Use of Cationic Polyelectrolytes for the Fixation of Anionic Trash onto Silica Particles A. GUYARD, B. CHABOT and C. DANEAULT
Cationic polyelectrolytes used as retention aids are affected by the anionic trash found in white waters. This leads to a reduction of their efficiency and to the formation of polymeric complexes that can precipitate into sticky deposits. Various chemicals are used to neutralize these detrimental substances. However, with the increasing closure of the water loops, new approaches will be required to provide effective control of anionic trash levels in process waters. Adsorption of detrimental substances onto modified colloidal silica nanoparticles has been studied to eliminate them from process waters. Results show that cationized silica improved the removal of detrimental substances. Adsorption was dependent on the type of polymer used to modify the silica and on the cationization level carried out on the silica nanoparticles. Les polyélectrolytes cationiques utilisés comme agents de rétention sont affectés par les déchets anioniques présents dans les eaux blanches. Leur présence tend à réduire leur efficacité et à former des complexes polymériques pouvant précipiter sous forme de dépôts collants. Divers produits chimiques sont généralement utilisés pour neutraliser ces substances nuisibles. Cependant, avec la fermeture progressive des circuits d'eau, de nouvelles approches doivent être envisagées pour permettre un contrôle efficace du taux de déchets anioniques dans les eaux du procédé. L'adsorption de substances nuisibles sur des nanoparticules de silices colloïdales modifiées a été étudiée en vue de leur élimination des circuits d'eaux du procédé. Les résultats montrent que l’emploi de silices cationiques améliore l’élimination des substances nuisibles. L'adsorption dépend du type de polymère utilisé pour modifier la silice et du niveau de cationisation résultant de cette modification.
INTRODUCTION The white water produced during papermaking consists of various constituents such as fibres, fines, mineral fillers, various chemical additives, as well as dissolved and colloidal substances (DCS), which are generated during pulping and bleaching operations, or result from deinked pulp [1]. The DCS include a large variety of substances [2], such as fatty acids, resin acids or sterols, and includes wood polymers, such as polysaccharides, lignin or pectin. Some of these substances are responsible for the formation of sticky deposits that can affect paper machine runnability and paper quality significantly [3]. Part of the wood extractives tends to adsorb onto fines, reducing their binding power and paper-strength properties [4]. These substances also interact strongly with cationic polymers, used as retention or drainage aids, producing polymeric complexes that A. Guyard, B. Chabot and C. Daneault Univ. Québec Trois-Rivières Centre intégré en pâtes et papiers CP 500 3351 boul. des Forges Trois-Rivières, QC G9A 5H7 Canada
can be responsible for pitch deposition on paper machine parts (fabrics, rolls, felts). The anionic trash also affects the ionic balance by increasing the cationic polymer consumption. These detrimental effects are also responsible for higher effluent loads and increased production costs. For environmental reasons, paper mills must actually reduce fresh water consumption, by closing their white water systems. However, this leads to an excessive buildup of DCS in process waters, leading to serious production problems, as discussed above. Various chemicals are used to neutralize DCS to inhibit their negative impacts on papermaking operations. Generally, this is accomplished following a three-stage process: neutralization of the anionic charge; precipitation of polymer complexes; and fixation of the complex onto fibres [5]. Most of the studies carried out to control DCS have attempted to fix these neutralized complexes onto fibres to clean the white water by their elimination with the paper produced, with possible detrimental effects on paper quality. Cationic polymers are generally used to control DCS [6]. The mode of interaction with the anionic trash depends strongly on their charge density and their molecular weights [7].
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Cationic polymers with high molecular weights and low charge densities, such as cationic polyacrylamides (C-PAM), are used commonly for flocculation by a bridging mechanism [8], while polymers with low molecular weights and high charge densities, such as poly-diallyldimethylammonium chlorides (pDADMAC) are used to neutralize detrimental substances through patch flocculation or charge neutralization mechanisms [9,10]. The aim of this study is to develop an effective methodology to remove DCS from white water by their selective adsorption onto modified silica particles. This work is directed to understand better how commercial cationic polymers, such as p-DADMAC and C-PAM, affect the deposition mechanism of DCS onto silica particles.
