad particle size distribution is represented by PI values
between 0.25 and 0.5; at PI > 0.5 the result is not analyzable [89].
The reaction process between silica and the used flocculants can be divided into
three intervals (destabilization, flocculation optimum, and restabilization) as known
for all other polymer flocculants. For an effective flocculation of a charged substrate,
both electrostatic as well as hydrophobic interactions play an important role. The
interval up to the beginning of the flocculation optimum is mainly influenced by
electrostatic interactions (the charge density of the flocculant) but the broadness of
the flocculation optimum depends largely on hydrophobic interactions. Hydrophobic interactions also play an important role in the shear stability of the formed flocs.
As shown in Fig. 12, the floc size rapidly increases in dependence of flocculant
charge added to the silica dispersions. The size of flocs obtained with complexes is
larger than the size of flocs obtained with the pure PC. The monomodal particle size
distribution for the silica dispersion (n ¼ 0) changes to bimodal or multimodal under
the influence of the amount of cationic charge. With increasing amount of cationic
charge, the volume proportion of single silica particles decreases and the fraction of
bigger aggregates increases (Fig. 12a). The beginning of the flocculation optimum
50
G. Petzold and S. Schwarz
94% of the polymers were retained in the sheets by formation of a polyion complex.
PEC dispersions have been used as a fixing agent, flocculant, or retention aid to
increase the water resistance of paper [87].
Detailed studies of particle (silica) flocculation using pre-mixed complexes were
done by Buchhammer [88], Schwarz and Dragan [89], and Mende et al. [90, 91].
The flocculation efficiency of some nonstoichiometric interpolyelectrolyte complex dispersions synthesized by the interaction between poly(sodium 2-acrylamido-2methylpropanesulfonate) (NaPAMPS) and three strong PCs bearing quaternary
ammonium salt centers in the backbone on a stable monodisperse silica dispersion
have been tested. The PCs PDADMAC and PCA5 alone showed a very narrow range
of flocculation. In the case of the most hydrophobic PC, PCA5D1, the window of
optimum flocculation concentration was broader compared with other PCs [88].
Mende investigated the flocculation of silica dispersions in dependence of the
properties of nonstoichiometric PECs with different charge excess and hydrophobicity
as well as different average hydrodynamic particle size. PDADMAC as PC and
different PAs such as poly(styrene-p-sodium sulfonate) (NaPSS) and poly(acrylamide-co-sodium acrylate), were used so that PECs with different charge excess and
hydrophobicity as well as different average hydrodynamic particle size could be
prepared. The work was focused especially on the stability of complexes and it was
pointed out that a higher tendency to instability results for complexes with PAs that
have a Π-system (phenyl-) in the polymer chain [94]. The average hydrodynamic
particle size and the polydispersity indices (PI), determined by dynamic light scattering were strongly influenced by the mixing conditions of the PECs and the nature of
the used polyelectrolytes. It was found that particles with narrow or monodisperse
distribution can be prepared under the condition that the PC is the starting solution,
as shown in Fig. 11. Dispersions with PI values between 0.03 and 0.06 are described as
monodisperse, whereas a narrow particle size distribution is found at PI values
between 0.1 and 0.2. A broad particle size distribution is represented by PI values
between 0.25 and 0.5; at PI > 0.5 the result is not analyzable [89].
The reaction process between silica and the used flocculants can be divided into
three intervals (destabilization, flocculation optimum, and restabilization) as known
for all other polymer flocculants. For an effective flocculation of a charged substrate,
both electrostatic as well as hydrophobic interactions play an important role. The
interval up to the beginning of the flocculation optimum is mainly influenced by
electrostatic interactions (the charge density of the flocculant) but the broadness of
the flocculation optimum depends largely on hydrophobic interactions. Hydrophobic interactions also play an important role in the shear stability of the formed flocs.
As shown in Fig. 12, the floc size rapidly increases in dependence of flocculant
charge added to the silica dispersions. The size of flocs obtained with complexes is
larger than the size of flocs obtained with the pure PC. The monomodal particle size
distribution for the silica dispersion (n ¼ 0) changes to bimodal or multimodal under
the influence of the amount of cationic charge. With increasing amount of cationic
charge, the volume proportion of single silica particles decreases and the fraction of
bigger aggregates increases (Fig. 12a). The beginning of the flocculation optimum
50
G. Petzold and S. Schwarz