Um experimento de análise em fluxo envolvendo reações enzimáticas e quimiluminescência

An experiment is proposed to introduce some fundamentals of flow analysis, chemiluminescence and kinetic monitoring of enzymatic reactions in undergraduate courses. Chemiluminescence detection is performed with a simple spectrophotometer equipped with a lab-made spiral flow cell constructed from a polyethylene tube. The hydrogen peroxide produced by the glucose oxidation in the presence of glucose oxidase is continuously monitored by the reaction with luminol in alkaline media in a flow injection system. The exercise allows also the discussion of important analytical features and the comparison with different optical methods of analysis.

Synthesis and NMR characterization of aliphatic-aromatic copolyesters by reaction of poly(ethylene terephthalate) post-consumer and poly(ethylene adipate)

An aliphatic-aromatic copolyester of poly(ethylene terephthalate), PET, and poly(ethylene adipate), PEA, PET-co-PEA, was synthesized by the high temperature melt reaction of post-consumer PET and PEA. As observed by NMR spectroscopy, the reaction yielded random copolyesters in a few minutes through ester-interchange reactions, even without added catalyst. The copolyesters obtained in the presence of a catalyst presented higher intrinsic viscosity than that obtained without the addition of catalyst, due to simultaneous polycondensation and ester-interchange reactions. The structure of the aliphatic-aromatic copolyesters obtained in different PET/PEA ratio is random as observed by NMR analysis.

Construção e avaliação de célula de fluxo para estudo da tensão interfacial dinâmica da interface fluxo líquido - sólido por despolarização da fluorescência

A simple low-cost flow cell was developed, built and optimized in order to observe dynamic interfacial tension of continuous flow systems. Distinct materials can be used in one of the cell walls in order to observe the intermolecular forces between the flowing liquid and the chemical constitution of the walls. The fluorescence depolarization was evaluated using Rhodamine B as fluorescent probe seeded in ethylene glycol. The effects of the positioning angles on the data acquired across the cell are reported. The reproducibility of the data was evaluated with a spectrometer assembled in-house and the relative standard deviation was below 3%.

Research on the suitability of organosolv semi-chemical triticale fibers as reinforcement for recycled hdpe composites

The main objective of this research was to study the feasibility of incorporating organosolv semi-chemical triticale fibers as the reinforcing element in recycled high density polyethylene (HDPE). In the first step, triticale fibers were characterized in terms of chemical composition and compared with other biomass species (wheat, rye, softwood, and hardwood). Then, organosolv semi-chemical triticale fibers were prepared by the ethanolamine process. These fibers were characterized in terms of its yield, kappa number, fiber length/diameter ratio, fines, and viscosity; the obtained results were compared with those of eucalypt kraft pulp. In the second step, the prepared fibers were examined as a reinforcing element for recycled HDPE composites. Coupled and non-coupled HDPE composites were prepared and tested for tensile properties. Results showed that with the addition of the coupling agent maleated polyethylene (MAPE), the tensile properties of composites were significantly improved, as compared to non-coupled samples and the plain matrix. Furthermore, the influence of MAPE on the interfacial shear strength (IFSS) was studied. The contributions of both fibers and matrix to the composite strength were also studied. This was possible by the use of a numerical iterative method based on the Bowyer-Bader and Kelly-Tyson equations