EXPERIMENTAL Materials The nanometric silica Ludox TM 50 was purchased from Fluka (Buchs, Switzerland) (7631-86-9) no. 420778. It has a specific surface area of 140 m²/g and a density of 1.4 g/cm³ at 25°C. Various diluted silica dispersions at 1% concentration by weight were prepared by 9
diluting the commercial solution (50% by weight) with distilled water. The pH was adjusted using HCl 0.1 mol/L or NaOH 0.1 mol/ L solutions. The salt concentration was also adjusted with NaCl. P-DADMAC was purchased from Aldrich (26062-79-3). It has a density of 1.04 g/mL at 25°C, a charge density of 5.1 meq/g, and a molecular weight (average) of 4.4 x 105 g/mol. The molecular weight was determined by gel permeation chromatography (GPC) according to the procedure described in [11]. The charge density was independent of pH. The C-PAM was supplied by Ciba Speciality Chemicals, Basel, Switzerland. It has a molecular weight (average) of 3 x 106 g/mol determined using the same GPC technique. Its charge density was 1.17 meq/g at pH 4.5 and 0.81 meq/g at pH 6.5. The C-PAM charge density was pH dependent, since the ester group of the aminoethyl acrylate copolymer is hydrolyzed at pHs higher than 6. Thus, it leads to a lower charge density at pH 6.5. To help identify the adsorption mechanism on modified silica particles, a model compound was selected for the experiments. Polygalacturonic acid (PGA) has been identified as one of the main components of the anionic trash in bleached thermomechanical pulps [12]. The PGA was purchased from Fluka (25990-10-7). The molecular weight was ~25 000 g/mol. Solutions at 1 g/L (1000 ppm) were prepared by solubilization in a 0.1 mol/L caustic solution for 24 h and then the pH was adjusted using 0.1 mol/L HCl. Its charge density was 4.5 meq/g at pH 4.5 and 6.3 meq/g at pH 6.5.
Methodology Adsorption Isotherms Adsorption isotherms of cationic polymer on the surface of the silica particles were measured at room temperature (25°C). The pHs of polymer solutions and colloidal silica dispersions were adjusted to pH 4.5 and 6.5, re-
spectively, using 0.1 mol/L HCl or NaOH solutions. The ionic strength of all solutions was adjusted to the required level using NaCl solutions. Silica dispersions, considered here as the adsorbent solid, first were prepared at known and constant concentrations. Then, the calculated amount of polymer was added to the silica dispersion. For the adsorption of p-DADMAC onto silica, the silica concentration was 4 g/L and the polymer concentration was varied from 0.1 to 0.6 g/L whereas, for the C-PAM adsorption, the silica concentration was 0.4 g/L and the polymer concentration was varied from 0.01 to 0.4 g/L. Then these mixtures were homogenized under slow agitation for 1 h to promote the adsorption of polymer onto the silica surface. Then the samples were centrifuged for 30 min at 10 000 rpm at 25°C. The equilibrium concentration of the polymer in the supernatant was measured by polyelectrolyte titration. The amount of adsorbed polymer, based on silica surface area, was determined from the concentration of excess polymer in the supernatant. The same procedure was used to determine the adsorption isotherms of PGA on cationized silica particles. The exact amount of cationic polymer added to saturate the silica surface without having free polymer in excess in solution was determined based on the cationic polymer adsorption isotherms on the surface of silica, according to the conditions of pH and of ionic strength. The cationic silica concentration was 1.35 g/L and the PGA concentration was varied from 0.03 to 0.3 g/L.
Electrophoretic Mobility and Zeta Potential The electrophoretic mobility of silica particles was measured initially, then 1 h after the addition of cationic polymer solution to the silica suspension, as described previously for adsorption isotherms, using a Zetasizer ZS from Malvern Instruments (Worcestershire, UK). The zeta potential (ζ) was calculated from the electrophoretic mobility (μe) using Henry's law:
3 ημ e ξ = --- ---------------------2 εε 0 f ( κ a )
(1)
where ε is the dielectric constant, ε0 the dielectric permittivity of vacuum, κ Debye’s length, and a the particle radius. For f(a), Oshima’s approximation was used: 1 2.5 ( 2 + 2exp ( – κ a ) ) – 3 f ( κ a ) = 1 + --- ⎛ 1 + -------------------------------------------------⎞ ⎝ ⎠ 2 κa (2) The value of f(a) is 1 when the electrolyte concentration is lower than 1 x 10-3 mol/L, and 1.5 for all other cases.
