Viviane G. Teixeira

Principais métodos de caracterização da porosidade de resinas à base de divinilbenzeno

This paper reviews the most important methods used to characterize the porosity of styrene-divinylbenzene resins. Methods such as adsorption of nitrogen for determination of surface area and mercury intrusion porosimetry for characterization of pore size distribution are related.

Viscometric study of chitosan solutions in acetic acid/sodium acetate and acetic acid/sodium chloride.

A viscometric study was carried out at 25°C to assess the physical-chemical behavior in solution and the mean viscometric molar mass (M¯v) of chitosan solutions with different deacetylation degrees, in two solvent mixtures: medium 1-acetic acid 0.3mol/L and sodium acetate 0.2mol/L; and medium 2-acetic acid 0.1mol/L and sodium chloride 0.2mol/L. Different equations were employed, by graphical extrapolation, to calculate the intrinsic viscosities [η] and the viscometric constants, to reveal the solvents quality: Huggins (H), Kraemer (K) and Schulz-Blaschke (SB). For single-point determination, the equations used were SB, Solomon-Ciuta (SC) and Deb-Chanterjee (DC), resulting in a faster form of analysis. The values of ̄M¯v were calculated by applying the equation of Mark-Houwink-Sakurada. The SB and SC equations were most suitable for single-point determination of [η] and ̄M¯v and the Schulz-Blachke constant (kSB), equal to 0.28, already utilized for various systems, can also be employed to analyze chitosan solutions under the conditions studied.

Synthesis and characterization of styrene–divinylbenzene loaded with di(2-ethylhexyl)phosphonic acid. I. Influence of diluent mixture on the porous structure of the copolymer

Styrene–divinylbenzene copolymers were synthesized in the presence of di(2-ethylhexyl)phosphonic acid (EHEHPA) to be applied in the separation of rare earths by extraction chromatography. The copolymers were prepared by suspension polymerization in the presence of pure EHEHPA or in a mixture with isooctane, heptane, or toluene. The composition of the diluent mixture employed in the synthesis was varied. The apparent density, fixed pore volume, and surface area of the copolymers were determined. The content of EHEHPA retained in the copolymer beads was also determined, and it was found to be independent of the porous structure of the copolymer matrix. That content was only dependent on the amount of EHEHPA present in the diluent mixture. The toluene/EHEHPA mixtures produced the copolymers with the best properties required for extraction chromatography supports.

Determination of accessible chloromethyl groups in chloromethylated styrene-divinylbenzene copolymers

This paper describes an evaluation of the method based on the quaternization of pyridine for determining the chloromethyl groups content in styrene-divinylbenzene copolymers with different kinds of porosity. Some modifications of the method described by Feinberg and Merrifield are proposed depending on the porous characteristic of the copolymer to be analyzed. The quaternization reaction was limited by the access of pyridine to chloromethyl groups that is governed by the swelling equilibrium of the copolymer in the reactant.

Resinas poliméricas para separação e pré-concentração de chumbo

This article gives an overview of polymer materials used for lead separation and preconcentration. Different kinds of polymer resins, commercial or not, are cited as well as the most used functional groups attached to polymer backbones. The synthesis of these resins and conditions of lead adsorption and elution are remarked. The influence of the porous structure of the polymer on the resines performance is described as well as the use of spacer arms.

Principais rotas de síntese de resinas complexantes de mercúrio

The recovery of mercury and its compounds by using chelating resins produced by modification of polymer supports has been studied by many researchers. There are many combinations of supports and functional groups for producing chelating resins that are appropriate for mercury complexation. This paper presents an overview of the main functional groups applied for mercury complexation and the routes used for immobilization of these groups in polymer supports. Also discussed are the problems involved in the synthesis of an efficient chelating resin, produced through a non-polluting route, which are appropriate for companies employing mercury in their processes.

Síntese e caracterização de copolímeros de estireno e divinilbenzeno clorometilados

Cloromethylation of styrene-divinylbenzene copolymer (S-DVB) in presence of hydrogen chloride, formaldehyde and zinc chloride was studied in aqueous and organic media. S-DVB was first synthesized by suspension polymerization and its porosity was characterized. In aqueous medium, S-DVB was chloromethylated by using a mixture of hydrogen chloride, aqueous formaldehyde solution (formalin 37%) and aqueous zinc chloride solution as catalyst. In organic medium (1,2-dichloroethane), a mixture of hydrogen chloride, paraformaldehyde and solid zinc chloride was employed. The presence of chloromethyl groups in the copolymer was investigated by infrared spectroscopy analysis and titration of chloride ions, after a quaternization reaction between the chloromethylated copolymer and pyridine. The reaction in aqueous medium seems to be very difficult to occur even in the presence of solid zinc chloride (catalyst) and concentrated hydrochloric acid as reaction medium. Organic medium offers a better condition for aromatic eletrophilic substitution, where the reaction occurred in a more satisfactory way. The influence of reaction parameters was studied. Temperature and copolymer/catalyst ratio were the main responsible factors for the attained chloromethylation degree.

Copolímeros de estireno-divinilbenzeno impregnados com agentes complexantes organofosforados para separação de terras raras

RESUMO: Copolimeros de estireno-divinilbenzeno para aplicacao em cromatografia de extracao foram sintetizados em presenca de agentes complexantes seletivos para terras raras, o fosfato monoacido de bis(2-etil-hexila), DEHPA e o 2-etil-hexil fosfonato monoacido de 2-etil-hexila, EHEHPA. Os copolimeros foram preparados atraves de polimerizacao em suspensao utilizando como diluentes os agentes complexantes puros ou combinados com o solvente tolueno (TOL). A influencia das condicoes de sintese, tais como: a razao agente complexante/TOL; o grau de diluicao dos monomeros e o teor de divinilbenzeno, na estrutura porosa dos copolimeros foi investigada atraves de suas caracteristicas fisicas tais como densidade aparente, volume de poros fixos, area especifica e atraves de microscopia otica e eletronica de varredura. Os copolimeros foram avaliados em relacao ao processo de separacao de terras raras. Assim foram determinadas a capacidade total e a cinetica de complexacao em relacao ao ion gadolinio. O teor de agente complexante impregnado em cada suporte foi funcao da quantidade do agente complexante nas misturas. Foi otimizada a quantidade maxima do agente complexante que pode ser utilizada na sintese, de modo a obter suportes com alta capacidade de complexacao, sem o comprometimento de sua resistencia mecânica. A capacidade total de complexacao variou com a quantidade de agente complexante impregnado no suporte e a cinetica de complexacao variou principalmente com o diâmetro medio de poros, pois este determina a velocidade de difusao dos ions no suporte.