Colloid Titration Research Articles

A water-soluble cationic flocculant synthesized by dispersion polymerization in aqueous salts solution

A water-soluble cationic flocculant, the copolymer of acrylamide (AM) and acryloylamino-2-hydroxypropyl trimethyl ammonium chloride (AMHP), has been synthesized through dispersion polymerization in aqueous ammonium sulfate ((NH 4) 2SO 4) solution. The polymerization was initiated by potassium persulfate (KPS) using poly(2-methylacryloylxyethyl trimethyl ammonium chloride) (PDMC) as the stabilizer. The copolymer obtained was characterized using Fourier-transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, colloidal titration and optical microscopy. Its flocculation properties were evaluated with 0.25 wt% kaolin suspensions using a standard jar test. The zeta potential of the supernates at different flocculant dosages was measured simultaneously. The results demonstrate the superiority of the copolymer over the commercial polyacrylamide as a flocculant.

Determination of zeta potential and cationic demand in ECF and TCF bleached pulp from eucalyptus and flax. Influence of measuring conditions

The electrical nature of cellulose fibres is known to govern flocculation, retention and drainage mechanisms during the papermaking process. Zeta (ζ) potential provides useful information towards better control of wet-end chemistry in respects such as the dosaging of chemical aids. The purpose of this work was to study two electrokinetic properties (ζ potential and cationic demand) in ECF (elementary chlorine free) and TCF (totally chlorine free) bleached pulps from eucalyptus and flax, and examine the influence of pH and conductivity on measurements of such properties made with various methods based on the streaming potential, electrophoresis, polyelectrolyte titration and colloidal titration. Measurements of the electrokinetic properties made at high conductivities (C > 0.1 mS/cm) afforded no discrimination between pulp types in terms of electric charge. In fact, the conductivity used had a strong influence on measurements and shifted ζ potential to less negative values at high levels and to more negative values at low levels. The streaming potential technique proved to be more sensitive to changes in the properties (pH and conductivity) of the fibre suspension than did electrophoresis. Conductivity also influenced polyelectrolyte adsorption in the determination of cationic demand. The study also involved assessing the effect of low conductivities (0.01 < C < 0.1 mS/cm), which allowed fibre types and bleaching processes to be easily distinguished. Based on the results, accurately characterizing and identifying not only pulp types, but also the effects of mechanical, chemical and biochemical treatments on fibres, requires measuring the electrokinetic properties at a fixed pH and low conductivity.

Gamma radiation-induced dispersion polymerization in aqueous salts solution for manufacturing a cationic flocculant

Abstract A water-soluble cationic flocculant, a copolymer of acrylamide (AM) and acryloylamino-2-hydroxypropyl trimethyl ammonium chloride (AMHP), was synthesized through dispersion polymerization method in aqueous ammonium sulfate ((NH 4 ) 2 SO 4 ) solution. The polymerization was initiated by gamma-radiation using poly(2-methylacryloylxyethyl trimethyl ammonium chloride) (PDMC) as the stabilizer. The obtained copolymer was characterized by using Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), colloidal titration and optical microscopy. Its flocculation properties were evaluated with 0.25 wt% kaolin suspensions using a standard jar test. The zeta potential of supernatant at different flocculant dosage was simultaneously measured. The results demonstrate the superiority of the copolymer over the commercial polyacrylamide as a flocculant.

Charge characteristics of humic and fulvic acids: Comparative analysis by colloid titration and potentiometric titration with continuous p K-distribution function model

Charge characteristics of humic and fulvic acids of a different origin (inshore soils, peat, marine sediments, and soil (lysimetric) waters) were evaluated by means of two alternative methods – colloid titration and potentiometric titration. In order to elucidate possible limitations of the colloid titration as an express method of analysis of low content of humic substances we monitored changes in acid–base properties and charge densities of humic substances with soil depth, fractionation, and origin. We have shown that both factors - strength of acidic groups and molecular weight distribution in humic and fulvic acids – can affect the reliability of colloid titration. Due to deviations from 1:1 stoichiometry in interactions of humic substances with polymeric cationic titrant, the colloid titration can underestimate total acidity (charge density) of humic substances with domination of weak acidic functional groups (p K > 6) and high content of the fractions with molecular weight below 1 kDa.