RESULTS AND DISCUSSION Pretreatment of Silica Particles with Cationic Polymers The adsorption of cationic polymer onto anionic silica particles is of the strong affinity type, as presented in Fig. 1. This behaviour is true for a polymer that is strongly charged, such as the p-DADMAC, or for a polymer with a lower charge density, such as the C-PAM. This adsorption is considered irreversible and very fast [13,14]. The adsorption of cationic polymer onto the surface of silica depends on the surface-charge density of the particle, on the charge density of the polyelectrolyte, and on the ionic strength of the solution [15]. Figures 2 and 3 present the amount adsorbed at saturation from adsorption isotherms of p-DADMAC and C-PAM on silica particles at various electrolyte concentrations. Whatever the cationic polyelectrolyte, the amount of polymer adsorbed rises with increasing pH of the solution, due to the increasing surface-charge density of the silica by the dissociation of the silanol groups. Under these conditions and because of the principle of electroneutrality, a more negative surface charge leads to more cationic polymer adsorption, because there is
+MAXMGG
+MAXMGG
P(
P(
;0OLYMER=EQG,
Fig. 1. Adsorption isotherm of p-DADMAC (u) and C-PAM (e) on the surface of silica at pH 6.5 and [NaCl] = 0.01 mol/L. 10
;.A#L=MOL,
Fig. 2. Amount of p-DADMAC adsorbed at silica surface saturation at various electrolyte concentrations.
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more charge of the silica particle to be neutralized [16]. In the case of C-PAM, which is pH dependent, as the pH decreases, the charge on the polyelectrolyte is reduced and more polymer molecules must be adsorbed to compensate for the surface-charge density of the silica [17]. The main difference between the pDADMAC and the C-PAM adsorption is their behaviours towards the salt concentration. The amount of p-DADMAC adsorbed at saturation (Fig. 2) increases with increasing ionic strength, while the amount adsorbed tends to decrease for the C-PAM at high ionic strength (Fig. 3). Indeed, we must distinguish here two regimes, which are the screening-enhanced adsorption (p-DADMAC) and the screening-reduced adsorption (C-PAM). Each regime, which appears as a specific combination of polymer and surface of opposite charge, depends on the balance of the electrostatic and nonelectrostatic forces between the polymer and the surface [18]. In the case of p-DADMAC, at low ionic strength the polymer molecules in the adsorbed layer are mainly in a flat configuration on the silica surface, since the mutual segmental repulsion between closed segments of similar charges prevents a strong coverage of the surface. Under these conditions, the polymer chains have no loops and tails, and the adsorbed quantity is low since the electrostatic contribution dominates. Indeed, it is well established that the adsorption of polyelectrolyte onto particles of opposite surface charge is charge-limited, since the accumulation of charge on the surface is still unfavourable. In fact, the electrostatic repulsions between the segments in the adsorbed layer limit the adsorption process. With increasing salt concentration, the segment repulsion and the electrostatic attraction between p-DADMAC and silica are screened by salt. The presence of salt promotes the charge accumulation because the range of electrostatic repulsion between the bound charges is reduced. At the same time, the
presence of salt can screen the intramolecular repulsion; the p-DADMAC rather behaves as an uncharged polymer, where it can have a conformation with loops and tails. Under these conditions, the amount of polymer adsorbed increases with increasing salt concentration [19]. At very high salt concentrations (0.1 mol/ L), the electrostatic contributions, i.e., the attractive interaction between the cationic pDADMAC and the negative silica and the segment–segment repulsion of p-DADMAC in the adsorbed layer, are screened totally by salt. The adsorption is theoretically expected to decrease under these conditions. However, results show higher adsorption of p-DADMAC onto the silica surface when ionic strength increases. This is due to the dominating effect of the non-electrostatic attraction between the p-DADMAC and the silica surface when the electrolyte concentration increases. Of course, a totally screened polymer can only adsorb onto a surface if there is non-electrostatic attractive interactions between the segments of the polymer and the surface [20]. This is exactly the case observed here between the silica surface and the p-DADMAC and, more specifically, with the quaternary amine group of the p-DADMAC [14,21,22].
