The effect of molecular weight and degree of substitution on the interactions between carboxymethyl cellulose and cetyltrimethylammonium bromide

Composites of cellulose nanocrystals in combination with either cellulose nanofibril or carboxymethylcellulose as functional packaging films

Cellulose nanocrystals (CNC) were mixed with either cellulose nanofibril (CNF) or carboxymethylcellulose (CMC) in variable proportions (0/100, 20/80, 40/60, 50/50, 60/40, 80/20 and 100/0) to obtain cast films with acceptable barrier and mechanical properties as replacements for food packaging plastics. Both CNF and CMC improved tensile strength, elongation, UV opacity, air resistance, hydrophobicity (WCA-water contact angle), water vapor transmission rate (WVTR) and oxygen impermeability in pure CNC. WVTR and oxygen permeability were strongly dependent on relative humidity (RH). Interestingly, the greatest effect on WVTR was observed at RH = 90% in films containing CMC in proportions above 60%. CMC- and CNF-containing films had oxygen impermeability up to an RH level of 80% and 60%, respectively. The previous effects were confirmed by food packaging simulation tests, where CMC-containing films proved the best performers. The composite films studied were biodegradable-which constitutes a major environmental related advantage-to an extent proportional to their content in CMC or CNF.

CTAB-modified carboxymethyl cellulose/bagasse cryogels for the efficient removal of bisphenol A, methylene blue and Cr(VI) ions: Batch and column adsorption studies

The simultaneous removal of organic and inorganic pollutants from water requires multifunctional adsorbents. Cryogels of carboxymethyl cellulose (CMC) and sugarcane bagasse (BG) were modified with cetyltrimethylammonium bromide (CTAB) micelles for the adsorption of methylene blue (MB), Cr(VI) ions and bisphenol A (BPA) separately, in binary or ternary aqueous mixtures. Batch adsorption studies of MB and Cr(VI) and BPA on the CMCBG-CTAB adsorbents indicated removal capacities of 100%, 70% and 95%, respectively. MB adsorbed as multilayers on the CMCBG walls by electrostatic interaction, whereas Cr(VI) and BPA adsorbed on the cationic CTAB micelles surface and hydrophobic core of CTAB micelles, respectively. The breakthrough curves obtained for pure adsorbates and their mixtures showed that the adsorption of Cr(VI) ions increased (i) ~ 3.5 times in binary mixture with BPA or in the ternary mixture, in comparison to pure Cr(VI) solution, and (ii) 1.4 times in binary mixture with MB molecules, due to synergistic effects. In the presence of Cr(VI) ions in binary or ternary mixtures, the adsorption of MB was dramatically reduced due to screening effects. The adsorption of BPA was not significantly affected by the presence of MB or Cr(VI). The adsorbents were recycled five times without significant efficiency loss.

Oscillatory rheology of carboxymethyl cellulose gels: Influence of concentration and pH

The flow properties of ionic polysaccharides are determined by the interplay of electrostatic and hydrophobic interactions, which depend on the ionic strength and pH of the solvent. We explore the LVE and LAOS rheology of carboxymethyl cellulose (CMC) in aqueous media, focusing on its gelling behaviour. We find that addition of HCl promotes gel formation and addition of NaOH suppresses it. The former effect is interpreted as being caused by a decrease of the charge density of the polymer, which facilitates interchain associations and the later effect can be assigned to solubilisation of cellulose backbone by NaOH. Our results along with a review of the literature allow us to establish the concentration regimes and associated properties of physical gels of carboxymethyl cellulose. At neutral pH, the storage modulus of NaCMC gels of varying molecular weight and DS at a given concentration does not vary by more than a factor 5.

Complexes of surfactants with oppositely charged polymers at surfaces and in bulk

Addition of surfactants to aqueous solutions of polyelectrolytes carrying an opposite charge causes the spontaneous formation of complexes in the bulk phase in certain concentration ranges. Under some conditions, compact monodisperse multichain complexes are obtained in the bulk. The size of these complexes depends on the mixing procedure and it can be varied in a controlled way from nanometers up to micrometers. The complexes exhibit microstructures analogous to those of the precipitates formed at higher concentrations. In other cases, however, the bulk complexes are large, soft and polydisperse. In most cases, the dispersions are only kinetically stable and exhibit pronounced non-equilibrium features. Association at air-water interfaces readily occurs, even at very small concentrations. When the surfactant concentration is small, the surface complexes are usually made of a surfactant monolayer to which the polymer binds and adsorbs in a flat-like configuration. However, under some conditions, thicker layers can be found, with bulk complexes sticking to the surface. The association at solid-water interfaces is more complex and depends on the specific interactions between surfactants, polymers and the surface. However, the behaviour can be understood if distinctions between hydrophilic surfaces and hydrophobic surfaces are made. Note that the behaviour at air-water interfaces is closer to that of hydrophobic than that of hydrophilic solid surfaces. The relation between bulk and surface complexation will be discussed in this review. The emphasis will be given to the results obtained by the teams of the EC-funded Marie Curie RTN "SOCON".