Adsorption characteristics of cationic-modified poly (vinyl alcohol) on cellulose fibers–A qualitative analysis

Poly (vinyl alcohol) (PVA) has been widely used in papermaking and coating processes. However, its application as a strength agent is confined due to its poor affinity to adsorb on fibers. To address this problem, PVA with different molecular weights were rendered cationic via introducing quaternary ammonium groups along PVA chains. The work presented in this paper focused on the adsorption behavior of the cationic-modified PVA (C-PVA) on cellulose fibers (sulfite pulps). The results, obtained from polyelectrolyte titration, indicated that the adsorption of C-PVA with low charge densities was enhanced, regardless of polymer molecular weight (MW). However, the C-PVA with high MW had markedly lower maximum coverage than the C-PVA with low MW. Adsorption of low MW polymers achieved saturation at a relatively shorter period than high MW polymers. The influence of pH, ionic strength (or electrolyte concentration) and temperature on the adsorption of C-PVA on fibers were also investigated. Apart from the study on the adsorption using colloidal titration, the degree of substitution of cationic groups on PVA was quantified using 1H NMR.

Quantification of hydrolytic charge loss of DMAEA-Q-based polyelectrolytes by proton NMR spectroscopy and implications for colloid titration

Copolymers of acrylamide and quaternised dimethylaminoethyl acrylate (DMAEA-Q) constitute an economically important range of cationic polyelectrolytes used in sludge conditioning. The latter treatment involves charge neutralisation and bridging induced by these polymers. Since both of these phenomena rely on charge-driven sorption onto the negatively charged colloidal particles, the accurate assessment of their charge density is of primary importance in polyelectrolyte characterisation. The experimental determination of this characteristic generally relies on colloidal charge titration, in which the cationic polymer is titrated against an anionic polymer. Hereby, one of the requirements to have a stoichiometric reaction between the oppositely charged polymers is a sufficiently low polymer concentration. In this study, it is shown that such a low polymer concentration may entail a pronounced hydrolysis effect for DMAEA-Q-based polymers, which leads to a release of the cationic side groups and hence causes considerable errors on the charge titration results. Proton nuclear magnetic resonance spectroscopy was applied to investigate the fast hydrolysis kinetics of DMAEA-Q polymers together with time-dependent charge titration measurements. Diffusion NMR spectroscopy was used to assist in establishing the nature of the hydrolysis compounds. The results from both techniques indicate that a high degree of hydrolysis is reached within minutes after dilution of a concentrated polymer stock solution into aqueous solutions of slightly acidic to neutral pH values. Therefore, a modification to the classic colloid titration procedure is proposed, using a buffered dilution liquid to avoid polymer hydrolysis. It is shown that a buffer pH value of 4.5 avoids not only polymer hydrolysis effects but also possible protonation of the anionic titrant, thereby avoiding overestimation of the charge density. By means of this procedure, reproducible and time-independent charge titration results are obtained.

Polyelectrolyte complex characterization with isothermal titration calorimetry and colloid titration

Abstract Isothermal titration calorimetry (ITC) and colloid titration (CT) were used to characterize aqueous polyelectrolyte complex formation between strong polyelectrolytes, poly(diallyldimethylammonium chloride) and potassium poly(vinyl sulfate) and between weak polyelectrolytes, polyvinylamine (PVAm) and carboxymethyl cellulose (CMC). ITC gives information about the evolution of polyelectrolyte complex properties but does not give good measure of the charge balance composition. By contrast, CT determines the charge balance endpoint but reveals nothing about the path to the endpoint. For strong polyelectrolyte complexes based on fixed charge polymers, the CT curves are very clean giving a sharp endpoint. The corresponding ITC curves are relatively simple although the endpoints are not as distinct as CT. ITC does, however, indicate the onset of phase separation. For weak polyelectrolyte complexes (PVAm/CMC) based on polymers with labile charges, ITC gives complicated curves which are sensitive to pH, ionic strength and the order of addition. The most dramatic effects occur at pH 5–5.9 where we propose that complex formation induces the CMC to ionize further during the titration.