In the case of C-PAM, at low ionic strength the amount of polymer adsorbed is very important because, with its low charge density, the segment–segment repulsions are less important, and C-PAM rather behaves as a neutral polymer and adsorbs on opposite surface charges with loops and tails. At the same time, when the segment charge of the polymer is lowered, more polymer molecules must be adsorbed to compensate for the surfacecharge density of the silica [14]. Between 0.001 and 0.01 mol/L, the electrolyte ions (Na+) start to compete with charged segments of the polymer for the compensation of the silica surface charges, leading to a slight increase of the adsorbed layer [23] because of conformational changes of
P(
adsorbed polyelectrolyte molecules [24]. At salt concentrations higher than 0.01 mol/L, a decrease in the polymer adsorption is observed, since the electrolyte ions start to compete successfully with the charged polymer segments, and are more effective in compensating the surface charge of the silica [18,25]. In fact, experiments have shown that the amount adsorbed remains relatively constant at lower electrolyte concentrations, but decreases at higher salt concentrations. Such behaviour is typical of the case where the electrostatic forces are responsible for the adsorption [26]. This does not exclude the simultaneous effect of non-electrostatic forces that can operate, even if they do not dominate, as in the case of the adsorption of C-PAM onto the silica surface [24,27]. Figure 4 presents the effect of salt concentration and pH on the zeta potential of pretreated silica particles at saturation. Results show that adsorption of both polymers onto the silica yields positive zeta-potential values. This is a good indication of the cationization of the silica surface through overcompensation. The zeta potential at saturation depends on the nature of the cationic polymer, that is to say the amount adsorbed and its charge density, and varies according to the ionic strength and pH of the solution. For both polymers, at similar ionic strength the zeta potential of cationic silica is slightly higher at pH 6.5 than at pH 4.5, since the amount of adsorbed polymer is more important at more alkaline pH. This leads to an increase in the number of cationic charges on the silica surface. However, in the case of C-PAM, the difference in zeta potential is not significant, since the difference in the amount of CPAM adsorbed according to the pH is low (Fig. 4). In the same way, as shown in Fig. 4, the zeta potential at saturation increases with the ionic strength from a low (0.001 mol/L) to a moderate level (0.01 mol/L), due to the higher amount adsorbed [28]. However, at very high ionic strength (0.1 mol/L), the zeta potential at
:ETAPOTENTIALM6
P(
+MAXMGG
;.A#L=MOL,
# 0!-P( # 0!-P(
Fig. 3. Amount of C-PAM adsorbed at silica surface saturation at various electrolyte concentrations.
P $!$-!#P(
P $!$-!#P(
;.A#L=MOL,
Fig. 4. Zeta potential at saturation of the cationic silica at various electrolyte concentrations.
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saturation decreases because of the screening of the charge of the adsorbed polymer by the electrolyte counter-ions [29]. The decrease in the zeta potential at saturation for the C-PAM at high ionic strength is also attributed to a lower adsorption at saturation. The zeta potential of silica pretreated with p-DADMAC is much higher than that of silica pretreated with CPAM, even though the amount adsorbed is less significant. This reveals that, to obtain a higher cationic zeta potential, the charge density of the adsorbed cationic polymer is much more important than the amount of adsorbed polymer at saturation.
+MAXMGG
ed silica. Figure 6 presents the adsorption capacity of pretreated silica under various conditions. Figure 6 shows that, whatever the pH and the polymer used, the adsorption increases to a maximum for a salt concentration of 0.01 mol/L, and then decreases at higher electrolyte concentrations. Results show that the adsorption of PGA onto cationized silica surfaces is greater at pH 6.5 than at pH 4.5 for each polymer at a given ionic strength. Finally, the adsorption of PGA is higher for silica particles pretreated with p-DADMAC, compared to trials with C-PAM at similar pH and ionic strength. In fact, if we compare the adsorption of PGA onto the surface of cationic silica acAdsorption of PGA onto Pretreated cording to the ionic strength (Fig. 6) with the zeta potential of cationic silica (Fig. 4), it is Silica Particles clear that they vary according to the same proThe adsorption of PGA onto silica partifile. cles pretreated with a cationic polymer is of the Figure 7 shows the effect of zeta potenstrong affinity type, as presented in Fig. 5. This tial on PGA adsorption levels. The higher the is true for p-DADMAC as well as for C-PAM, zeta potential, the higher the amount adsorbed whatever the electrolyte concentration was. onto the cationic silica particle for all experiOf course, PGA is not adsorbed onto the mental conditions studied (pH, ionic strength) unmodified silica surface due to electrostatic as well as the polymer used (similar experirepulsion of similar charges. On the other hand, mental conditions). Therefore, cationic charges it is clear that the PGA is adsorbed on pretreatmust be present on the surface of silica particles to promote PGA adsorption through a complexation mecha nism of the negative charge of the PGA with the positive charge of the cationic polymer [30,31]. Thus, we can consider that PGA adsorption is influenced strongly by electrostatic attraction [32,33] and is de;0'!=EQG, pendent on the zeta potential of cationized silica particles. Fig. 5. Adsorption isotherm of PGA onto silica surface covered by However, it is p-DADMAC (u) and by C-PAM (e) at pH 6.5 and [NaCl] = 0.01 mol/L. clear that the pH of
