Characterization of viscose fibers modified with 6-deoxy-6-amino cellulose sulfate

Cellulose viscose fibres were functionalized by novel amino cellulose sulfates (ACS), namely 6-deoxy-6-(ω-aminoethyl) amino cellulose-2,3(6)-O-sulfate (AECS), and 6-deoxy-6-(2-(bis-N′,N′-(2-aminoethyl)aminoethyl)) amino cellulose-2,3(6)-O-sulfate (BAECS). In this way an amphoteric characteristics were introduced onto cellulose viscose fibers which is extremely important by fiber applications. Whilst cellulose fibers possess only negligible carboxyl groups’ content, the coating of fibers by AECS and BAECS, respectively, introduces new functional groups to the fibers; as positively-charged amino groups and negatively-charged sulfate groups. The typical functional groups within the non-coated fibers, as well in the ACS-coated fibers, were characterized by means of X-ray photoelectron spectroscopy, conductometric-, potentiometric and polyelectrolyte titrations, as well as conventionally by the spectroscopic methylene-blue method. The electro-kinetic behavior was evaluated by measuring the zeta-potential of the fibers as a function of pH. The amounts of the positive-charges (introduced protonated amino groups) determined by potentiometric titration agreed with the amounts of the positive charges determined by conductometric titration. The total amounts of negatively-charged fiber groups (sulfate and carboxyl) determined by polyelectrolyte titration were 38.8 and 32.1 mMol kg^?1 for AECS-Vis and BAECS-Vis, respectively, and these results were in accordance with the conventional methylene-blue method.     

On the indirect polyelectrolyte titration of cellulosic fibers. Conditions for charge stoichiometry and comparison with ESCA

The effect of electrolyte (NaHCO3) concentration on the adsorption of poly-DADMAC (poly-diallyldimethylammonium chloride) onto cellulosic fibers with different charge profiles was investigated. Surface carboxymethylated fibers were obtained by grafting carboxymethyl cellulose (CMC) onto the fiber surface and bulk carboxymethylated fibers were obtained by reacting the fibers with monochloroacetic acid. It was shown that nonionic interactions do not exist between cellulose and poly-DADMAC, rather electrostatic interactions govern the adsorption. Charge stoichiometry prevails under electrolyte-free conditions, whereas surface charge overcompensation occurs at higher electrolyte concentrations. It was shown that charge stoichiometry prevails if the thickness of the electric double layer kappa(-1) was larger than the mean distance between the charges on the fiber surface, as predicted by polyelectrolyte adsorption theories, taking lateral correlation effects into account. In a second set of experiments the ESCA technique served to independently calibrate the polyelectrolyte titrations for determining the surface charge of cellulosic fibers. Various molecular masses of poly-DADMAC were adsorbed to carboxymethylated fibers having different charge profiles. The adsorption of low M(w) poly-DADMAC (7.0 x 10(3)), analyzed by polyelectrolyte titration, was about 10 times higher than that of the high M(w) poly-DADMAC (9.2 x 10(5)). Despite the difference in accessibility of these two polyelectrolytes to the fiber cell wall, ESCA surface analysis showed, as expected, only slight differences between the two polyelectrolytes. This gives strong credibility to the idea that surface charge content of cellulosic fibers can be analyzed by means of adsorption of a high-molecular-mass cationic polymer, i.e., by polyelectrolyte titration.     

Titrimetric methods for the determination of surface and total charge of functionalized nanofibrillated/microfibrillated cellulose (NFC/MFC)

Total and surface charge of three different carboxymethylated nanofibrillated/microfibrillated cellulose (NFC/MFC) samples were investigated by using titrimetric methods (conductometric and polyelectrolyte (PE) titrations). Conductometric titration was found to be suitable method for the NFC total charge measurements when the back titration with HCl was applied. Surface charge measurements of NFC/MFC were conducted by using both indirect and direct PE titrations. The direct PE titration was found to be a more suitable method for the surface charge determination of NFC/MFC whereas the indirect PE titration produced too high surface charge values. This is presumably due to kinetically locked polyelectrolyte conformations on the NFC/MFC surfaces or entrapment of residual polymer after adsorption onto the NFC/MFC gel network. Finally, NFC was propargyl-functionalized and the changes in surface and total charge were successfully monitored and compared to those of propargyl-functionalized pulp. A good correlation between the titrimetric methods and elemental analysis was observed.     