Simultaneous Depolymerization and Decolorization of Chitosan by Ozone Treatment

Currently, depolymerization and decolorization of chitosan are achieved by chemical or enzymatic methods, which are time consuming and expensive. Ozone has been shown to be able to degrade macromolecules and remove pigments due to its high oxidation potential. In this study, the effects of ozone treatment on depolymerization and decolorization of chitosan were investigated. Crawfish chitosan was ozonated in water and acetic acid solution for 0, 5, 10, 15, and 20 min at room temperature with 12 wt% gas. In this study, the effects of ozone treatment on depolymerization and decolorization of chitosan were investigated by measuring the molecular weight, viscosity, and color of chitosan. The color of ozone-treated chitosan was analyzed using a Minolta spectrophotometer. The degree of deacetylation was determined by a colloid titration method. Molecular weight of ozone-treated chitosan in acetic acid solution decreased appreciably as the ozone treatment duration increased. Ozonation for 20 min reduced the molecular weight of the chitosan by 92% (104 kDa) compared to the untreated chitosan (1333 kDa) with a decrease in viscosity of the chitosan solution. Ozonation for 5 min markedly increased the whiteness of chitosan with a molecular weight of 432 kDa; however, further ozonation resulted in development of yellowness. In the case of the ozonation in water, there were no significant differences in the molecular weight and color between ozone-treated chitosans. This study showed that ozone can be used to modify molecular weight and remove pigments of chitosan without chemical use in a shorter time and with less cost.

Preparation of PVA-GA-CS/PVA-Fe-SA bipolar membrane and its application in electro-generation of 2,2-dimethyl-3-hydroxypropionic acid

PVA-GA-CS/PVA-Fe-SA bipolar membrane was prepared by a paste method. PVA-sodium alginate (SA) and PVA-chitosan (CS) were cross-linked by FeCl 3 and glutaraldehyde (GA), respectively. The charge densities of PVA-CS and PVA-SA solutions were determined by the colloid titration. The swelling level of bipolar membrane was in the range of 25–85%, meanwhile the permeability and the ion-exchange capacity as well as co-ion transport properties was investigated. FTIR was applied to analyze the functional groups of the bipolar membrane. Furthermore, SEM photographs of the BPM cross-section illustrated a structure that consists of an anion layer (PVA-GA-CS) and a cation layer (PVA-Fe-SA). TG analysis of PVA-GA-CS/PVA-Fe-SA bipolar membranes exhibited a good thermal stability. PVA-GA-CS/PVA-Fe-SA bipolar membranes were used as the separator in the electrolysis cell for electro-generation of 2,2-dimethyl-3-hydroxypropionic acid. The average current efficiency was 52.2%, and the highest current efficiency reached 68.9%.

Key considerations in the determination of polyelectrolyte concentration by the colloidal titration method

Key considerations in the determination of polyelectrolyte concentration by the colloidal titration method

Key considerations in the determination of polyelectrolyte concentration by the colloidal titration method

Medium or high charge density cationic polyelectrolytes are frequently used for water treatment. In the papermaking wet-end they are used as retention agents or as flocculating aids. Negative polyelectrolytes that enter the papermaking system increase the demand for cationic polyelectrolytes. Polyelectrolyte concentration can be determined by the colloidal titration method, using either of two options for detecting the endpoint: i) visual observation or spectrophotometric determination of the colour change of an indicator, or ii) streaming current measurement. This work discusses the best conditions for the application of the titration using spectrophotometric measurement for the end point detection. Poly-diallyldimethylammonium chloride was used as the cationic polyelectrolyte, potassium polyvinyl sulphate as the negative polyelectrolyte, and o-toluidine blue as the positive indicator dye. The polyelectrolyte concentration range, interference from the metal ions affecting the indicator color change, the optimal indicator concentration to avoid precipitation problems, and the effect of adding a surfactant to the indicator solution were also considered. Titration curves were analyzed and optimized. Under these conditions the technique provided results with acceptable precision.