the solution and the nature of the cationic polyelectrolyte have a significant effect on the PGA adsorption, as shown by the linear relation between the zeta potential and the amount of PGA adsorbed. For example, the zeta potential of cationic silica is not affected very much by the pH (Fig. 4), whereas the amount of PGA adsorbed is influenced greatly by the pH (Fig. 6). In fact, the multilayer formation is influenced strongly by the electrostatic attraction, due to the presence of the loops of cationic polyelectrolyte dangling into the solution and creating a positive layer, which allows the complexation of the anionic charges of the PGA with the cationic charge of the p-DADMAC or the C-PAM. However, the complexation of polyelectrolyte of opposite charge is dependent greatly on the interlayer interpenetration. Indeed, the complexation is driven by the charge accessibility of the segments of adsorbing chains, which entangle into the precoated layer. This interlayer interpenetration could be influenced, for example, by the conformation of the adsorbing polyelectrolyte or by the flexibility of the underlying layer [32]. Under these conditions, the fixation of PGA onto the surface of cationic silica is enhanced at pH 6.5 because of the modification of the PGA conformation with the pH. Indeed, at pH 6.5, the charge density of PGA is higher than the charge density at pH 4.5, and the conformation of PGA is more extended at higher alkaline pH. It has been demonstrated that the degree of interdigitation is lower in the case of the adsorption of a coil-shaped structure than in the case of rod-like chains. This implies a reduced accessibility of the outer layer segments of both cationic polymers to the next adsorbing layer chains of PGA at pH 4.5. At the same time, it appears that the fixation of PGA onto a modified silica surface depends on the nature of the cationic polyelectrolyte preadsorbed onto silica, as presented in Fig. 8. Although the zeta potential of silica covered by C-PAM is low compared with the zeta
P $!$-!#P(
# 0!-P(
# 0!-
P $!$-!#P(
+MAXMGG
+MAXMGG
P $!$-!#
# 0!-P(
P(
P(
;.A#L=MOL,
:ETAPOTENTIALM6
Fig. 6. Amount of PGA adsorbed onto saturated silica covered by cationic polymer at various electrolyte concentrations. 12
Fig. 7. Amount of PGA adsorbed onto cationic silica according to its zeta potential.
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Preadsorption of Cationic Polymer and Adsorption of Complexes
+MAX0'!ADSORBEDMGG
Figure 9 compares two strategies for PGA removal by silica particles at pH 6.5. The goal of this trial was to determine the effectiveness of the silica pretreatment by
comparing these results to those obtained by the technique generally used in the industry, which consists of neutralizing anionic trash in the form of polymeric complexes, which are then fixed to fibres or particles. Thus, in the first case, which corresponds to the results presented previously by the adsorption isotherms, the PGA was eliminated by cationic silica completely covered by p-DADMAC. In the second case, the same amounts of products were used, but the PGA was first mixed with the p-DADMAC to form a polymeric complex, which was then added to the same quantity of silica used previously. By changing the order of addition, the second experiment allows us to determine the amount of PGA that can be removed from water by charge neutralization in solution. The results show clearly that preadsorption of a cationic polymer onto silica surfaces at pH 6.5, whatever the ionic strength, improves the removal of PGA compared to the case with the formation of a complex. According to the quantities added, the PGA is in excess in our experiments with regard to the p-DADMAC, and the resulting complex is negative. In this case, the structural parameter of the complexforming process is determined by the minor component that is bound completely by the oppositely charged polyelectrolyte, forming a neutralized core and a stabilizing shell of the excess component [36]. According to the charge density and weight ratio of both polymers, the complex charge ratio (n+/n-) varies from 0.24 to 0.53. As long as negatively charged complexes were added to negative silica particles, adsorption was not possible. To fix the PGA in the form of a polymeric complex onto the surface of silica, the polymeric complex must be positive [37]. To have a neutral complex, corresponding to a charge ratio of 1.1 [38], it would be necessary in this experiment to add 1.5–4 times more p-DADMAC. For equivalent quantities of chemical additives, the pretreatment of the silica surface improves PGA removal from the water phase compared to the formation of polymeric complexes in so-
!MOUNTOFCATIONICPOLYMERADSORBEDMGG
Fig. 8. Amount of PGA adsorbed onto cationic silica covered by pDADMAC (u) and C-PAM (e) according to the amount of cationic polyelectrolyte adsorbed onto silica at pH 6.5.