Ion binding to polyelectrolytes: Monte Carlo simulations versus classical mean field theories

The influence of ion size and surface charge model in titrations of ionizable polyelectrolytes is studied by means of the Semi Grand Canonical Monte Carlo simulation method in the context of the primitive model. Three models describing a discrete distribution of charged functional groups on the polyelectrolyte and different values for the radius of the background electrolyte spanning from ionic to hydrated radii values were analyzed. The polyelectrolyte titrations were simulated by calculating the degree of ionization versus pH curves at two ionic strengths. The results allow us to quantify the impact of the sizes of the background salt ions and surface functional groups of the polyelectrolyte on the dissociation degree. This influence is explained in terms of the effectiveness of the screening of the charged surface sites. Finally, by comparison with the Non-Linear Poisson–Boltzmann model, the influence of ionic correlations and finite size of the solution ions is assessed.     

Analysis of the oxidation of cellulose fibres by titration and XPS

The purpose of this study was to evaluate the effect of selective oxidation on the surface properties of cotton cellulose fibres. Four different methods to evaluate the accessibility, nature and content of ionisable acidic groups (charge) in the fibres were applied: potentiometric and conductometric titrations, polyelectrolyte adsorption and X-ray photoelectron spectroscopy (XPS). The results from this combination of methods show that two processes take place when the oxidation method is applied: elimination of low molecular mass non-cellulosic compounds and formation of new acidic groups in the cellulose chains. Which of these processes is predominating depends on oxidation time, but the first one is initially more important. Polyelectrolyte adsorption and XPS show that the surface concentration of acidic groups is considerably lower than the bulk concentration, i.e. during oxidation the content of carboxyl groups in the surface region decreases, while it increases in amorphous regions. The decrease is due to the dissolution of low molecular weight compounds; the increase is due to the formation of new acidic groups. The use of titration methods in combination with XPS appears to be a very useful tool for identification of the formation and distribution of ionic groups in cotton fibres and their surfaces.     

Conductometric and potentiometric titrations of nitrogen bases in non-aqueous solvents

This paper describes an experimental study of the conductometric and potentiometric titrations of nitrogen bases in non-aqeous media. It is shown that for bivalent bases the factors governing the shape of the titration curve are the same as those previously found for dibasic acids, viz. solvent, acid anion, temperature, and distance between basic groups. With the aid of this knowledge a new indifferent solvent system for potentiometric titrations has been developed, which is very attractive for the analysis of mixtures of bases.     

The fiber charge measurement depending on the poly-DADMAC accessibility to cellulose fibers

Cellulose fiber charge is a significant parameter for porous cellulose fibers, and strongly affects the swelling ability of cellulose fibers and the properties of cellulose-based materials as well. Actually, it includes surface charge and inner charge. The surface charge is mentioned often in papermaking wet-end chemistry, however, the inner charge or the total charge is paid less attention to. In this study, the cationic polydiallyldimethyl ammonium chloride (poly-DADMAC) with different molecular weight (Mw) was applied for the accessibility evaluation to the cellulose fiber charges by using polyelectrolyte adsorption technique. Results showed that higher fiber charge was detected by lower Mw poly-DADMAC (7.5–15 kDa) due to its highly efficient penetration into the fiber cell walls and neutralization with inner charges, while lower fiber charge was obtained by using higher Mw poly-DADMAC (higher than 100 kDa) because of its adsorption onto fiber surface. As a consequence, high-Mw poly-DADMAC was used to determine the surface charge of cellulose fibers, and low-Mw poly-DADMAC could be used to measure the total charge under the saturated adsorption and low ionic strength (or salts concentration). This was confirmed by SEM–EDS analysis. The low-Mw poly-DADMAC adsorption had a good agreement with conventional conductometric titration, and a linear regression equation with slope of 1.03 and regression coefficient of 0.99 was obtained.     

Use of a NICA-Donnan approach for analysis of proton binding to a lignocellulosic substrate extracted from wheat bran

The acid-base properties of a lignocellulosic substrate extracted from wheat bran have been investigated. The lignocellulosic substrate was first studied by use of FTIR, XPS, and solid-state 13C NMR to characterize the surface-active groups. Major contributions arise from the presence of carboxylic and phenolic sites. The former are associated with long-chain fatty acids and the latter are constituent units of lignin. All ionizable sites were quantified by use of the Ca-acetate method and by potentiometric titrations in non-aqueous media. Results were compared with those from conductimetric titrations in water and in the presence of barium ions. Protometric titration curves for the lignocellulosic substrate were obtained at several ionic strengths. Data were also treated with the NICA-Donnan model to determine the intrinsic ionization parameters.     

