860 resultados para ethylene-propylene terpolymer (EPDM)
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O objetivo deste trabalho foi avaliar a qualidade de couve-chinesa minimamente processada e tratada com cloreto de c��lcio (CaCl2), ��cido asc��rbico (vitamina C), ��cido etileno-diamino-tetrac��tico (EDTA) e mantida sob refrigera����o. Foram realizados os seguintes tratamentos: T1: testemunha (imers��o em ��gua contendo 50 mg L-1 clorin/5 minutos); T2: imers��o em solu����o contendo CaCl2 a 1%/5 minutos; T3: imers��o em solu����o contendo CaCl2 a 2%/5 minutos; T4: imers��o em solu����o contendo vitamina C a 1%/5 minutos; T5: imers��o em solu����o contendo Vitamina C a 2%/5 minutos; T6: imers��o em solu����o contendo EDTA a 1%/5 minutos; e T7: imers��o em solu����o contendo EDTA a 2%/5 minutos. Ap��s a realiza����o dos tratamentos a couve-chinesa foi centrifugada, embalada em bandejas de polietileno expandido, recoberta com policloreto de vinila (PVC) e armazenada em temperatura de 5 �� 1 ��C e umidade relativa (UR) de 90 �� 2% por 8 dias. As an��lises f��sico-qu��micas, qu��micas e sensoriais foram realizadas de dois em dois dias. A presen��a de Salmonella foi verificada somente ap��s a realiza����o dos tratamentos. A partir dos resultados obtidos procedeu-se �� an��lise de vari��ncia (ANAVA) e aplicou-se o teste de Tukey considerando-se um n��vel de signific��ncia p < 0,05. Houve influ��ncia significativa dos diferentes tratamentos nas caracter��sticas f��sico-qu��micas e qu��micas, como tamb��m nas avalia����es da apar��ncia geral e escurecimento. N��o foi detectada presen��a de Salmonella em nenhum dos tratamentos realizados. de acordo com os resultados obtidos conclui-se que a couve-chinesa minimamente processada nas condi����es experimentais utilizadas s�� estaria apta para o consumo at�� o quarto dia de armazenamento.
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Funda����o de Amparo �� Pesquisa do Estado de S��o Paulo (FAPESP)
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Nickel nanoparticles into silica-carbon matrix composites were prepared by using the polymeric precursor method. The effects of the polyester type and the time of pyrolysis on the mesoporosity and nickel particle dispersion into non-aqueous amorphous silica-carbon matrix were investigated by thermogravimetric analysis, adsorption/desorption isotherms and TEM. A well-dispersed metallic phase could be only obtained by using ethylene glycol. Weightier polyesters affected the pyrolysis process due to a combination of more amounts of carbonaceous residues and delaying of pyrolysis process. The post-pyrolyzed composites were successfully cleaned at 200 degrees C for I h in oxygen atmosphere leading to an increase in the surface area and without the occurrence of carbon combustion or nickel nanoparticles oxidation. The matrix composites presented predominantly mesoporous with pore size well defined in 38 angstrom, mainly when tetraethylene glycol was used as polymerizing agent. (C) 2007 Elsevier B.V. All rights reserved.
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O bloqueio de eventos dependentes da sinaliza����o do etileno pode afetar de maneira positiva ou negativa a qualidade de frutos tropicais ap��s o armazenamento refrigerado. Dessa forma, os objetivos do presente trabalho foram estudar o envolvimento do etileno no desenvolvimento de inj��rias de frio em tangor 'Murcott' e avaliar as respostas envolvidas no processo de resist��ncia ��s inj��rias. Os frutos foram expostos a 500nL L-1 de 1-metilciclopropeno (1-MCP) durante 12 horas ou imersos em solu����es contendo 2000nL L-1 de ethephon ou ��cido salic��lico durante cinco minutos antes de serem armazenados a 1��C, por 90 dias. Como controle, parte dos frutos foi armazenada a 1��C. O tratamento de frutos com ethephon ou ��cido salic��lico antecipou e intensificou as inj��rias de frio. Por outro lado, a inibi����o do etileno pelo 1-MCP retardou o surgimento dos sintomas e resultou em menor ��ndice de inj��rias e percentual de frutos podres ao final do armazenamento. A atividade da super��xido dismutase (SOD) foi intensificada aos 45 dias, contudo em menor intensidade nos frutos tratados com ��cido salic��lico. Nas avalia����es subsequentes, houve decr��scimo na atividade da SOD em todos os tratamentos, por��m aos 90 dias a intensidade manteve-se levemente superior �� observada nos primeiros 30 dias de armazenamento. Os teores de putrescina (Put) e espermina (Spm), no flavedo dos frutos, n��o sofreram significativa altera����o durante o armazenamento. em contrapartida, os teores de espermidina (Spd) foram mais afetados pelo estresse ocasionado pelo frio.
