On the influence of surfactants on the adsorption of polysaccharide-based polymers on cotton studied by means of fluorescence spectroscopy

In this study, we examined the influence of surfactants on the adsorption of polymers on cotton fibers. The extent of polymer adsorption on cotton was determined directly by means of fluorescence spectroscopy using fluorescently labeled polymers. The investigation of polymer adsorption in the presence of different types of surfactants and for a large range of differently structured polymers allows us to obtain a rather general picture of this important issue. Systematic relationships between the presence of surfactant and the type of polymer can be deduced but cannot be cast in simple terms such as electrostatic interaction but instead depend on the detailed interaction between the surfactant and polymer both in solution and adsorbed on the cotton surface. A particularly complex situation arises for the case of oppositely charged surfactant and polymer because of the possibility of precipitate formation. The study of such complex systems not only is of scientific interest but also is of great commercial interest because both polymers and surfactants are parts of detergent formulations and cotton is one of the most abundantly used materials for fabrics.     

Kinetics of adsorption of polyvinylamine on cellulose fibers. I. Adsorption from salt-free solutions

Adsorption of fully hydrolyzed polyvinylamine on cellulose fibers in the short term was investigated by supplying the polymer to the fibers, first instantaneously by pouring the polymer solution into a jar containing the fiber dispersion (jar experiments) and second, at controlled rates (the reactor experiments). In the latter case, the rate of supply of polymer to the fiber dispersion confined in the reactor was monitored by setting the concentration of the solution being injected at a controlled rate. The concentration of the polymer solution exerts a paramount influence on the kinetics of adsorption and on the amount of polymer adsorbed at (or near) fiber surface saturation, while the rate of polymer supply only plays a minor role. The main observation is the emergence of two types of polymer layers corresponding to diffuse and dense layers. The former were characterized by adsorption layers of density smaller than 0.65 mg/g cellulose that are composed of adsorbed polymers having sustained extended flattening in the adsorbed state. The latter reach densities as high as 10 mg/g cellulose when the fiber surface is fully coated, thus indicating that reconformation is limited or even impeded at short terms. The threshold adsorption corresponds more or less to equilibrated layers, since the final coverage determined at adsorption equilibrium did not exceed 0.6 to 0.7 mg/g cellulose.     

Quantitative analysis of cationic poly(vinyl alcohol) diffusion into the hairy structure of cellulose fiber pores: charge density effect

The diffusion of charged polymers into the pores of cellulose fibers has not yet been fully understood due to the complexity of the interaction between polymers and fibers. In this paper, the diffusion of cationic-modified poly(vinyl alcohol) (CPVA) with tailored charge densities and a relatively high molecular weight into the pores of bleached aspen high-yield pulp (via a chemi-thermomechanical pulping process) was quantitatively investigated via an adsorption analysis, charge density analysis, and solute exclusion technique (SET). The results showed that the adsorption of the low-charged CPVA was substantially higher than that of the high-charged CPVA on fibers. The surface charge density analysis confirmed that approximately 17 mg/g of the high-charged CPVA adsorbed on the outer surface and on the macropores of fibers and the remaining (23 mg/g) diffused into the pores. The SET analysis confirmed that the pore size of fibers was more significantly reduced by applying the low-charged CPVA than the high-charged one. The influencing factors for the diffusion of CPVA into the large and small pores were related to the repulsion force developed between the adsorbed polymers and approaching polymers, entropy increase, and the polymer flexibility. The Brunauer-Emmett-Teller surface area analysis showed an increase in the surface area of fibers upon CPVA adsorption. It was proposed that the diffused CPVA prevented complete fiber pore collapse during drying, which eventually increased the surface area of fibers.     

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.     

Electrokinetic properties of processed cellulose fibers

Natural cellulose fibers (cotton) comprise several noncellulose compounds (hemicellulose, wax and pectin substances) and cationic impurities which cause problems during different adsorption processes such as dying, or final fiber finishing and coating. Therefore the chemical purification (NaOH boiling, enzymatic purification, demineralization, extraction or oxidative bleaching) is the most important step in cellulose textile finishing. Alternative ways to describe the success of different processes in fiber purification which result in distinct surface charge and hydrophilicity are the determination of electrokinetic properties and the water uptake of textile fibers. The zeta-potential (ζ) was determined by streaming potential measurement as a function of the pH. From the ζ–pH functions the adsorption potential for all ionic species Φ_i (i.e. ( , in the case of potassium chloride solutions), the charge densities σ^k and the pK values are calculated according to the Börner and Jacobasch model.