Flocculation properties and adsorption kinetics of cationic starches in kaolin suspensions

AbstractThe flocculation characteristics of cationic starches with degree of substitution (DS 0.32–0.63) have been evaluated in 1.0 wt % kaolin suspension by spectrophotometry and colloid titration. Cationic starch is found to be an effective flocculant for removal of anionic suspension particles. Changes in the electrokinetics of kaolin as a function of pH were investigated in the absence of flocculant. The results show that kaolin in water exhibits a negative surface charge at pH &gt; 2.5. The negative hydrophilic surface sites of kaolin are responsible for the adsorption of cationic starch molecules. The experimental data of the adsorption of cationic starch (DS 0.51) follow a Langmuir isotherm with maximum adsorption capacities of 16.89 mg/g. For the adsorption of cationic starch, chemical reaction seems significant in the rate‐controlling step and the pseudosecond‐order chemical reaction kinetics provides the best correlation for the experimental data. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Preparation and characterization of N-(2-carboxybenzyl)chitosan as a potential pH-sensitive hydrogel for drug delivery

A novel water-soluble chitosan derivative [ N-(2-carboxybenzyl)chitosan, CBCS] was synthesized. The chemical structure of CBCS was characterized by FTIR, 1H NMR and UV spectroscopies. The degree of substitution (DS) of N-2-carboxybenzyl was determined by colloid titration. In different pH buffer solutions, the swelling characteristics of hydrogels based on CBCS (CBCSG) prepared by crosslinking with glutaraldehyde have been studied. Results showed that the swelling ratio (SR) of CBCSG decreased with an increase of the amount of glutaraldehyde, and that CBCSG swelled more significantly in alkaline solution than in acidic medium, showing the lowest SR at pH 5.0. The SR of CBCSG increased with the raising of the DS of the N-2-carboxybenzyl group in alkaline solution, but no significant change was observed in an acidic environment. CBCSG showed swelling reversibility when alternately soaked in pH 1.0 and 7.4 buffer solutions. Release profiles of fluorouracil (5-FU), a poorly water-soluble drug, from CBCSG were studied under both simulated gastric and intestinal pH conditions. The release was much quicker in pH 7.4 buffer than in pH 1.0 solution. Results indicated that CBCS could be a potential pH-sensitive carrier for colon-specific drug delivery system.

Full exploitation of Cannabis sativa as reinforcement/filler of thermoplastic composite materials

Hemp strands and cane straw of hemp have been used as reinforcement and filler of polypropylene composites obtained by injection moulding. The aim of the work was to improve the tensile properties of hemp composites and make them more similar to those obtained with glass fibre composites. For this reason, maleated polypropylene (MAPP) was used as compatibility agent in hemp strand and hemp straw composites. MAPP decreases the hydrophobic nature of PP matrix and enhances the dispersion and the adhesion at interface between both constituents. The hydrophilic property of material’s surface was determined by colloidal titration. The length and diameter of the fibre reinforcement during processing were analysed and their aspect ratio calculated. The tensile results obtained showed that the mechanical properties of hemp strand composites can amount to 80% of the mechanical properties of glass fibre composites.