Kaukojäähdytysverkon rakennevaihtoehdot

Kaukojäähdytyksellä tarkoitetaan keskitetysti tuotetun jäähdytysenergian jakamista kiinteistöihin jakeluverkossa kiertävän kylmän veden välityksellä, eli kaukojäähdytys on ulkoistettu jäähdytysratkaisu. Jäähdytysenergiaa tarvitaan työtehon, viihtyisyyden ja sisäilman laadun parantamiseksi, sekä joidenkin prosessien tarpeisiin. Siinä missä perinteinen kiinteistökohtainen jäähdytysjärjestelmä tuottaa jäähdytysenergian sähköllä, käytetään kaukojäähdytyksessä jäähdytysenergian tuottamiseen sellaisia resursseja, jotka muuten jäisivät käyttämättä. Tästä syystä kaukojäähdytys vähentää merkittävästi hiilidioksidipäästöjä, jonka lisäksi kaukojäähdytys vähentää kylmäkoneissa käytettävien kylmäaineiden aiheuttamia kasvihuonekaasupäästöjä. Kaukolämpöverkkoa muistuttavan kaukojäähdytysverkon rakentaminen vaatii suuria investointeja. Nykyisin jakeluverkon rakenteena käytetään 2Mpuk- rakennetta, jonka todettiin olevan teknistaloudellisesti soveltuvin vaihtoehto Helsingin Energian kaukojäähdytysverkkoon. Myös PE 100 putkia voitaisiin käyttää PN 16 paineluokassa alle DN 300 kokoluokkaa vastaavissa johdoissa, ja PN 10 paineluokassa alle DN 400 johdoissa. Kaukolämpöverkon paineluokan valinta vaikuttaa oleellisesti investointikustannuksiin PE- putkilla ja joillekin alueille kannattanee rakentaa alemman paineluokan omaava erillisverkko PE- putkista. Happidiffuusion kautta PE- putkista pääsee jonkin verran happea verkkoon, mutta määrät ovat melko pieniä, eikä muitakaan teknisiä esteitä hyvin korroosiota kestävien PE- putkien käytölle ole. 2Mpuk- rakenteelle suurimman riskin aiheuttaa elementtien liitoskohdista teräsputken pinnalle pääsevä ulkopuolinen vesi. Koska kaukojäähdytysjohdot ovat lisäksi yleensä ympäristöä kylmempiä, kondensoivat ne vettä pinnallensa kaukolämpöjohdoista poiketen. Ulkopuolisen veden aiheuttamaa riskiä voitaisiin pienentää eristämällä liitoskohdat sähkömuhveilla. Verkoston rakentamiskustannuksia ja liikenteelle aiheutuvia haittoja voidaan vähentää ojattomia rakentamismenetelmiä, kuten suuntaporausta käyttämällä.

Avaliação da fotodegradação de poliolefinas através de exposição natural e artificial

Samples of polypropylene (PP) and low-density polyethylene (LDPE) were submitted to ultraviolet radiation, in the natural environment and also in the laboratory. Chemical modifications were quantified by the carbonyl index (CI), mechanical properties and melt flow index. The degradation in the laboratory was comparatively faster than in the environment for both types of polymers. The accelerating factor was determined for the various properties investigated. This parameter, however, showed a large variation with the degradation criteria and the type of polymer. The existence of a "universal accelerating factor", therefore, was not observed in the current study.

Desviaciones al modelo logarítmico-lineal en la solubilidad de ibuprofén y naproxén en mezclas cosolventes propilenoglicol-agua

The deviations observed in the solubility of ibuprofen (IBP) and naproxen (NAP) in propylene glycol (PG) + water (W) cosolvent mixtures with respect to the logarithmic-linear model proposed by Yalkowsky have been analyzed at 25.00 ± 0.05 ºC. Negative deviations were obtained in all cosolvent compositions for both drugs; they were greater for IBP. Another treatment, based on Gibbs free energy relationships, was also employed showing an apparent hydrophobicity chameleonic effect, because at low PG proportions NAP is more hydrophobic, whereas at high PG proportions IBP is more hydrophobic. The results are discussed in terms of solute-solvent and solvent-solvent interactions.

Influence of the temperature and type of salt on the phase equilibrium of peg 1500 + potassium phosphate and peg 1500 + sodium citrate aqueous two-phase systems

The present work analyzed the effect of the temperature and type of salt on the phase equilibrium of aqueous two-phase systems (ATPS) formed by poly (ethylene glycol) (PEG) 1500 + potassium phosphate, from (278.15 to 318.15) K, and PEG 1500 + sodium citrate, from (278.15 to 298.15) K. The rise of the temperature normally increased the slope of the tie line (STL). With respect to the influence of the type of salt, sodium citrate showed better capability to induce phase separation, when compared to potassium phosphate.

Síntese e caracterização de dispersões aquosas de poliuretanos à base de copolímeros em bloco de poli(glicol etilênico) e poli(glicol propilênico)

Non-polluting polyurethane aqueous dispersions, with 40% of solids content, were synthesized based on block copolymers of poly(ethylene glycol) and poly(propylene glycol) (PEG-b-PPG), with PEG hydrophilic segments content of 7 and 25%, poly(propylene glycol) (PPG), dimethylolpropionic acid (DMPA), isophorone diisocyanate (IPDI), and hydrazine. Different formulations were synthesized by varying the equivalent-grams ratios between isocyanate and hydroxyl groups (NCO/OH) and PPG and (PEG-b-PPG). The presence of high amounts of PEG in the formulations provoked the formation of gels. Average particle size and viscosity of the dispersions were determined. Mechanical properties and water absorption resistance of cast films were evaluated.