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Several routes and procedures have been used in these last years as an effort to achieve single-phase mesoscopic-size superconducting samples. In this paper, the effects of using citric acid (CA), tartaric acid (TA) and ethylenediaminetetraacetic acid (EDTA) as chelating agents and ethylene-glycol (EG) as polyhydroxy alcohol were studied in order to establish conditions to avoid the occurrence of BaCO(3) undesirable secondary phase in YBa(2)Cu(3)O(7-delta) (YBCO). Thermal evolution of intermediate compounds formed during the calcinations process by the use of different chelating agents was traced using thermogravimetric and spectroscopic methods. The obtained results indicated that the polymer breakdown of samples prepared using EDTA occurs at higher temperatures than others chelating agents and also reduces the occurrence of BaCO(3) secondary phase as studied by X-ray diffraction measurements. Furthermore, the magnetic response of the mesoscopic-size YBCO specimens obtained was verified showing that samples present different superconducting response.
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Films of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) and poly(propylene) (PP), PP/PHBV (4:1), blends were prepared by melt-pressing and investigated with respect to their microbial degradation in soil after 120 days. Biodegradation of the films was evaluated by Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, and X-ray diffraction. The biodegradation and/or bioerosion of the PP/PHBV blend was attributed to microbiological attack, with major changes occurring at the interphases of the homopolymers. The PHBV film was more strongly biodegraded in soil, decomposing completely in 30 days, while PP film presented changes in amorphous and interface phase, which affected the morphology.
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The effect of changes in the bulk dielectric constant on the DNA torsional properties was evaluated from plasmid circularization reactions. In these reactions, pUC18 previously linearized by EcoRI digestion was recircularized with T4 DNA ligase. The bulk dielectric constant of the reaction medium was decreased by the addition of different concentrations of neutral solutes: ethylene glycol, glycerol, sorbitol, and sucrose, or increased by the addition of glycine. The topoisomers generated by the ligase reaction were resolved by agarose-gel electrophoresis. The DNA twist energy parameter (K), which is an apparent torsional constant, was determined by linearization of the Gaussian topoisomers' distribution. It was observed that the twist energy parameter for the given solutes is almost linearly dependent on the bulk dielectric constant. In the reaction buffer, the twist energy parameter was determined to be 1100 +/- 100. By decreasing the dielectric constant to 74 with the addition of sorbitol, the value of the parameter reaches K = 900 +/- 100, whereas the addition of ethylene glycol leads to kappa = 400 +/- 50. Upon addition of glycine, which resulted in a dielectric constant equal to 91, the value of the twist energy parameter increased to K 1750 +/- 100. (c) 2007 Wiley Periodicals.