The degradation and removal of hydrophobic noncellulose compounds which cover the primary hydroxyl and carboxyl groups of the cellulose polymer is clearly shown by an increase of the negative ζ of the plateau, which is in good agreement with the electrokinetic parameters of cotton samples determined by the Börner and Jacobasch model. The electrokinetic parameters determined by the Börner and Jacobasch model can be used to describe the adsorption/dissociation ability of textile fibers. The progress of the fiber processing (cleaning) is reflected by the surface charge as well as the hydrophilicity of the fiber.     

The adsorption of cationic and amphoteric copolymers on glass surfaces: zeta potential measurements,adsorption isotherm determination,and FT Raman characterization

The adsorption of cationic and amphoteric copolymers onto controlled pore glass (CPG) powders has been studied by measurement of the powder particle zeta (zeta) potential, by determination of the adsorption isotherm, and by FT Raman measurements of the polymer-coated powder. The cationic polymers consisted chiefly of homopolymers of dimethyldiallylammonium chloride (DMDAAC) or copolymers of DMDAAC and acrylamide. The amphoteric polymers studied included copolymers of DMDAAC and acrylic acid. The comonomer ratio was varied to explore the dependence of cationic charge density on the extent and effect of adsorption. Both types of polymers adsorb onto the anionic glass surface via an ion-exchange mechanism. Consequently, a correspondingly higher mass of a low-charge-density copolymer adsorbs than of a cationic homopolymer. The presence of the anionic portion in the amphoteric polymers does not significantly alter this picture. The zeta potential, however, reflects the overall nature of the polymer. Cationic polymers effectively neutralize the glass surface, while amphoteric polymers leave the zeta potential net negative. Adsorption isotherms, determined via the depletion technique using colloidal titration, were used to "calibrate" a FT Raman method. The latter was used to determined the amount of adsorbed polymer under solution conditions in which colloidal titration could not be performed.     

Hydrodynamically induced formation of cellulose fibers. I. Observations on the formation of cellulose fibers from stirred solutions

Like synthetic polymers, a natural polymer such as cellulose may crystallize in fibrous form from stirred solutions. In the present work, it is demonstrated that cellulose fibers can be formed by precipitation from dimethyl sulfoxide/paraformaldehyde solutions by two methods that involve different mechanisms of fiber formation, viz., (A) precipitation of cellulose by addition of nonsolvent to the stirred cellulose solution, and (B) precipitation of cellulose by coagulation of droplets of cellulose solution in a stirred precipitant. Both processes yield fibers with properties depending on the stirring speed and the coagulant strength. The molecular orientation and tensile strength of the fibers produced by method A was low, but increased with the stirring speed, while some fibers formed by method B reached extremely high orientation, depending on the thickness of the fibers. The two mechanisms of fiber formation are discussed on the basis of the experimental observations.     

Charge reversal system with cationized cellulose nanocrystals to promote dewatering of a cellulosic fiber suspension

A surface-modified form of cellulose nanocrystals (CNC) was employed to explore mechanisms related to the release of water from cellulosic fiber suspensions during papermaking. The CNC surface was rendered partly cationic (forming CCNC) by adsorption of poly-(diallyldimethylammonium chloride) (poly-DADMAC), a high charge density cationic polymer. Meanwhile, a suspension of cellulosic fibers and calcium carbonate particles was prepared from recycled copy paper, which was treated sequentially with poly-DADMAC and a very-high-mass anionic acrylamide copolymer (aPAM). Subsequent addition of CCNC strongly promoted water release, whereas ordinary CNC had the opposite effect. The effect of the CCNC was achieved with ten times less poly-DADMAC, as the final additive, compared to when adding the polymer alone. Results were consistent with a model of nanoparticle-enabled bridging, based on an assumption of non-equilibrium or slowly equilibrating processes of adsorption.     

Aluminum Oxide Coated Cellulose Fibers Modified with n-Propylpyridinium Chloride Silsesquioxane Polymer: Preparation, Characterization, and Adsorption of Some Metal Halides from Ethanol Solution

Aluminum oxide coated cellulose fibers were modified, by an impregnation procedure, with n-propylpyridinium chloride silsesquioxane polymer. Good adherence of the polymer to the surface of modified cellulose fibers was obtained due to the Al-O-Si bond formation. The metal X-ray mapping showed that aluminum oxide and the silsequioxane polymer (Al and Si mapping) are highly dispersed on the fiber's surface. The ion exchange capacity of the material, determined on basis of exchangeable chloride ions, was 1.1 mmol g-1. The adsorption isotherms of FeCl3, CuCl2, and ZnCl2 from ethanol solutions were determined for each metal. The adsorption capacities were (in mmol g-1): FeCl3 = 0.82, CuCl2 approximately ZnCl2 = 0.37. The metal ions are adsorbed as anionic complex species by the following equilibrium reaction: + MCln right arrow over left arrow Copyright 1999 Academic Press.     

