M. R. Pereira

Equilibrium and kinetic analysis of methyl orange sorption on chitosan spheres.

Chitosan can be used as adsorbent in the treatment of effluents from the textile industry, especially for negatively charged dyes, due to its cationic polyelectrolyte nature. In this work, the sorption of a model dye, methyl orange, on chitosan hydrobeads is analyzed in terms of equilibrium and kinetic approaches. Equilibrium studies showed that dye adsorption had a mixed Freundlich-Langmuir behavior that had its Langmuir character increased as the pH was increased. In terms of adsorption kinetics, it was found to be of nth-pseudo-order, with fractional n increasing from approximately 2 to approximately 2.5 as pH and initial dye concentration in the continuous phase were increased. The increase in the apparent pseudo-order was related to changes in mathematical approximation for the solution of the sorption rate equation, which were the result of the decrease in the ratio (number of active sites for adsorption)/(number of adsorbate molecules).

Polyelectrolytes in solution and the stabilization of colloids

Polyelectrolytes are very versatile macromolecular materials that have found more and more applications in several technologies. In this article applications related to their use as (de)stabilizers for colloids are reviewed. Additionally, some theories that deal with colloid stabilization are described. Finally, the rheology of the disperser phase as well as the relationship between the rheology of the whole colloidal system and polyelectrolyte stabilization are discussed.

Evaluating the possible anticoagulant and antioxidant effects of sulfated polysaccharides from the tropical green alga Caulerpa cupressoides var. flabellata

Seaweeds are a source of several biopolymers widely used in cosmetics, food, and pharmaceuticals. Among them are sulfated polysaccharides, which have several biological/pharmacological activities, such as antioxidant and anticoagulant activities. In the present study, four sulfated polysaccharides, denominated CCB-F0.3, CCB-F0.5, CCB-F1.0, and CCB-F2.0, were obtained from the chlorophyte Caulerpa cupressoides var. flabellata through proteolytic digestion, followed by acetone fractionation and molecular sieving in Sephadex G-100. Chemical analyses showed that CCB-F0.5 had the highest sulfate/sugar ratio (0.73), whereas CCB-F1.0 exhibited the lowest ratio (0.23). Polysaccharides from C. cupressoides displayed a heterogeneous constitution of monosaccharides, with galactose as the main sugar unit (except for CCB-F2.0). The presence of sulfated polysaccharides was confirmed by electrophoretic and infrared analyses. Sulfated polysaccharides showed no activity in superoxide and hydroxyl radical scavenging; however, they did demonstrate total antioxidant capacity and ferrous chelating activity. Caulerpa polysaccharides also exhibited anticoagulant activity in the intrinsic (activated partial thromboplastin time (aPTT) test) and extrinsic pathway (prothrombin time (PT) test). In the aPTT test, all polysaccharides displayed considerable dose-dependent activity. A significant result was the aPTT activity of the polysaccharides CCB-F0.3 and CCB-F0.5, which was similar to that of Clexane®, a commercial low molecular weight heparin. In addition, CCB-F0.3 and CCB-F0.5 showed PT activity. Sulfated polysaccharides from C. cupressoides are therefore promising antioxidant agents in preventing the formation of reactive oxygen species and for their possible use in anticoagulant therapy.

Chitosan membranes modified by contact with poly(acrylic acid)

In this work chitosan membranes modified by contact with poly(acrylic acid) (PAA) aqueous solution at two different temperatures (25 degrees C and 60 degrees C) were obtained. The pure chitosan (CS) membranes, as well as those treated with PAA (CSPAA_25 and CSPAA_60) were characterized by FTIR-ATR, water sorption capacity, thermal analysis (TG/DTG), and scanning electron microscopy (SEM). In addition, in vitro permeation experiments were carried out using metronidazol and sodium sulfamerazine aqueous solutions at 0.1% and 0.2% as model drugs. FTIR-ATR results showed the presence of absorption bands of NH3+ and COO(-) indicating the formation of a polyelectrolyte complex between chitosan and poly(acrylic acid). The results also indicated that PAA penetrates deeper into the membrane at higher temperature (60 degrees C), forming a thicker complex layer. Polyelectrolyte complex formation as well as the influence of treatment temperature was confirmed by lower hydrophilicity, higher thermal stability, and lower permeability of the treated membranes. The results show that the methodology used is a simple and very efficient way to drastically change some membrane properties, especially their permeability.

Viscometric monitoring of poly(ethylene oxide) degradation

The degradation of poly(ethylene oxide) was carried out using viscometry as a way of quantifying it in situ. The method was adequate to follow the kinetics of degradation, the main advantadge being that, for high polymer molecular weights and low concentration of persulfate, the kinetics are simplified by reduction to a simple linear function for any order. Deviations from these functions were corretated to disentanglement kinetics being important in the viscometric monitoring and/or higher occurrence of end groups for long degradation times.