Comparison of cationic demand between olive wood organosolv pulp and eucaliptus kraft pulp

The present work has evaluated the variation of cationic demand in function of refining degree for two unbleached cellulosic pulps: a eucalyptus pulp proceeding from a kraft process and an olive wood pulp proceeding from an organosolv process. In the organosolv process, a mixture of ethanolamine, sodium hydroxide and water has been used. For each kind of pulp, fines percentage, weighted medium length of fines, specific surface, carboxyl group's content, water retention value and cationic demand in function of refining degree have been obtained. Cationic demand has been evaluated by means of colloidal titration. Results obtained suggest the use of olive wood organosolv pulp for industrial purposes need to be enhanced. To achieve the same refining degree than eucalyptus pulp, a lot of refining time was needed. It has been observed also that in eucalyptus pulp, polymer fixation by ionic exchange is higher than adsorption. On the other hand in olive pulp, adsorption of cationic polymers prevailed over electrostatic interactions. The great content of fines in olive pulp and its higher values of carboxyl group's density could explain this behaviour.

Biodegradable Hyaluronic Acid/N‐Carboxyethyl Chitosan/Protein Ternary Complexes as Implantable Carriers for Controlled Protein Release

An ampholytic N-carboxyethyl chitosan (CEC), with various isoelectric points (IPs), was synthesized by grafting acrylic acid on chitosan utilizing Michael's reaction. Compared to native chitosan, CEC has enhanced water solubility and dramatically accelerated enzymatic degradation; the rate of degradation is proportional to the degree of substitution (DS). The results from turbidimetric titration and fluorescence studies revealed that CEC formed complexes with either hyaluronic acid (HA) or bovine serum albumin (BSA) within a certain pH range. The HA/CEC/BSA ternary complexes could be prepared by colloid titration with quantitative yield and BSA entrapment. The rate of BSA release from the complexes was affected by pH, ionic strength, DS of CEC, and the molecular weight (MW) of HA. The endurance of BSA release from the complexes could be extended up to 20 d by formulating them with high-MW HA and CEC with low DS.BSA release profiles from HA/CEC-2/BSA complexes.

Synthesis of water‐soluble cationic polymers with star‐like structure based on cyclodextrin core via ATRP

AbstractA range of novel cationic star‐like polymers (Star‐P(MeDMA)s) were synthesized through atom transfer radical polymerization (ATRP) by core‐first method, using a β‐cyclodextrin initiator with 21 initiation sites (21Br‐β‐CD). Methyl chloride‐quaternized 2‐(dimethylamino)ethyl methacrylate (MeDMA) was polymerized in an aqueous medium using 21Br‐β‐CD, Cu(I)Br, and 2,2′‐dipyridyl as an initiator, catalyst, and ligand, respectively. The effects of polymerization temperature and monomer/initiator ratios on the degree and kinetics of polymerization were investigated. The molecular weights, hydrodynamic sizes, and charge densities of the quaternized polymers were characterized using gel permeation chromatography (GPC), dynamic light scattering (DLS), and colloidal titration, respectively. The results demonstrated that the moderate aqueous solubility of the 21Br‐β‐CD initiator had significant impact on the physicochemical properties of the obtained star polymers. The polymerization of 500/1/2/5 ([M]0/[I]0/[Cu(I)0/[L]0]) at 90 °C for 6 h was found to be the best condition to synthesize the proposed cationic star polymer with well‐defined structures in aqueous medium. The nonlinear relationship between the apparent charge density and the particle size of the cationic star polymers was further revealed by GPC and DLS measurements. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6345–6354, 2005

Preparation of Monomodal Polyelectrolyte Complex Nanoparticles of PDADMAC/Poly(Maleic Acid-alt-α-methylstyrene) by Consecutive Centrifugation