Adsorption and inactivation behavior of horseradish peroxidase on cellulosic fiber surfaces

The physical immobilization behavior of horseradish peroxidase (HRP) on cellulosic fiber surfaces was characterized using adsorption and inactivation isotherms measured by the depletion method followed by fitting of Langmuir’s and Freundlich’s models to the experimental data. The adsorption and inactivation behavior of simpler and relatively non-porous high and low crystalline cellulosic substrates (microcrystalline cellulose and regenerated cellulose) as well as more complex and porous cellulosic pulp fibers (bleached kraft softwood fibers) were investigated. The effect of the sorbent surface energy on HRP adsorption was demonstrated by increasing the hydrophobicity of the cellulosic fibers using an internal sizing agent. The influence of the fiber surface charge density on HRP adsorption was studied via modification of the cellulosic fibers using TEMPO (2,2,6,6-tetramethyl-1-piperidiniloxy radical)-mediated oxidation methods. Results showed that hydrophobic interactions had a much larger effect on HRP adsorption than electrostatic interactions. More hydrophobic fiber surfaces (lower polar surface energy) result in larger enzyme-fiber binding affinity constants and higher binding heterogeneity. It was also found that oxidation of the cellulosic fiber substrate reduces enzyme adsorption affinity but significantly increases the loading capacity per unit weight of the surface.     

The effect of the amphiprotic nature of human hair keratin on the adsorption of high charge density cationic polyelectrolytes

Adsorption of the cationic polymers poly(methacrylamidopropyltrimethyl ammonium chloride) (PMAPTAC) and poly(1,1-dimethylpiperidinium-3,5-diallylmethylene chloride) (PDMPDAMC) on human hair was studied by measurements of the amount of polymer adsorbed and by the streaming potential method. Results reflect the amphoteric nature of the keratin surface and show that the excess of anionic sites at pH values above 4 is the main driving force for the adsorption of cationic polyelectrolytes. Lowering the pH below 4 or addition of neutral salt (KCl) reduces the amount of adsorbed polymer. It was shown that the adsorption of cationic polymer in the concentration range 0.01 to 0.1 % and at neutral pH reverses the overall character of the surface from anionic to cationic. Keratin fibers modified in this manner do not exhibit amphoteric character and bear excess positive charge in the pH range 2–9.5. The value of the amount of the polymer adsorbed at saturation concentration (2 mg/g) as well as the lack of molecular weight effect in the range (5 · 10⁴ – 10⁶) on the amount of polymer adsorbed suggest that polymer chains adopt a rather extended conformation on the fiber surface. Some data concerning the formation of a complex between adsorbed cationic polymer and anionic detergents or polyelectrolytes are also presented.     

Adsorption of anionic surfactant on porous and non-porous polyethylene terephthalate films

We study the adsorption of anionic surfactant, sodium dodecyl diphenyloxide disulfonate (SDDD) on three types of polyethylene terephthalate substrates from aqueous solutions of SDDD of different concentrations. Neutral electrolyte (KCl) was added to the solutions to vary the ionic strength. The three types of substrates were: (1) original polymer film, (2) etched non-porous film, which was obtained from pristine film by chemical etching and bears negative charge on the surface, (3) etched porous membranes, which were fabricated from pristine film by ion irradiation and subsequent chemical etching. The membranes have negative charge on the flat surface and on the inner pore walls. The comparison of original and etched nonporous films shows that the negative charge on the flat surface has weak effect on adsorption of the anionic surfactant. The comparison of etched non-porous and porous films shows that the SDDD adsorption on the inner walls of pores is much weaker than on flat surface—even in case the pore radius is significantly larger than the Debye length. This “exclusion” effect strongly depends on ionic strength of solution. For the porous films, the effect of the pore size and shape on the anionic surfactant adsorption is presented and discussed.     

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.     