Effect of irradiation times on the polymerization depth of contemporary fissure sealants with different opacities

The aim of this study was to evaluate the depth of curing of 10 contemporary blue light-activated dental flowable materials at several opacities, influenced by different irradiation times using FT-IR spectroscopy. Fifty-five specimens (n = 5) with a 5-mm diameter and 1-mm thickness of translucent (Opallis Flow T), yellowed (Master Flow A2; Opallis Flow A2; Natural Flow A2; Fluroshield Yellowed), and opaque materials (Master Flow OA2; Natural Flow O; Opallis Flow OA3.5; Opallis Flow OP; Fluroshield White) were obtained at six curing times (10s, 20s, 30s, 40s, 50s, and 60s) using a high-intensity LED (Coltolux, Coltène/Whaledent). The degree of conversion (DC) (%) was obtained using the Nexus 470 FTIR Spectrometer (Nicolet Instruments, USA). The FTIR-ATR spectra for uncured and cured samples were analyzed using a ZnSe crystal. The top and bottom surfaces of the cured specimens were analyzed to obtain the depth of curing. Two-way ANOVA was used to analyze the data. The highest curing depth was obtained by Natural Flow OA2, while the lowest was shown by Master Flow OA2. The shortest curing time generated similar depths of cure in comparison with the most extensive for Opallis Flow A2 and Fluroshield Yellowed. Therefore, depth of curing, influenced by the irradiation time, was dependent on the materials. Using the Natural Flow OA2 opaque sealant and the 10-s curing time for Opallis Flow A2 and Fluroshield Yellowed may represent alternative approaches to sealing tooth fissures.

Polyelectrolyte effect and settling of alumina dispersions

Abstract Sedimentation experiments were carried out in columns in which particle–particle interactions were minimized. Particle concentration profiles were generated using turbidity measurements at different times and heights of the column. This was done using the relationship between turbidity, time, and a dimensionless diameter, specified using a simple Stokes relationship. The method was proved to be sufficient to characterize the occurrence of destabilization in these dispersions which, in this paper, was correlated with work already published in this field, using different methods.

Preparation and characterization of PAni-PMMA dispersions

Blends of polyaniline (PAni) and poly(methyl methacrylate) (PMMA) have been produced using core‐shell particle synthesis, which is advantageous because it allows changing surface‐related properties of PMMA with relatively small amounts of PAni and without the use of organic solvents. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements indicated that the deposition of polyaniline seems to alter the regular shape of the primary acrylic latex particles. The coverage of PMMA particles by PAni was confirmed by FTIR measurements, where distinct data were obtained from the transmission and diffuse reflectance modes, since the latter is surface sensitive. The zeta potential, which is also a surface‐related property, increased with the contents of PAni, as the shells probably became protonated with PAni in the emeraldine salt form. Coverage with PAni did not affect the thermal bulk properties of the PMMA shells.

Preparation of Acrylic Latexes with Dispersed Magnetite Nanoparticles

Latexes based on ethyl methacrylate and acrylic acid with dispersed magnetite particles were obtained using the technique of miniemulsion polymerization. The polymerizations were carried out (using AIBN as the initiator) after the dispersion of magnetite particles hydrophobized with oleic acid in the acrylic monomers and miniemulsion formation with sodium dodecyl sulfate. Latex nonvolatile content, as well as thermogravimetric behavior of dry solid particles were a function of oleic acid content. Atomic force microscopy analysis of films formed with these latexes revealed the occurrence of ordered patterns on their surfaces.

Preparation, Characterization and Luminescence Study of Chitosan Membrane and Powder Forms with Eu3 + and Tb3 +

Chitosan membranes with trivalent lanthanide ion Eu3 + were prepared at a ratio of 3:1 w/w (chitosan:lanthanide). There was no membrane formation at a ratio of 1:1 w/w (chitosan: Eu3 + or Tb3 +); in this case a white solid powder was obtained. Both chitosan compounds were characterized by elemental analysis (CHN), thermal analysis (TG/DTG), scanning electron microscopy (SEM) and luminescence spectroscopy. CHN analysis was performed only for chitosan compounds in powder form, suggesting that these compounds have the general formula QUILn.6H2O, where QUI = Chitosan and Ln = Eu3 + or Tb3 +. The results of TG/DTG curves for chitosan membranes with Eu3 + ion indicate that the introduction of this metal into the chitosan structure causes gradual degradation in residual carbons, showing lower weight loss in the Eu3 + membranes compared to pure chitosan membrane. Analysis of luminescence demonstrated that chitosan membranes with Eu3 + ion exhibit emission in the visible region, showing emission bands from chitosan and Eu3 + moieties. For chitosan with Eu3 + and Tb3 + ions compounds, in powder form, the analysis of luminescence suggested that chitosan is not transferring energy to the lanthanide ion; however, the chemical region where the lanthanide ion is found breaks the selection rules and favors the emission of these ions.