The evaluation of ceramic dispersions using analytical centrifugation (STEPTechnology), combined with multisample analytical centrifugation is described
[134]. The shear-dependent sedimentation rate, consolidation, and packing behavior
are directly analyzed. In addition, the particle size distribution can be obtained with
high resolution. Application studies on kaolin, silicon carbide, and silica dispersions
show the high potential of this method. The potential of multisample analytical
centrifugation for formulation design (stability as well as flocculation) was demonstrated in investigations on the effect of particle (silica, calcium carbonate) and
polymer (PAA) concentration on dispersion properties of different stabilized
suspensions [135].
The dispersibility of carbon nanotubes (CNTs) was assessed by studying the
sedimentation of CNTs dispersed in aqueous surfactant solutions at different
ultrasonication treatment times using a LUMiSizer. Different commercially available
multiwalled CNTs, such as Baytubes C150P or Nanocyl NC7000, showing quite
different kinetics, were compared. In addition, the particle size distributions were
analyzed using dynamic light scattering and centrifugal separation analysis [136].
As described, the application of flocculants with two or more components is of
growing importance for solid–liquid separation processes, including the dewatering
of ultrafine materials (sludge from clay, coal, or gravel pits) or sewage sludge.
Through various examples involving the preparation of well-characterized model
systems, it has been demonstrated that the removal of detrimental substances
such as colored materials (dyes) or stickies is favorable by the formation of
PECs. In addition, PECs as well as PSCs can be used as materials for the sorption
of hydrophobic materials such as organic compounds.
5.2 Use of Natural Polymers
For many years, in most cases synthetic polyelectrolytes such as PDADMAC or
PEI as PC, and PAC, PAMPS, or PSS as PA were used for complex formation. But
at present, the application of so-called natural polymers is of growing importance in
the field of complex formation. Natural polymers occur in nature and can be
extracted. Examples are chitosan as well as polysaccharides such as starch, pectin,
or alginate. Natural polymers are used because of their good biodegradability and
high biocompatibility in a wide range of applications in industry. They can have
cationic charge (chitosan) [137] or can be modified with cationic as well as hydrophobic units [74].
The interaction between modified starch and sticky-containing wastewater was
mentioned in Sect. 3.2. of this article [67, 68]. Mihai [141] investigated chitosanbased nonstoichiometric PECs (NPECs) as specialized flocculants. Such NPEC
were more effective than chitosan in kaolin separation. Their main advantage is the
increase in critical concentration for kaolin restabilization. The NPEC particles
were adsorbed on the kaolin surface, protecting them more efficiently against
re-dispersion.
Polyelectrolyte Complexes in Flocculation Applications
57
[134]. The shear-dependent sedimentation rate, consolidation, and packing behavior
are directly analyzed. In addition, the particle size distribution can be obtained with
high resolution. Application studies on kaolin, silicon carbide, and silica dispersions
show the high potential of this method. The potential of multisample analytical
centrifugation for formulation design (stability as well as flocculation) was demonstrated in investigations on the effect of particle (silica, calcium carbonate) and
polymer (PAA) concentration on dispersion properties of different stabilized
suspensions [135].
The dispersibility of carbon nanotubes (CNTs) was assessed by studying the
sedimentation of CNTs dispersed in aqueous surfactant solutions at different
ultrasonication treatment times using a LUMiSizer. Different commercially available
multiwalled CNTs, such as Baytubes C150P or Nanocyl NC7000, showing quite
different kinetics, were compared. In addition, the particle size distributions were
analyzed using dynamic light scattering and centrifugal separation analysis [136].
As described, the application of flocculants with two or more components is of
growing importance for solid–liquid separation processes, including the dewatering
of ultrafine materials (sludge from clay, coal, or gravel pits) or sewage sludge.
Through various examples involving the preparation of well-characterized model
systems, it has been demonstrated that the removal of detrimental substances
such as colored materials (dyes) or stickies is favorable by the formation of
PECs. In addition, PECs as well as PSCs can be used as materials for the sorption
of hydrophobic materials such as organic compounds.
5.2 Use of Natural Polymers
For many years, in most cases synthetic polyelectrolytes such as PDADMAC or
PEI as PC, and PAC, PAMPS, or PSS as PA were used for complex formation. But
at present, the application of so-called natural polymers is of growing importance in
the field of complex formation. Natural polymers occur in nature and can be
extracted. Examples are chitosan as well as polysaccharides such as starch, pectin,
or alginate. Natural polymers are used because of their good biodegradability and
high biocompatibility in a wide range of applications in industry. They can have
cationic charge (chitosan) [137] or can be modified with cationic as well as hydrophobic units [74].
The interaction between modified starch and sticky-containing wastewater was
mentioned in Sect. 3.2. of this article [67, 68]. Mihai [141] investigated chitosanbased nonstoichiometric PECs (NPECs) as specialized flocculants. Such NPEC
were more effective than chitosan in kaolin separation. Their main advantage is the
increase in critical concentration for kaolin restabilization. The NPEC particles
were adsorbed on the kaolin surface, protecting them more efficiently against
re-dispersion.
Polyelectrolyte Complexes in Flocculation Applications
57