Coupled chemical processes at clay/electrolyte interface: a batch titration study of Na-montmorillonites

The present work addresses the protolytic charge of montmorillonite, which occurs on the broken-bond sites at the particle edges. The purpose is to overcome the general difficulty arising in potentiometric titration due to coupled side reactions, which severely impede the titrant budget (partial dissolution of the clay and of secondary phases, hydrolysis and readsorption of dissolved species, cation exchange). Batch potentiometric titrations were carried out on the montmorillonite fractions extracted from two bentonites (MX80 and SWy2) to quantify their protolytic charge. The effects of equilibration time (24 h and 7 days), pH from 4 to 10, and ionic strength (0.1 and 0.01 mol L(-1)) were extensively studied for the MX80 sample. Quantification of dissolution was achieved by analysis of the equilibrium solutions for dissolved species and by La(3+) exchange of the readsorbed species. The results clearly show that secondary phases such as iron- or silica-rich minerals contribute to the dissolved species, according to the nature of the raw bentonite. Furthermore, readsorption affects significant amounts of dissolved species. The overconsumption of proton/hydroxide due to dissolution, readsorption, and hydrolysis of dissolved species was evaluated using a self-consistent thermodynamic calculation. The ability of such calculation to correct the raw titration curves in order to extract the titrable surface charge of montmorillonite was evaluated by comparison with the continuous titration procedure. Especially in the alkaline domain, correcting the raw batch titration curves for the measured side reactions failed to reproduce the continuous titration curves. These observations demonstrate the limitations of the batch titration method and the superiority of fast, continuous methods for quantifying the dissociable surface charge of clays.     

水溶性高分子链中磺酸盐基团含量的电导滴定测定法

研究了N ,N ,N 三甲基十六烷基溴化铵 (CTAB)与丙烯酰胺 (AM) 2 丙烯酰胺基 2 甲基丙磺酸钠盐(NaAMPS)二元共聚物P(AM co NaAMPS)的复合作用 .在复合作用过程中 ,由于不断释放出高导电性的无机盐小离子 ,故随着表面活性剂的加入 ,聚电解质水溶液的电导率不断增大 .当采用较低浓度 (0 0 0 1mol·L- 1 )且使二者的离子等摩尔量发生复合作用时 ,体系的电导率会发生明显的转折 .利用电导率的这一转折性变化 ,建立起了复合作用电导滴定法测定共聚物P(AM co NaAMPS)分子链中磺酸盐单体NaAMPS含量的新方法 .与元素分析进行比较的结果表明 ,上述复合作用电导滴定法可作为测定水溶性大分子链中磺酸盐单体含量的方便而又准确的方法 ,而且预计还可用作为测定水溶性大分子链中其它离子性基团含量的简捷方法     

Some observations on catalytic conductometric titrations

Conductometric and high-frequency conductometric methods for the determination of the endpoint of catalytic titrations were developed. Titrations of sodium acetate were made in a mixture of acetic anhydride and acetic acid (7:3–11:3) which was 0.05–0.1 mol dm⁻³ in sodium perchlorate. Integral and derivative titration curves were recorded in both coulometric and volumetric titrations. Different acylation reactions, as well as dehydration of formic acid, were used as the indicator reactions. The optimal conditions of determination—choice of volume ratio of acetic anhydride to acetic acid, rate of the titrating reagent addition, concentration of sodium perchlorate, and concentration of several alcohols, water, and formic acid as components of the indicator reactions—were determined. Using the catalytic conductometric method, amounts of 0.04–11 mg of sodium acetate were determined with a relative standard deviation of less than 0.8 and 1.6% in volumetric and coulometric addition, respectively. Using the catalytic high-frequency conductometric method, amounts of 1–11 mg of sodium acetate were determined with relative standard deviation less than 0.5% (volumetrically) or less than 1.4% (coulometrically). The obtained results were compared with those of potentiometric and catalytic thermometric titrations.     

Determination of Point of Zero Charge of Tunisian Kaolinites by Potentiometric and Mass Titration Methods

This paper deals with determining points of zero charge of natural and Na⁺‐saturated mineral kaolinites using two methods: (1) acid‐base potentiometric titration was employed to obtain the adsorption of H⁺ and OH^? on amphoteric surfaces in solutions of varying ionic strengths in order to determinate graphically the point of zero net proton charge (PZNPC) defined equally as point of zero salt effect (PZSE); (2) mass titration curve at different electrolyte concentrations in order to estimate PZNPCs by interpolation and to compare with those determined by potentiometric titrations. The two methods involved points of zero charge approximately similar for the two kaolinites between 6.5‐7.8, comparable to those reported previously and were in the range expected for these clay minerals. The comparison of potentiometric surface titration curves obtained at 25 °C and those published in the literature reveals significant discrepancies both in the shape and in the pH of PZNPCs values.     

