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Search Results: 1 - 10 of 132484 matches for " Pires Alfredo T. Nunes "
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Influência do comon?mero e do método de polimeriza??o na cinética de libera??o de fenobarbitona a partir de hidrogéis
Barcellos, Ivonete O.;Katime, Issa A.;Soldi, Valdir;Pires, Alfredo T. Nunes;
Polímeros , 2000, DOI: 10.1590/S0104-14282000000200013
Abstract: the release of water-soluble drugs from initially hydrated hydrogels matrices generally involves the simultaneous water absorption and drug desorption through a swelling-controlled diffusion mechanism. the diffusional behaviour of phenobarbitone from a hydrogel formed by a 2-hydroxyethylmethacrylate (hema) and methyl monoitaconate (mmi) copolymer was reported. the drug release into water was performed by high pressure liquid cromatography and the results showed that the phenobarbitone release from the hydrogels studies, considering the diffusion coefficient values did not change with the temperature and the polymerization method. the activation energy values suggested a more favorable phenobarbitone release from the hydrogels p(hema-co-mmi) polymerized in mass and bulk solution.
Influência do comon mero e do método de polimeriza o na cinética de libera o de fenobarbitona a partir de hidrogéis
Barcellos Ivonete O.,Katime Issa A.,Soldi Valdir,Pires Alfredo T. Nunes
Polímeros , 2000,
Abstract: A libera o de drogas solúveis em água a partir de matrizes de hidrogéis hidratados, geralmente envolve simultaneamente a absor o de água e a libera o da droga via mecanismo de difus o controlada. Foi analisado o comportamento difusional da fenobarbitona no hidrogel do copolímero 2-hidroxietil metacrilato (HEMA) e monoitaconato de metila (MMI). A libera o da droga no meio aquoso foi acompanhada por cromatografia líquida de alta press o e os resultados mostraram que a libera o da fenobarbitona a partir dos hidrogéis estudados, considerando-se os valores dos coeficientes de difus o, n o variou com a temperatura e com o método de polimeriza o. Os valores de energia de ativa o sugerem um favorecimento na libera o da fenobarbitona a partir dos hidrogéis de p(HEMA-co-MMI) polimerizados em massa e em solu o.
Maleic Anhydride Grafting on EPDM: Qualitative and Quantitative Determination
Barra, Guilherme M.O.;Crespo, Janaina S.;Bertolino, José R.;Soldi, Valdir;Pires, Alfredo T. Nunes;
Journal of the Brazilian Chemical Society , 1999, DOI: 10.1590/S0103-50531999000100006
Abstract: several attempts have been made to compatibilize immiscible blends by introducing suitably-chosen polymer additives. this work studies the epdm elastomer, chemically modified with maleic anhydride (ma), through reaction in solution of epdm and ma, using dibenzoyl peroxide as an initiator. the best conditions for obtaining the maximum grafting were studied at different times and percentage weights of maleic anhydride. the evaluation of ma grafting onto epdm was determined with multiple internal reflectance infrared spectroscopy as discussed in detail.
Sociedades científicas brasileiras
Pires Alfredo Tibúrcio Nunes
Polímeros , 2000,
Protective effect of poly(4-Vinylpyridine) containing surface films to the corrosion of copper
Giacomelli, Cristiano;Giacomelli, Fernando Carlos;Schmidt, Vanessa;Santana, Adriana Lídia;Pires, Alfredo Tiburcio Nunes;Bertolino, José Roberto;Spinelli, Almir;
Journal of the Brazilian Chemical Society , 2005, DOI: 10.1590/S0103-50532005000100002
Abstract: we report here on the ability of poly(4-vinylpyridine) (p4vp) films to improve the copper corrosion properties in 0.1 mol l-1 h2so4. films formed by cu(p4vp)2(scn)2 macromecular-complex were electrochemically or spontaneously (by immersion) grown onto copper surfaces in 3% acetic acid, 0.1 mol l-1 kscn and p4vp containing solutions. imaging and electrochemical techniques were employed to characterize the film morphology and evaluate its effect on the copper corrosion, respectively. a substantial increase in corrosion resistance of copper samples spontaneously coated by p4vp films was found in comparison to the uncoated ones. the optimum conditions for spontaneous growth comprise a 3 - 4 h immersion period in a 0.1 mol l-1 p4vp containing solution. inhibition efficiencies (ie) of 94 - 98% were recorded by employing this methodology. for electrochemically grown p4vp films, the ie was 70 - 85%.