Desenvolvimento de sistemas líquido-cristalinos empregando silicone fluido de co-polímero glicol e poliéter funcional siloxano

For the construction of the phase diagrams, the method of the aqueous titration was used. There were prepared 5 ternary diagrams, varying the surfactant and the oil phase. The liquid-crystalline phases were identified by polarized light microscopy. The formulations prepared with silicon glycol copolymer, polyether functional siloxane (PFS) and water (S1) and with diisopropyl adipate, PFS and water (S4) presented liquid-crystalline phases with lamellar arrangement. Moreover, after 15 days in hot oven (37 ºC), the formulations presented hexagonal arrangement, evidencing the influence of the temperature in the organization of the system.

Estudo da resposta termicamente estimulada do compósito LDPE/CB por meio da técnica de corrente de despolarização termicamente estimulada (TSDC)

The thermally stimulated depolarization current (TSDC) in a range of temperature from 84 to 373 K, has been applied to study the depolarization current of polyethylene and polyethylene composites in form of film and filled with commercial or oxidative surface treatment carbon black. The diagrams of TSDC obtained show that the composite in which the carbon black had received oxidative surface treatment reducing on an average depolarization current intensity in a magnitude order if compared to the composite with commercial carbon black. Therefore in the area between α and β transitions the difference is accentuated by reaching a peak 55 times in a temperature of 240 K. The difference in results is explained in terms of molecular interactions neighboring of carbon black particles.

Avaliação do uso de poli(tereftalato de etileno) (PET) como matriz de imobilização de cinzas de incineradores

Industrial hazardous wastes must receive appropriate treatment to ensure a safe disposal to humans and environment. One of the techniques adopted for this purpose is the stabilization/solidification in polymer matrices. This paper evaluated the use of recycled polyethylene terephthalate as an incorporation matrix of incinerator ash. The polymer and the ash were submitted to an extrusion process in different percentages. The final product was evaluated through thermal and leaching tests and the leachate extracts constituents were determinated by atomic absorption spectrophotometry. The results showed a reduction in the release of substances up to 99% by mass for the conditions used.

Preparación de nanopartículas de plata en ausencia de polimeros estabilizantes

Silver nanoparticles (AgNPs) were prepared by means of the polyol method in the absence of stabilizing polymers. To accomplish this objective, AgNO3 was added to ethylene glycol in the presence of NaOH (1 mol.L-1), the suspension formed was irradiated with a microwave source for 60 seconds at a power of 465 watts. It was found that under these conditions AgNPs of sizes between 4-18 nm are formed. Also the results indicate that part of the ethylene glycol is oxidized to carbonyl compounds that reduce the Ag+. These organic compounds are adsorbed on the surfaces of AgNPs, forming a protective film that prevents their aggregation.

Quantificação de antimônio em garrafas de politereftalato de etileno (PET) brasileiras por fluorescência de raios-X e avaliação quimiométrica para verificar a presença de pet reciclado através do teor de ferro

Antimony is a common catalyst in the synthesis of polyethylene terephthalate used for food-grade bottles manufacturing. However, antimony residues in final products are transferred to juices, soft drinks or water. The literature reports mentions of toxicity associated to antimony. In this work, a green, fast and direct method to quantify antimony, sulfur, iron and copper, in PET bottles by X-ray fluorescence spectrometry is presented. 2.4 to 11 mg Sb kg-1 were found in 20 samples analyzed. The coupling of the multielemental technique to chemometric treatment provided also the possibility to classify PET samples between bottle-grade PET/recycled PET blends by Fe content.

Considerações sobre o preparo de amostras contendo micropoluentes estrogênicos

In this work, the materials used in the recovery of estrogens from aqueous matrices by filtration and solid phase extraction were evaluated. The results showed that glass-fiber filters allow a recovery and repeatability compatible with this type of analysis, whereas cellulose esters lead to significant losses of the analytes, mainly due to adsorption processes. On the other hand, the transferring of the sample to the extraction cartridges should be carried out with glass or Teflon tubing, since the adsorption observed with other polymeric materials (eg. silicone, Tygon, polyethylene and PVC) dramatically reduces the recovery and repeatability of the extraction process.