Swelling behaviour of succinylated fibers

The swelling behaviour of cellulosic fibers bearing various amounts of carboxylic groups introduced by succinylation was studied as a function of pH. Upon an increase of pH, the perimeter of the succinylated fibers expanded as measured with the Wilhelmy plate technique. The fibers pass two pH regimes of increased expansion, pH = 5 and pH = 9. These pH levels correlate with the conductometric titration, which reveals two inflection points in both the pH and conductivity values for the succinylated fibers. Determinations of fiber saturation points (FSP) confirm that the cell wall is largely affected by increased pH. Analysis of the fibers with ESEM (Environmental Scanning Electron Microscope) showed that bundles of fibrils were released from the surface of the succinylated fibers at higher pH. Wilhelmy measurements also showed that the surface roughness was more than doubled in fibers succinylated for 12 h as pH rose from 3.2 to 10. These results indicate that, as the charge of the fibers is increased, the swelling forces reach such levels of magnitude that they overcome the structural network forces holding the fiber wall together. The methodology applied can hence be used to quantify the fundamental gel properties of the fiber wall.     

Emulsifier-free emulsion polymerization of tetrafluoroethylene by radiation. V. Effect of reaction conditions on the stability of polytetrafluoroethylene latex

The stability of PTFE latex prepared in the absence of emulsifier by radiation-induced polymerization was investigated by electrophoresis and conductometric titration. The storage stability depends on total dose rather than dose rate, and the stable latex can be obtained in the region log D > 0.026 V₁ ? 0.6, where D is the total dose (10⁴ rad) and V₁ is a polymer concentration in latex (g/liter). The stability increases only during polymerization in the presence of enough TFE monomer. The ζ potential of the latex particles lies in the region from ?25 to ?50 mV in an as-polymerized state (near pH 3) and from ?50 to ?65 mV at pH 10. The number of carboxyl end groups and surface charge density were examined by conductometric titration with NaOH and calculation from the G values of radiolysis of water. All the surface charge densities measured by conductometric titration are larger than those calculated from the G values. These results suggest that some acids have been formed on the surface of the particles. The acids may be the carboxyl end groups of polymer chains or hydrofluoric acid (HF) adsorbed on the surface. PTFE particles prepared in this polymerization system are stabilized mainly due to the carboxyl end groups and adsorptions of OH? and HF on the particles.     

Determination of acidic sites and binding toxic metal ions on cumin surface using nonideal competitive adsorption model

A fundamental study of the application of cumin biomass in the recovery of Cu and Zn metal ion uptake from food and drinks is carried out at different pH's and at fixed ionic strength. The chemical characteristics of protein in cumin seeds were investigated. Results showed that cumin contains 18.25% crude protein, which includes 18 amino acids. The main reactive groups on protein cumin are amino and carboxylic groups of dicarboxylic amino acids, leading to a pH-dependent charge. Therefore, the cumin surface is considered as a heterogeneous system. To describe protonation behavior in a heterogeneous cumin biomass (cumin/0.1 M NaNO(3)) system, acid-base titrations have been performed with conductometric and potentiometric titration. Measurement of the reactivity of cumin surface in the adsorption of Cu and Zn metal ions and determination of metal binding at different pH's were also carried out. To solve broad and ill-defined titration curves, a simplified version of nonideal competitive analysis (NICA) by Plette et al.) was applied. The results show that the sorption of the bivalent metal ions onto the whole surface of cumin could be attributed to a monodentate binding to one site mainly carboxylic-type site.     

Evaluating alternative electrostatic potential models for polyacrylamide-co-acrylate in aqueous solution

The capabilities of three simplified analytical equations to accurately model electrostatic interactions during proton binding and release by linear anionic polyelectrolytes in aqueous solution were evaluated. The impermeable sphere (IS), Donnan (DN), and cylindrical (CY) electrostatic models were fit to experimental acid-base titration curves of linear polyacrylamide-co-acrylate having ionizable site densities ranging from ca. 10-35%. The titrations were conducted in 0.003-0.12M NaCl solutions and the sum of squared errors from modeled and experimental data was used as a comparative index of each model's capability. In addition, the relative size of each polyelectrolyte was estimated from its measured specific viscosity and then compared against the values obtained from the fitting procedure for the size parameter that each model contained. Although the IS and DN electrostatic models could be used to obtain reasonably good fits to each titration curve, the size parameter values obtained by each model were not reflective of the actual polyelectrolyte sizes, indicating that the models had limited physical meaning and that the size parameter was essentially just an additional fitting parameter in each model. In contrast, the CY model was not only more effective in its ability to fit the titration data but also provided a better physical representation of the polyelectrolyte size. Therefore, for polyelectrolytes that remain essentially linear or are only loosely coiled such that counter ions are free to travel throughout the polymer structure, we conclude that the CY model and its morphological representation of a cylindrical polyelectrolyte are more valid and realistic than the IS and DN models and their representation of polyelectrolytes as spheres.     

