A Useful Equation for Estimating Surface Charge of Pulp Fibers (original) (raw)
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Tappi Journal, 2005
The externally exposed charge of pulp fibers plays a significant role in the interfiber bond formation. It is also beneficial for the necessary good adsorption of the additives used for paper manufacturing. The quantification of the polyelectrolyte adsorption capacity of the fibers is a common method used to measure surface charge. A linear cationic polyelectrolyte with high charge density, the p-DMDAAC (poly-DiMethylDiAllylAmmonium Chloride) with a molecular mass higher than 100,000 Daltons, is used under the assumption that it does not penetrate the micropores of the cell wall. In order to build the adsorption isotherm, pulp samples are added to solutions of different concentration of p-DMDAAC and after equilibrium is reached, the concentration of polymer in the solution is determined by polyelectrolyte titration. We propose a simple equation that can be very useful to measure the surface charge since it allows analyzing the isotherms with a uniform criterion.
Interactions Between Cationic Polyelectrolyte and Pulp Fines
Bioresources, 2011
Papermaking pulps are a mixture of fibres, fibre fragments, and small cells (parenchyma or ray cells), usually called pulp fines. The interactions between pulp fines and a cationic copolymer of acrylamide and acryloxyethyltrimethyl ammonium chloride were investigated based on solid-liquid isotherms prepared under different turbulence, and subsequent advanced surface characterization using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The surface charge and surface area of pulp fine substrates were measured by methylene blue sorption-XPS analysis and nitrogen adsorption combined with mercury porosimetry, respectively. The driving force behind polyelectrolyte adsorption was the amount of the surface anionic charge, whereas surface area appeared to be of less importance. Based on a comparison of solid-liquid and XPS sorption isotherms, different polyelectrolyte conformations were suggested, depending on the types of fines: A flatter conformation and partial cell-wall penetration of polyelectrolytes on kraft fines from freshly prepared pulp, and a more free conformation with extended loops and tails on lignocellulosic fines from recycled pulp. Additionally, ToF-SIMS imaging proved that recycled pulp fines contained residual de-inking chemicals (primarily palmitic acid salts) that possibly hinder the electrostatic interactions with polyelectrolytes.
BioResources, 2013
The charge density of a bleached Kraft hardwood pulp, subjected to layer-by-layer adsorption of the oppositely charged cellulose derivative polyelectrolytes hydroxyethylcellulose ethoxylate, quaternised (HECE), and carboxymethyl cellulose (CMC), was studied by polyelectrolyte titration as a function of pH and ionic strength. The experimental design included a simultaneous variation of the experimental parameters, and the trends were evaluated with the help of partial least squares regression. As expected from the literature, the data indicate that both pH and ionic strength influence the charge of cationic fibers. It is also obvious that CMC as an outermost layer is more sensitive to changes in pH than the deprotonation of ≡COOH groups suggests. High ionic strength seems to be beneficial for the adsorption of HECE, while the pH dependence seems much more complicated. The non-linear pH dependence indicates that, in addition to electrostatic interactions, entropy factors and hydrogen bonding between OH groups on both the substrates and ligands are responsible for the adsorption, which is in agreement with literature on the subject.
Role of surface charge in deposition of filler particles onto pulp fibres
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1998
The effect of cationic polyethylenimine (PEI ) on colloidal stability of ground calcium carbonate and its deposition on pulp fibres suspended in water was investigated. The adsorption of PEI on negatively charged CaCO 3 particles causes destabilization due to the elimination of charge. With increasing additions of PEI, restabilization of positively charged CaCO 3 takes place. Based upon these results the filler was pretreated with PEI in order to encourage its deposition on negatively charged fibres. Two levels of PEI addition were used to produce either CaCO 3 aggregates or dispersed particles. The extent of deposition, the deposition time t, and the capture efficiency a0 were established. The results indicate that positively charged filler aggregates deposit faster than dispersed particles.
Acid/base and metal adsorption properties of CMC-type softwood Kraft pulps of different charge
Nordic Pulp & Paper Research Journal, 2006
The aim of this work was to characterize a series of carboxymethylated pulps of various degrees of substitution (40-280 µmol/g) with respect to their acid/base and metal adsorption qualities. The study was performed using potentiometric titrations, batch experiments and AAS/AES analyses. With respect to the acid/base properties of the different pulps, the study has shown that the Basic Stern Model and the Constant Capacitance Model both can be used to describe the different pulps in the region of interest. For the most highly substituted pulp, however, the CCM should preferably be used to describe the acid/base properties at low pH. The metal ion adsorption study comprised a simultaneous presence of four metal ion, namely Na + , K + , Ca 2+ and Mg 2+. With respect to these interactions data showed that the Donnan ion exchange model could well explain the simultaneous adsorption of all four metal ions, independently of the degree of "CMC substitution". The fit of the Donnan model to the data was approximately equal independently on whether the Constant Capacitance Model or the Basic Stern Model was used to model the pH-dependent fibre charge. The conclusion to be drawn from this study is that the Donnan model can be applied within a wide range of pulp charge, as long as there are only mono-carboxylate groups on the fibre and these are characterised by a valid acid/base model.