Adsorption behavior and activity of horseradish peroxidase onto polysaccharide-decorated particles

The adsorption behavior of horseradish peroxidase (HRP) onto hybrid particles of poly(methylmethacrylate) (PMMA) and carboxymethylcellulose (CMC) was investigated by means of spectrophotometry. Dispersions of PMMA/CMC particles were characterized by light scattering, zeta potential measurements and scanning electron microscopy before and after HRP adsorption. HRP adsorbed irreversibly onto PMMA/CMC particles; the adsorption isotherm showed an initial step and an adsorption plateau. The enzymatic activity of free HRP and immobilized HRP (plateau region) was monitored by means of spectrophotometry as a function of storing time. Upon adsorbing HRP there is little (up to 20%) or no reduction of enzymatic activity in comparison to that observed for free HRP in solution. After storing free HRP and HRP-covered PMMA/CMC particles for 18 days the level of enzymatic activity is kept. HRP-covered PMMA/CMC particles dispersions, which were dried and re-dispersed, retained 50% of their catalytic properties. These interesting findings were discussed in the light of a beneficial effect of a hydrated microenvironment for maintenance of enzyme conformation and activity.

Immobilization of Hexokinase onto Chitosan Decorated Particles

Chitosan (CH) decorated polystyrene (PS) particles were synthesized within complexes of CH, a polycation under acid conditions, and tiny amounts of sodium dodecylsulfate (SDS). Particle characterization was performed by means of dynamic light scattering, zeta potential measurements, and transmission electron microscopy. All dispersions were stable in the ionic strength of 2.0 mol L-1 NaCl during 2 months. The outstanding colloidal stability was attributed to the presence of a hydrated CH layer around the particles. CH decorated PS particles were attached to atomic force microscopy cantilevers and probed against Si wafers in water and in NaCl 0.01 mol/L. The mean thickness of CH layer amounted to 35 +/- 11 and 16 +/- 6 nm, when the medium was water and NaCl 0.01 mol/L, respectively. Adsorption isotherm of hexokinase (HK) onto PS/CH particles studied by means of spectrophotometry showed three regions: an initial step; adsorption plateau and multilayer formation. Enzymatic activity of free HK and immobilized HK was monitored by means of spectrophotometry as a function of storing time and reuse. After 3 days, storing HK free in solution dramatically lost its catalytic properties. On the contrary, HK-covered PS/CH particles retained enzymatic activity over 1 month. Moreover, HK-covered PS/CH particles could be reused in the determination of glucose two times consecutively, without losing activity. These interesting findings were discussed in light of the role of water in enzyme conformation.

Co-adsorption of carboxymethyl-cellulose and cationic surfactants at the air-water interface

We investigated the interaction between an anionic polyelectrolyte (carboxymethylcellulose) and cationic surfactants (DTAB, TTAB, and CTAB) at the air/water interface, using surface tension, ellipsometry, and Brewster angle microscopy techniques. At low surfactant concentration, a synergistic phenomenon is observed due to the co-adsorption of polyelectrolyte/surfactant complexes at the interface, which decreases the surface tension. When the surfactant critical aggregation concentration (cac) is reached, the adsorption saturates and the thickness of the adsorbed monolayer remains constant until another characteristic surfactant concentration, C0, is reached, at which all the polymer charges are bound to surfactant in bulk. Above C0, the absorbed monolayer becomes much thicker, suggesting adsorption of bulk aggregates, which have become more hydrophobic due to charge neutralization.