!MOUNTOF0'!ELIMINATEDMGG
potential of silica covered by p-DADMAC, the difference in the amount of PGA adsorbed is not as important, according to the nature of the cationic polyelectrolyte. Furthermore, it is clear that, in the case of C-PAM, the amount of cationic polymer adsorbed onto the surface of silica has a slight influence on the fixation of PGA. Indeed, the amount of PGA adsorbed increases with the amount of C-PAM preadsorbed onto the silica particles, as shown in Fig. 8. This can be explained by the fact that the accessibility of the anionic charge of the PGA to the cationic charge of the C-PAM is greater than in the case of p-DADMAC. Indeed, it has been demonstrated that the total amount of polymer adsorbed depends on the thickness of the previously adsorbed layer, with a higher adsorbed amount typically being found with thicker layers [34]. It is generally the case for weak polyelectrolytes such as C-PAM, where the conformational restrictions due to entanglement are less important. Moreover, by comparing the hydrodynamic thickness of the layers of cationic polyelectrolyte adsorbed, it is clear that the interlayer interpenetration is favoured in the case of CPAM. Indeed, in the range of ionic strengths studied, where the hydrodynamic layer thickness increases with increasing ionic strength [29,35], it varies from 1 to 7 nm for ionic strengths ranging from 0.001 mol/L to 0.1 mol/L for p-DADMAC [28], whereas it varies from 15 to 50 nm for an ionic strength ranging from 0.001 to 0.1 mol/L in the case of C-PAM [25,24]. Therefore, it is clear that the charge accessibility is favoured in the case of C-PAM.
lution, which are then fixed onto particles. Furthermore, the pretreatment requires less cationic polymer to eliminate an equivalent quantity of PGA compared to the quantity used for the charge neutralization in solution.
CONCLUSIONS The purpose of this study was to understand how commercial cationic polymers can affect the deposition of a detrimental model substance onto silica nanoparticles. The polymers generally used in the paper industry lead to the flocculation of DCS that interact in a way different from silica, according to the salt concentration of the solution. The adsorption of pDADMAC increases with increasing ionic strength (screening-enhanced adsorption), whereas the adsorption of C-PAM decreases with increasing salt concentration (screeningreduced adsorption). The amount of adsorbed cationic polymer depends as well on the pH of the solution and on the polymer-charge density. The interaction between silica pretreated by cationic polymers and PGA is driven by electrostatic attraction, but above all depends on the interlayer interpenetration. The amount of PGA adsorbed onto the cationic silica surface depends on the zeta potential of the cationic silica, but also on the charge accessibility of the outer layer segments. Finally, the pretreatment of silica particles by cationic polyelectrolyte improves the removal of a model substance for anionic trash compared with the charge neutralization in solution and the formation of polymeric complexes. In view of the results presented, this technique, i.e., the charge complexation of anionic trash by cationicmodified silica particles, makes it possible to decrease the amount of chemical additives required to minimize the detrimental effect of DCS in white water.
ACKNOWLEDGEMENT The authors gratefully acknowledge the
!DSORPTONBYCATIONICSILICA #OMPLEXESADSORPTION
;.A#L=MOL,
Fig. 9. PGA removal with or without the preadsorption of cationic polymer on the surface of silica.
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Canada Research Chair in Value-added Paper for their financial support.
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REFERENCE: GUYARD, A., CHABOT, B. and DANEAULT, C., Use of Cationic Polyelectrolytes for the Fixation of Anionic Trash onto Silica Particles, Journal of Pulp and Paper Science, 33(1):9– 14 January/February/March 2007. Paper presented at the 92nd Annual Meeting of the Pulp and Paper Technical Association of Canada, February 6-10, 2006. Not to be reproduced without permission from the Pulp and Paper Technical Association of Canada. Manuscript received November 14, 2005; revised manuscript approved for publication by the Review Panel November 8, 2006. KEYWORDS: CATIONIC COMPOUNDS, POLYELECTROLYTES, RETENTION AIDS, ANIONIC COMPOUNDS, STICKIES, FIXING, SILICA, ADSORPTION.
JOURNAL OF PULP AND PAPER SCIENCE: VOL. 33 NO. 1 JANUARY/FEBRUARY/MARCH 2007