Pristine Points of Zero Charge of Gallium and Indium Oxides

Electrokinetic measurements and potentiometric titrations of indium oxide (commercially available reagent grade powder, washed with NaOH and HNO(3) to remove strongly adsorbed species) indicate the pristine point of zero charge to be pH 8.7. The isoelectric point at pH 9 was obtained for gallium oxide prepared in the same way. These values match the pristine point of zero charge of alumina, but they are much higher than the values reported for indium oxide and gallium oxide in the literature. Copyright 2001 Academic Press.     

A modified Poisson-Boltzmann model including charge regulation for the adsorption of ionizable polyelectrolytes to charged interfaces, applied to lysozyme adsorption on silica

The equilibrium adsorption of polyelectrolytes with multiple types of ionizable groups is described using a modified Poisson-Boltzmann equation including charge regulation of both the polymer and the interface. A one-dimensional mean-field model is used in which the electrostatic potential is assumed constant in the lateral direction parallel to the surface. The electrostatic potential and ionization degrees of the different ionizable groups are calculated as function of the distance from the surface after which the electric and chemical contributions to the free energy are obtained. The various interactions between small ions, surface and polyelectrolyte are self-consistently considered in the model, such as the increase in charge of polyelectrolyte and surface upon adsorption as well as the displacement of small ions and the decrease of permittivity. These interactions may lead to complex dependencies of the adsorbed amount of polyelectrolyte on pH, ionic strength, and properties of the polymer (volume, permittivity, number, and type of ionizable groups) and of the surface (number of ionizable groups, pK, Stern capacity). For the adsorption of lysozyme on silica, the model qualitatively describes the gradual increase of adsorbed amount with pH up to a maximum value at pHc, which is below the iso-electric point, as well as the sharp decrease of adsorbed amount beyond pHc. With increasing ionic strength the adsorbed amount decreases (for pH > pHc), and pHc shifts to lower values.     

Supramolecular Systems from Natural Polymers and Maleic Polyelectrolytes

Summary: The formation of polyelectrolyte complexes by interaction between chitosan and maleic acid copolymers as strong/weak dibasic polyanions was investigated. The interaction between the sodium salt of maleic acid copolymers with styrene or vinyl acetate and the chitosan hydrochloride in aqueous solution was followed by potentiometric, conductometric and turbidimetric titration. The effect of the added low molecular salt on the complex formation was also investigated. The precipitated complexes were analyzed by FTIR spectroscopy and TG analysis. Preliminary layer-by-layer deposition experiments were performed to obtain thin films.     

Characterization of the cell surface and cell wall chemistry of drinking water bacteria by combining XPS, FTIR spectroscopy, modeling, and potentiometric titrations

Aquabacterium commune, a predominant member of European drinking water biofilms, was chosen as a model bacterium to study the role of functional groups on the cell surface that control the changes in the chemical cell surface properties in aqueous electrolyte solutions at different pH values. Cell surface properties of A. commune were examined by potentiometric titrations, modeling, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. By combining FTIR data at different pH values and potentiometric titration data with thermodynamic model optimization, the presence, concentration, and changes of organic functional groups on the cell surface (e.g., carboxyl, phosphoryl, and amine groups) were inferred. The pH of zero proton charge, pH(zpc) = 3.7, found from titrations of A. commune at different electrolyte concentrations and resulting from equilibrium speciation calculations suggests that the net surface charge is negative at drinking water pH in the absence of other charge determining ions. In situ FTIR was used to describe and monitor chemical interactions between bacteria and liquid solutions at different pH in real time. XPS analysis was performed to quantify the elemental surface composition, to assess the local chemical environment of carbon and oxygen at the cell wall, and to calculate the overall concentrations of polysaccharides, peptides, and hydrocarbon compounds of the cell surface. Thermodynamic parameters for proton adsorption are compared with parameters for other gram-negative bacteria. This work shows how the combination of potentiometric titrations, modeling, XPS, and FTIR spectroscopy allows a more comprehensive characterization of bacterial cell surfaces and cell wall reactivity as the initial step to understand the fundamental mechanisms involved in bacterial adhesion to solid surfaces and transport in aqueous systems.