Marcia Rodrigues Pereira

Latexes based on ethyl methacrylate (EMA), acrylic acid (AA), crosslinked with 1,6-hexanediol propoxylate diacrylate (HPDA), were synthesized via emulsion polymerization, yielding dispersions with different acidic group contents and crosslinking densities. The latexes were thickened using various NaOH/AA molar ratios and the resultant dispersions were characterized by pH-metry, zeta potentiometry, and turbidimetry. The process of thickening by carboxyl neutralization was shown to be dependent on the neutralization effect on particle–particle interactions and particle solubilization. Turbidimetry, pH-metry, and zeta potential measurements showed that neutralization resulted in partial latex solubilization and viscometry indicated that, for a given latex, an optimum thickening was achieved for and specific NaOH/AA molar ratio, showing the existence of a relationship between thickening, particle–particle interactions, latex solubilization, and polyelectrolyte effect.

In this study carnauba straw powder was submitted to chemical treatments using alkali (NaOH) or hexane, in order to increase its hydrophilicity and to investigate its potential use for the development of a biodegradable composite. Biocomposites were prepared in solution, using carnauba straw powder and chitosan as matrix, with powder contents of 10 and 50 wt %. Both, straw powder and biocomposites, were characterized by chemical composition analysis, FTIR, TGA, DSC and SEM. According to the results, the chemical treatment using NaOH was efficient in removing the soluble components of the powder and cleaning its surface. DSC analyses demonstrated that the addition of high powder loadings does not reduce the thermal stability of the composite. The elastic modulus of the biocomposites obtained with 10 wt % of untreated carnauba powder remained unaltered, decreasing for a filler content of 50 wt %. The effect of NaOH chemical treatment was more evident for the composite with 50 wt % of powder

Textile industries produce a large quantity of effluents, which have high concentrations and variety of dyes. These substances, besides their poor aesthetic characteristics (when present in effluents), are extremely harmful to the environment. In this work, the sorption of the model dye Orange G was analyzed both in equilibrium and kinetic terms. Equilibrium experiments showed that Orange G sorption was well described by a Langmuir isotherm up to a point at which a Henry isotherm prevailed. This change in sorption mode was correlated to nonpolar interactions between dye and chitosan surface. An alternative kinetic description to the usual pseudo-order one was employed to describe the sorption of Orange G, following considerations based on ordinary collision rate theory. Both equilibrium and adsorption kinetics were heavily influenced by the presence of NaCl in the continuous phase.