We report on the refinement of anionic and cationic nanoparticles of nonstoichometric polyelectrolyte complexes (PEC) by consecutive centrifugation, which was studied by dynamic light scattering (DLS), atomic force microscopy (AFM), colloid titration and infrared spectroscopy (IR). PEC dispersions were prepared by mixing poly(diallyldimethylammonium chloride) (PDADMAC) and sodium poly(maleic acid-alt-alpha-methylstyrene) (PMA-MS) at the monomolar mixing ratio of n-/n+ = 1.50 (anionic PEC) and 0.66 (cationic PEC), respectively, and the polymer concentration of c(POL) = 0.002 M. The particle size (Rh), titrable charge amount, and IR spectra were determined for both dispersions in the original state, after the first centrifugation and after the second centrifugation. Freshly prepared PEC dispersions contained two different particle sizes: around 10-25 nm (small particles) and around 100 nm (large particles). Consecutive centrifugation of freshly prepared PEC dispersions resulted in the separation of highly charged excess polyelectrolyte (PEL) and small PEC particles from a low charged coacervate phase of the desired larger PEC particles. After the second centrifugation, the coacervate phase of both dispersions PEC-1.50 and PEC-0.66 consisted of monomodal particles sizing around 100 nm. These results were supported by AFM measurements on the respective dispersions deposited on glass plates. PEC-1.50 particles tended to adopt slightly smaller sizes ( approximately 90 nm) in comparison to PEC-0.66 ones (approximately 110 nm). No significant influence of the PDADMAC molecular weight on the particle size was found. IR spectroscopy showed changes in the environment of the carboxylate groups of PMA-MS by consecutive centrifugation. The centrifuged PEC-1.50 dispersions showed remarkable long-term stability over more than a year. The high macroscopic stability of the studied PEC dispersions is presumably due to repulsive electrostatic interparticle interactions and attractive hydrophobic intraparticle interaction. The introduced monomodal PEC particles might be projected as latex analogues or as nanocarriers for drugs and proteins.

지시약 적정법 및 분광광도법에 의한 양이온 고분자 전해질의 전해밀도 정량

Polyelectrolyte titration, which was called colloid titration is based on the stoichiometric reaction between oppositely charged polyelectrolytes, This can be used, for instance, to determine the charge density of a cationic polyelectrolyte, using an anionic polyelectrolyte of known charge density, such as potassium polyvinyl sulfate (PPVS). The technique requires a suitable method of end-point detection and there are several possibilities. In this work, two methods have been investigated: visual titrimetry based on the color change of a cationic dye (o-toluidine blue, o-Tb) and spectrophotometry based on the absorbance change corresponding to the color change of the same dye. These have been applied to several cationic polyelectrolytes with different charge density and molecular weight. In all cases, the cationic charge was due to quaternary nitrogen groups. In the case of cationic dye, it was shown that the sharpness depends on the charge density of cationic polyelectrolyte. With the polyelectrolytes of lower charge density, the binding to PPVS is weaker and binding of the dye to PPVS can occur before all of the polyelectrolyte charge has been neutralized. However, by carrying out titrations at several polyelectrolyte concentrations, good linear relationships were found, from which reliable charge density values could be derived. Effects of pH and ionic strength were also briefly investigated. For cationic polyelectrolytes (copolymers of acrylamide and dimethylaminoethy] acrylate), there was some loss of charge at higher pH values, probably as a result of hydrolysis. Increasing ionic strength causes a less distinct color change of o-Tb, as a result of weaker electrostatic interactions.

Tailor-modified starch/cyclodextrin-based polymers for use in tertiary oil recovery

Polymer injection into an oil field to provide water permeability reduction has been shown to be an effective control of water production from oil wells. This method relies on adsorption of the polymer on rock walls within the pores of the reservoir and it is therefore important to consider this ability when selecting the polymer to inject. In this paper the role of charge density and molecular weight on modified cationic polysaccharides has been studied to determine the proper combinations of each to provide the enhanced adsorption. The adsorption tests were preformed using colloidal titration on a range of core or rock samples taken from oil wells in Saskatchewan in an attempt to reveal the structure–property relation. Three commercial cationic starches along with two self-modified starches were studied. Apart from cationic starches a novel branched polymer based on cyclodextrin was also evaluated for its adsorption on the rock sample with well-defined structure.