Adsorption of cationic cellulose derivative/anionic surfactant complexes onto solid surfaces. II. Hydrophobized silica surfaces

The effect of the anionic surfactant SDS (sodium dodecyl sulfate) on the adsorption behavior of cationic hydroxyethyl cellulose (Polymer JR-400) and hydrophobically modified cationic cellulose (Quatrisoft LM-200) at hydrophobized silica has been investigated by null ellipsometry and compared with the previous data for adsorption onto hydrophilic silica surfaces. The adsorbed amount of LM-200 is found to be considerably larger than the adsorbed amount of JR-400 at both surfaces. Both polymers had higher affinity toward hydrophobized silica than to silica. The effect of SDS on polymer adsorption was studied under two different conditions: adsorption of polymer/SDS complexes from premixed solutions and addition of SDS to preadsorbed polymer layers. Association of the surfactant to the polymer seems to control the interfacial behavior, which depends on the surfactant concentration. For the JR-400/SDS complex, the adsorbed amount on hydrophobized silica started to increase progressively from much lower SDS concentrations, while the adsorbed amount on silica increased sharply only slightly below the phase separation region. For the LM-200/SDS complex, the adsorbed amounts increased progressively from very low SDS concentrations at both surfaces, and no large difference in the adsorption behavior was observed between two surfaces below the phase separation region. The complex desorbed from the surface at high SDS concentrations above the critical micelle concentration. The reversibility of the adsorption of polymer/SDS complexes upon rinsing was also investigated. When the premixed polymer/SDS solutions at high SDS concentrations (>5 mM) were diluted by adding water, the adsorbed amount increased due to the precipitation of the complex. The effect of the rinsing process on the adsorbed layer was determined by the hydrophobicity of the polymer and the surface.     

The influence of classical and enzymatic treatment on the surface charge of cellulose fibres

Natural cellulose fibres comprise several non-cellulose compounds and cationic trash which cause problems during different adsorption processes such as dying, printing, final fiber finishing and coating. Therefore the pre-treatment (classical NaOH or environmental friendly enzymatic treatment, demineralisation) is the most important step in cellulose textile prefinishing-cleaning. An appropriate way to describe the success of different processes in fiber pre-treatment which result in distinct surface charge is the determination of electrokinetic properties-zetapotential (ZP) of fibers and textile materials. The zetapotential was determined by streaming potential measurements as a function of the pH and the surfactant concentration in the liquid phase.Cellulose fibers in an aqueous medium are negatively charged due to their characteristic carbonyl and hydroxyl groups. The degradation and removal of specific hydrophobic non-cellulose compounds which cover the primary wall of the cellulose polymer change the surface charge.The ZP is mainly influenced by waxes, their removal decreases the negative ZP. This result is obtained by the classical chemical process as well as by an environmentally friendly enzymatic treatment.Our results indicate that the progress of textile treatment and purification is reflected by the zetapotential of the fabrics. This method enables the estimation of the process'es progress and the interaction between components of the liquid phase and the fibre surface.     

Influence of counterion on the interaction of dodecyl sulfates and cellulose ethers

Fluorescence probe techniques together with microcalorimetry and dye solubilization were used to study the interaction between nonionic polymers and anionic surfactants with different monovalent counterions in order to examine the effects of the counterion. The polymers used were the cellulose ethers hydroxypropyl methyl cellulose (HPMC) and ethyl hydroxyethyl cellulose (EHEC). The surfactants were dodecyl sulfates with potassium, sodium, and lithium as counterions (KDS, NaDS, LiDS). The counterion influenced the interaction start concentration as well as the nature of the mixed aggregates formed. The interaction start, according to surfactant concentration, was found to be in the order KDS < NaDS < LiDS for both polymers as well as in aqueous solution. From fluorescence measurements it was found that the KDS-polymer aggregates shield pyrene from water better than the other surfactants, indicating larger aggregates with a more fluid interior. The microcalorimetry measurements confirm that the adsorption of the surfactants onto the polymer is endothermic and entropy driven at the start and as more clusters are formed on the polymer chains the process converts to being exothermic and driven by both enthalpy and entropy.     