Interaction of poly(4-vinylpyridine) with copper surfaces: electrochemical, thermal and spectroscopic studies
Giacomelli, Cristiano;Giacomelli, Fernando Carlos;Santana, Adriana Lídia;Schmidt, Vanessa;Pires, Alfredo Tiburcio Nunes;Bertolino, José Roberto;Spinelli, Almir;
Journal of the Brazilian Chemical Society , 2004, DOI: 10.1590/S0103-50532004000600006
Abstract: the interaction of poly(4-vinylpyridine) (p4vp) and thiocyanate ions with copper in acid solutions was studied by cyclic voltammetry, thermogravimetry, elemental analysis and infrared spectroscopy. it is shown that at ca. -0.45 v/sce the electrogenerated cu(i) ions at the surface of a copper electrode induce a complexing reaction with p4vp and scn- both present in solution. the resulting electroactive polymer-complex grows onto the electrode surface as a film, and the metallic center is further oxidized to cu(ii) in a subsequent step at ca. -0.23 v/sce. according to thermogravimetric results, the polymer-complex is less thermally-stable than p4vp as evidenced by the lowering in the initial temperature of degradation from ca. 400 oc (p4vp) to ca. 200 oc (complex). the elemental analysis revealed a chemical composition of 2:1:2 for p4vp:cu:scn, and the infrared spectra indicated that the complex comprises a copper metallic center coordinated with nitrogen pyridinic rings (p4vp) and thiocyanate ions.
Characterization of thermoplastic starch/poly(lactic acid) blends obtained by extrusion and thermopressing
Müller, Carmen M. O.;Pires, Alfredo T. N.;Yamashita, Fabio;
Journal of the Brazilian Chemical Society , 2012, DOI: 10.1590/S0103-50532012000300008
Abstract: blends of poly(lactic acid) (pla)/thermoplastic starch (tps) were prepared by extrusion and thermopressing, with proportions of 0.1, 0.2 and 0.3 g of pla per g tps. thermoplastic starch was obtained from the extrusion of 0.30 g or 0.25 g of glycerol per g of starch. the mechanical properties and water vapor permeability were tested and water sorption isotherms were obtained. the morphological characteristics of the samples were observed through scanning electron microscopy (sem) and the thermal properties of the pure polymers and the blends by differential scanning calorimetry (dsc). the sem and dsc results indicated the immiscibility of the tps/pla blends and the presence of two phases. for blends with 20% and 30% of pla increases in the tensile strength and modulus were observed. the lowest water vapor permeability was observed for the blend with 30% of pla, which is related to the lowest diffusion coefficient value observed for this sample.
Moldes de ABS construídos pelo processo de modelagem por fus?o e deposi??o para inje??o de PP e PEBD
Foggiatto, José A.;Ahrens, Carlos H.;Salmoria, Gean V.;Pires, Alfredo T. N.;
Polímeros , 2004, DOI: 10.1590/S0104-14282004000500013
Abstract: rapid prototyping and rapid tooling are aimed at reducing the development time of products in the design phase by minimizing re-workings and, consequently, reducing the time to launch new products. in this work one of the technologies of rapid prototyping, called fused deposition modeling (fdm), was used in the construction of abs molds with the objective of investigating its application in the injection molding of thermoplastics. specimens of the molded parts were characterized with x-ray diffraction, shore d hardness and tensile tests. the results demonstrated the viability to manufacture small batches of ldpe and pp parts with mechanical properties similar to those molded parts in metallic molds.
Blendas de poliamida 6/elast?mero: propriedades e influência da adi??o de agente compatibilizante
Barra, Guilherme M. O.;Roeder, Jerusa;Soldi, Valdir;Pires, Alfredo T. N.;Agnelli, José A. M.;
Polímeros , 2003, DOI: 10.1590/S0104-14282003000200006
Abstract: this study describes the micro- and macroscopic properties of polyamide 6 (pa6) and ethylene /propylene/diene copolymer (epdm) blends, and the effects from small quantities of epdm or epm grafted with maleic anhydride in this polymer mixture. the components and polymer blends at different compositions were analyzed by differential scanning calorimeter (dsc) and infrared spectroscopy (ftir). the results suggest immiscible mixture in all ranges of the blend's compositions. scanning electron microscopy (sem) micrographs of the blends indicated that the size of rubber aggregates decreases as the functionalized elastomer (epdm-g-ma or epm-g-ma) is added to the pa6/epdm mixture, and the impact strength of the pa6 matrix increases significantly.
Prepara??o e caracteriza??o de membranas microporosas obtidas a partir de blendas de PVDF/PMMA.
Petrus, José Carlos C.;Menezes, Hilary C.;Pires., Alfredo T. N.;
Polímeros , 1998, DOI: 10.1590/S0104-14281998000100010
Abstract: abstract: microporous membranes were prepared from different blends of pvdf/pmma (polyvinylidene fluoride/polymethyl methacrylate) using the technique of phase inversion by immersion-coagulation in the presence of a non-solvent, dissolving the polymers in dmf (n'n'dimethylformamide). the membranes were characterized by scanning eletron microscopy, infrared internal reflection spectroscopy and differential scanning calorimetry, in addition to permeability and solute retention assays. different morphologies were obtained as the concentrations of the components in the blends were varied. an increase in the concentration of pmma reduced the degree of cristalinity of the pvdf and increased the overall porosity and thickness of the membranes, resulting in an important increase in the permeate flux rate and solute retention.
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