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We have investigated the effect of mixing spontaneously formed dispersions of the cationic vesicle-forming dioctadecyldimethylammonium chloride and bromide (DODAX, with X being anions Cl- (C) or Br- (B)) with solutions of the micelle-forming nonionic ethylene oxide surfactants penta-, hepta-, and octaethyleneglycol mono-n-dodecyl ether, C12En (n = 5, 7, and 8), and the zwitterionic 3-(N-hexadecyl-N,N-dimethylammonio)propane sulfonate (HPS). We used for this purpose differential scanning calorimetry (DSC), turbidity, and steady-state fluorescence spectroscopy to investigate the vesicle-micelle (V-M) transition yielded by adding C12En and HPS to 1.0 mM vesicle dispersions of DODAC and DODAB. The addition of these surfactants lowers the gel-to-liquid crystalline phase transition temperature (T-m) of DODAC and DODAB, and the transition becomes less cooperative, that is, the thermogram transition peak shifts to lower temperature and broadens to disappear when the V-M transition is complete, the vesicle bilayer becomes less organized, and the T., decreases, in agreement with measurements of the fluorescence quantum yield of trans-diphenylpolyene (t-DPO) fluorescence molecules incorporated in the vesicle bilayer. Turbidity data indicate that the V-M transition comes about in three stages: first surfactants are solubilized into the vesicle bilayer; after saturation, the vesicles are ruptured, and, finally, the vesicles are completely solubilized and only mixed micelles are formed. The critical points of bilayer saturation and vesicle solubilization were obtained from the turbidity and fluorescence curves, and are reported in this communication. The solubility of DODAX is stronger for C12En than it is for HPS, meaning that C12En solubilizes DODAX more efficiently than does HPS. The surfactant solubilization depends slightly on the counterion, and varies according to the sequence C12E5 > C12E7 > C12E8 > HPS.
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psi-Condensation of DNA fragments of about 4 kbp was induced by poly(ethylene glycol) (PEG), with degrees of polymerization ranging from 45 to 182, and univalent salt (NaCl). Using circular dichroism spectroscopy, we were able to accurately determine the critical amount of PEG needed to induce condensation, as a function of the NaCl concentration. A significant dependence on the PEG degree of polymerization was found. Phase boundaries determined for the multimolecular condensation were very similar to those observed previously for the monomolecular collapse, with two asymptotic regimes at low and high salt concentrations. We analyze our data using a theoretical model that properly takes into account both the polyelectrolyte nature of the DNA and the liquid crystallinity of the condensed phase. The model assumes that all PEG is excluded from the condensates and shows reentrant decondensation only at low salt. We also systematically study reentrant decondensation and find a very strong dependence on PEG molecular weight. At low PEG molecular weight, decondensation occurs at relatively low concentrations of PEG, and over a wide range of salt concentrations. This suggests that in the reentrant decondensation the flexible polymers used are not completely excluded from the condensed phase.
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Coordena����o de Aperfei��oamento de Pessoal de N��vel Superior (CAPES)
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Homogeneous catalysts prepared from rhodium trichloride in aqueous aromatic amines have been shown to reduce C-CI bonds under mild water gas shift conditions (T=100 degrees C, P-CO = 1.0 atm). In a 4-picoline/water solvent mixture, 1,2-dichloroethane is reduced to ethylene and ethane in yields compatible with the consumption of the reducing agent CO and with the formation of CO2. Variation of the catalyst solutions by using different substituted pyridines shows a pattern of catalytic activity parallel to that reported previously for H-2 production from the shift reaction, There is a moderate dependence of activity on the basicity of the aromatic amine, but a methyl group at the alpha-position exercises a strong negative steric effect. Long term studies show decrease of the activity with the time perhaps due to the build up of chloride in the medium. (C) 1999 Elsevier B.V. B.V. All rights reserved.
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Funda����o de Amparo �� Pesquisa do Estado de S��o Paulo (FAPESP)
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Nanoparticles of tin oxide, doped with Ce and Y, were prepared using the polymeric precursor method. The structural variations of the tin oxide nanoparticles were characterized by means of nitrogen physisorption, carbon dioxide chemisorption, X-ray diffraction, and X-ray photoelectron spectroscopy. The synthesized samples, undoped and doped with the rare earths, were used to promote the ethanol steam reforming reaction. The SnO2-based nanoparticles were shown to be active catalysts for the ethanol steam reforming. The surface properties, such as surface area, basicity/base strength distribution, and catalytic activity/selectivity, were influenced by the rare earth doping of SnO2 and also by the annealing temperatures. Doping led to chemical and micro-structural variations at the surface of the SnO2 particles. Changes in the catalytic properties of the samples, such as selectivity toward ethylene, may be ascribed to different dopings and annealing temperatures.
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Conselho Nacional de Desenvolvimento Cient��fico e Tecnol��gico (CNPq)
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Funda����o de Amparo �� Pesquisa do Estado de S��o Paulo (FAPESP)