Adsorption of cellulose derivatives on flat gold surfaces and on spherical gold particles

The adsorption of hydroxyethylcellulose (HEC), ethyl(hydroxyethyl)cellulose (EHEC), and their hydrophobically modified counterparts HM-HEC and HM-EHEC has been studied on planar gold and citrate-covered gold surfaces by means of quartz crystal microbalance with dissipation monitoring (QCM-D), and on citrate-covered gold particles with the aid of dynamic light scattering (DLS). The QCM-D results indicate that larger amounts of polymer are adsorbed from aqueous solutions of HM-HEC and HM-EHEC on both substrates than from solutions of their unmodified analogues. The adsorption affinity for all the polymers, except EHEC, is higher on the citrate-covered surfaces than on the bare gold substrate. This indicates that more adsorption sites are activated in the presence of the citrate layer. The experimental adsorption data for all the polymers can be described fairly well by the Langmuir adsorption isotherm. However, at very low polymer concentrations significant deviations from the model are observed. The value of the hydrodynamic thickness of the adsorbed polymer layer (delta h), determined from DLS, rises with increasing polymer concentration for all the cellulose derivatives; a Langmuir type of isotherm can be used to roughly describe the adsorption behavior. Because of good solvent conditions for HEC the chains extend far out in the bulk at higher concentrations and the value of delta h is much higher than that of HM-HEC. The adsorption of EHEC and HM-EHEC onto gold particles discloses that the values of delta h are considerably higher for the hydrophobically modified cellulose derivative, and this finding is compatible with the trend in layer thickness estimated from the QCM-D measurements.     

Study on the interaction between anionic and cationic latex particles and Portland cement

The interaction between organic latex polymers and the surface of hydrating cement was investigated by measuring the zeta potential and adsorbed amount of polymer on cement. First, differently charged model latex particles were synthesized in aqueous media by well-known emulsion polymerization technique. The latex polymers were characterized by differential scanning calorimetry (DSC), dynamic light scattering (DLS) and environmental scanning electron microscopy (ESEM). Electrokinetic latex surface properties were investigated by means of streaming potential measurements using a particle charge detector (PCD). It is shown that the anionic latexes adsorb a considerable amount of Ca²⁺ from the cement pore solution. Next, adsorption of the latex polymers on the surface of hydrating cement was confirmed by zeta potential measurements using the electroacoustic method. A water to cement ratio in the cement paste as low as 0.5 was studied, representing actual conditions in mortar and concrete. Additionally, adsorption isotherms were determined in a sedimentation test using the depletion method. For all latex polymers, Langmuir type adsorption isotherms were found. The latex dosages required to achieve saturated adsorption on the cement surface obtained from zeta potential measurements correspond well with those determined in the sedimentation test. Electron microscopy photographs confirm that the charged latex polymers adsorb selectively on surface areas of hydrating cement showing opposite charge. This way, domains of organic latex polymers exist on the cement surface. They provide adhesion between the inorganic cement matrix and the organic polymer film formed later on by particle coalescence as a result of cement hydration and drying.     

Some Properties of Polyelectrolyte-G rafted Cellulose

Anionic and cationic polyelectrolytes were grafted on a bleached kraft pulp. Grafting an anionic polyelectrolyte (sodium poly-acrylate-polyacrylamide copolymer) resulted in modified fibers possessing outstanding affinity for water and saline solutions in the pH range where the polymer is ionized. Swelling is the result of both the grafting operation itself and of the presence of the ionized polyelectrolyte.

The swollen grafted fibers could be disintegrated under intense shear to give a colloidal solution exhibiting pseudoplastic thixo-tropic behavior. Electron microscopic examination revealed that during the shearing process the fiber had been disintegrated into its constitutive elements, long rodlike protofibrils, which are believed to be mainly responsible for the high viscosities observed.

Grafting a cationic polyelectrolyte (polydimethylamino ethyl methacrylate hydrochloride) produced fibers with lower but significant water swelling. The influence of pH on swelling was similar, although reversed, to that observed with the anionic grafted fibers. The presence of a large number of cationic groups in the porous cellulose fiber gel points to applications in ion-exchange and adsorption processes.     

Synthesis of a novel antimicrobial-modified starch and its adsorption on cellulose fibers: part II––adsorption behaviors of cationic starch on cellulose fibers

The adsorption of guanidine polymer modified starches on cellulose fibers was investigated along with the systematic studies on various influencing factors including temperature, pH, ionic strength and charge density of the starches. The AFM results revealed the relationship between the adhesion force and adsorption capacity. The adsorption capacity is not necessarily proportional to the adhesion force. The conditions for achieving the maximum adsorption were: temperature, 40 °C; pH, 6; C_NaCl, 0 mM and charge density, 0.4 meq/g. The corresponding the normalized adhesion force is approximate 1 mN/m. In terms of the surface roughness determined by AFM, it has been proved that adsorbed starches of high charge density tend to form train structure, whereas those of low charge density tend to form tails and loops. Due the comb molecular structure, the adsorption capacity of the novel cationic starch reaches 124.3 mg/g, which is much greater than those reported previously.