Fiber charge characteristics of pulp suspension containing aluminum sulfate
Journal of Wood Science, 2002
Fiber charge characteristics of pulp suspensions containing aluminum sulfate were investigated with relation to adsorption behavior of aluminum components on the pulp fibers by streaming potential measurement using a particle charge detector, X-ray photoelectron spectroscopy, and X-ray fluorescence analysis. When aluminum sulfate was added to a pulp suspension prepared using deionized water, a streaming potential of the suspension went from negative to slightly negative according to the adsorption of aluminum components on the pulp fibers. Subsequent addition of a dilute NaOH solution to the suspension drastically cationized the fibers in the pH range of around 5 by predominant and homogeneous adsorption of cationic aluminum complexes on the fiber surfaces. However, the aluminum flocs that formed heterogeneously on the fiber surfaces at higher pH by further alkali addition made nearly no contribution to cationization of the fibers, although the abundant aluminum components were retained in the pulp sheets. Therefore, only aluminum cations adsorbed uniformly on the fiber surfaces perform well to control the charge properties of the pulp fibers at the wet end; and the preferential aluminum adsorption behavior on the fiber surfaces, by utilizing the required amounts of hydroxyl ions, probably accounts for the effective cationization of the fibers under acidic to neutral papermaking conditions.
Adsorption kinetics of cationic surfactant onto pulp fibres
Adsorption of cationic compounds on cellulosic fibres totally changed their surface chemistry. The paper is focused on the modification of pulp fibres by a cationic surfactant (quaternary ammonium salts). The work deals with surfactant adsorption kinetics and modes of surfactant adsorption on the cellulosic fibre surface. It was found that the adsorption curve had a rising character. The results showed that the surfactant was not adsorbed onto the fibre surface in monolayer. It can be assumed that the surfactant was also adsorbed into the internal porous structure of the fibres. To monitor the surfactant adsorption on fibres, the method of streaming potential with polyelectrolyte titration was used.
Determination of fiber charge components of Lo-Solids unbleached kraft pulps
Journal of Colloid and Interface Science, 2004
Four different titration methods for measurement of fiber charge were used in this study. Each method gave different fiber charge values depending on the acidity of the end point and the interaction between the fiber chemical components and the titrant. Also, the interactions between the ionizable groups on the fiber had significant effects on the interpretation of these results. The conductometric titrations showed trends similar to the results obtained from the potentiometric titration. The conductometric titrations with NaOH produced higher fiber charge values, higher than the titrations with NaHCO 3 . The differences between the results obtained from the potentiometric and polyelectrolyte titrations, which were associated with the dissolved fiber components during the delignification, were linearly related to the Kappa number of pulps. The positive intercept of this linear relationship indicated that the kraft pulping process not only removed the ionizable groups associated with the dissolved components, but at the same time provided conditions to form new ionizable groups in the fibers. The polyelectrolyte titration results indicated that the lignin content in the fibers did not affect the fiber surface charge. Data extracted from the FTIR spectra of protonated fibers were highly correlated with the fiber charge values obtained from the conductometric titration with NaOH. 2004 Elsevier Inc. All rights reserved.
Fractionating polydisperse polyelectrolytes in packed beds of cellulose fibers
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2011
Low molecular weight fractions of polydisperse polyelectrolytes can penetrate the porous structure of cellulose fibers, whereas the high molecular weight fraction cannot. The effects of polydispersity on polyelectrolyte adsorption, especially for polyelectrolytes with a very broad size distribution, often encountered in industry, can be very pronounced. Previously we showed that the adsorption rate constant for polyethylene imine (PEI) adsorbing on pulp fibers, as well as the maximum adsorption capacity, roughly increased by a factor of 4, when the pH was increased from 6 to 10. The increase in adsorption capacity was explained by the decrease in the size of a PEI molecule, by almost a factor of two. The increase in rate was explained by the increase in the low molecular weight fraction of PEI which could penetrate the fibers. To explain the results, this low molecular weight fraction should be four times as large at pH 10, compared to pH 6. Here, we discuss the results of experiments on PEI adsorption in packed beds of cellulose fibers, which confirm this hypothesis.
Journal of Dispersion Science and Technology, 2009
The adsorption of cationic polyelectrolytes (C-PAMs and PDACMAC) with different charge densities and molecular weights on silica and cellulose model surfaces was examined using a quartz crystal microbalance with dissipation, QCM-D. The conformation and viscoelastic properties of the adsorbed polyelectrolyte layers were studied by modelling the data with the Q-Tools program. When comparing the adsorption behavior on cellulose and silica a clear difference both in adsorption kinetics of polyelectrolytes and the viscoelastic properties of the formed polyelectrolyte film was observed. On cellulose the polyelectrolyte films were viscous and more dissipative at the beginning of the adsorption but when the adsorption proceeded the layers became more rigid and stiffer, in contrast to the behavior on silica.