Sodium carboxymethylcellulose-CTAB interaction: a detailed thermodynamic study of polymer-surfactant interaction with opposite charges

Interaction between polymer and surfactant bearing opposite charges is much more complex from a physicochemical point of view as compared to interaction between ionic surfactant and nonionic polymer. Electrostatic and hydrophobic interactions interplay in the former, whereas the hydrophobic effect is the prevailing factor in the latter. We have studied the interaction between a water-soluble polyanion, sodium salt of carboxymethylcellulose (NaCMC), with a cationic amphiphile, CTAB, in aqueous medium. There were manifold discrepancies with the reported works in NaCMC-alkyltrimethylammonium bromide, which is assumed to be an effect of difference in degree of substitution, which in turn affects the charge density of the polymer chain. We have noticed that the bulk complexation and interfacial interaction driven by electrostatic forces operate side by side. Thereafter, there is a wrapping process by the polyanion to the polymer-induced smaller surfactant aggregates driven by increase in entropy of the solution as a result of expulsion of the counterions from the ionic atmosphere around the surfactant aggregate. Because of the electrostatic interaction, hydrophobicity of the polymer-surfactant complex increases, leading to coacervation, and again solubilization in the hydrophobic core of the self-aggregated structure provided by the added excess CTAB. The tensiometric, conductometric, microcalorimetric, and turbidimetric techniques have been applied to address these problems.

Ionically self-assembled carboxymethyl cellulose/surfactant complexes for antistatic paper coatings

We show that ionically self-assembled polyelectrolyte/surfactant complexes allow a facile route to tailor the electrical surface resistance of paper sheets for antistatic dissipative regime. We use anionic polyelectrolyte carboxymethyl cellulose (CMC) where cationic alkyltrimethylammonium chloride surfactants (C(n)TAC) with the alkyl chain lengths n=12, 14 or 16 methyl units are ionically complexed by precipitation from aqueous solutions. Such alkyl chains are sufficiently long to allow self-assembly in solid films after solvent evaporation. Short chain lengths, e.g., n=8, did not lead to precipitation. Small angle X-ray scattering indicates cylindrical self-assembly in bulk samples. Upon exposing bulk samples under humidity of 50% RH for 18 h, conductivity of ca. 10(-5) S/cm at room temperature is achieved based on AC-impedance analysis. Flexographic printing and spray coating were selected to conceptually test the feasibility as paper coatings and surface sheet resistances of ca. 10(9) Omega are reached. The results indicate that self-assembled polyelectrolyte/surfactant complexes can allow sufficient conductivity levels for antistatic paper coatings potentially due to protonic conductivity and suggest to develop processes and materials for realistic applications.

Thermodynamics of Self-Assembling of Hydrophobically Modified Cationic Polysaccharides and Their Mixtures with Oppositely Charged Surfactants in Aqueous Solution

Microcalorimetric techniques, combined with turbidity measurements, were used to study the thermodynamics of self-assembling of hydrophobically modified cationic polysaccharides and their mixtures with oppositely charged surfactants in aqueous solution. The studied polyelectrolytes were a series of polymers based on dextran having pendant N-(2-hydroxypropyl)-N,N-dimethyl-N-alkylammonium chloride groups randomly distributed along the polymer backbone. The parameters for their micellization process are evaluated from the results of the observed dilution enthalpy curves and compared with those of the related cationic surfactants (DTAC and CTAC). The microcalorimetric results for the mixed systems (polyelectrolytes with oppositely charged surfactants) are used along with turbidity measurements to characterize systematically the thermodynamics of their interaction. The phase behavior is described and the interaction enthalpies are derived from the differences between the observed enthalpy curves with and without polyelectrolyte. Therefore, we discuss in detail the effect of changing the alkyl chain length of polyelectrolyte pendant groups, the molecular weight of the dextran backbone, and the temperature of the measurements on the interactions between polyelectrolyte and surfactant.

Hybrid particles of polystyrene and carboxymethyl cellulose as substrates for copper ions

The synthesis of hybrid particles was carried out by emulsion polymerization of styrene in complexes formed by carboxymethyl cellulose (CMC), a polyanion, and a cationic surfactant, cetyltrimethylammonium bromide (CTAB). CMC chains with variable molecular weights and degrees of substitution were tested. The polymerization condition chosen was that corresponding to CMC chains fully saturated with CTAB and to the onset of pure surfactant micelle formation, namely, at the critical aggregation concentration. The hybrid particles were characterized by zeta potential and light scattering measurements. The period of colloidal stability in the ionic strength of 2.0 mol L(-)(1) NaCl was observed visually. Upon increasing the CMC chain length, the particle characteristics remained practically unchanged, but the colloid stability was increased. The increase in the CMC degree of substitution led to particles with more negative zeta potential values. The adsorption of copper ions (Cu(2+)) on the surface of hybrid particles could be described by the Langmuir model, as determined by potentiometric measurements. The increase in the mean zeta potential values and X-ray absorption near-edge spectra evidenced the immobilization of Cu(2+) ions on the hybrid particles.