Caracterização de cálculos renais por análise térmica

Dez amostras de cálculos renais foram estudadas por Análise Elementar de CHN (EA), Espectroscopia de Absorção no Infravermelho (IV) e Difração de raios X pelo método de Pó (XRD). O comportamento térmico das amostras foi estudado por Termogravimetria/Termogravimetria Derivada (TG/DTG) e por Calorimetria Exploratória Diferencial (DSC). Os resultados de EA, Espectroscopia de Absorção IV e XRD mostraram a presença de estruvita [NH4Mg(PO4).6H2O], apatita, oxalato de cálcio monohidratado e oxalato de cálcio dihidratado. As curvas TG e DSC permitiram classificar as amostras em dois grupos diferentes: Grupo I mostrando comportamento térmico típico de estruvita e Grupo II apresentando um perfil termoanalítico característico de mistura de oxalatos.

Thermal behavior and decomposition kinetics of rifampicin polymorphs under isothermal and non-isothermal conditions

The thermal behavior of two polymorphic forms of rifampicin was studied by DSC and TG/DTG. The thermoanalytical results clearly showed the differences between the two crystalline forms. Polymorph I was the most thermally stable form, the DSC curve showed no fusion for this species and the thermal decomposition process occurred around 245 ºC. The DSC curve of polymorph II showed two consecutive events, an endothermic event (Tpeak = 193.9 ºC) and one exothermic event (Tpeak = 209.4 ºC), due to a melting process followed by recrystallization, which was attributed to the conversion of form II to form I. Isothermal and non-isothermal thermogravimetric methods were used to determine the kinetic parameters of the thermal decomposition process. For non-isothermal experiments, the activation energy (Ea) was derived from the plot of Log β vs 1/T, yielding values for polymorph form I and II of 154 and 123 kJ mol-1, respectively. In the isothermal experiments, the Ea was obtained from the plot of lnt vs 1/T at a constant conversion level. The mean values found for form I and form II were 137 and 144 kJ mol-1, respectively.

A comparative solid state (13)C NMR and thermal study of CO(2) capture by amidines PMDBD and DBN

The present work shows study of the CO(2) capture by amidines DBN and PMDBD using (13)C solid-state NMR and thermal techniques. The solid state (13)C NMR analyses demonstrate the formation of a single PMDBD-CO(2) product which was assigned to stable bicarbonate. In the case of DBN, it is shown that two DBN-CO(2) products are formed, which are suggested to be stable bicarbonate and unstable carbamate. The role of water in the DBN-CO(2) capture as well as the stability of the products to environmental moisture was also investigated. The results suggest that the carbamate formation is favored in dry DBN, but in the presence of water it decompose to form bicarbonate. Thermal analysis shows a good gravimetric CO(2) absorption of DBN. Release of CO(2) was found to be almost quantitative from the PMDBDH(+) bicarbonate about 110 degrees C.

CHEMICAL AND PHYSICO-CHEMICAL CHARACTERIZATION OF LIGNINS OBTAINED FROM ETHANOL-WATER FRACTIONATION OF BAGASSE

Organosolv lignins can replace petroleum chemicals such as phenol either partially or totally in various applications. Eight lignins, seven of which corresponded to the ethanol-water fractionation of bagasse and the other to a reference lignin (Alcell (R)) were analyzed with the aim to evaluate their chemical and physicochemical characteristics. The purity of the lignin fractions was determined by high pressure liquid chromatography (HPLC) and by ash content. Fourier Transform-Infrared Spectroscopy (FTIR) techniques and differential UV spectroscopy were applied to identify the chemical groups in the lignin samples. The molecular weight distribution was determined by size exclusion chromatography (HPSEC). Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques were used to determine the mass loss due to the high temperature treatment. The lignins studied showed the presence of p-hydroxyphenyl (H unit) and a greater proportion of guaiacyl (G unit) moieties, lower purity, similar or greater amount of phenolic hydroxyl groups, and higher degradation temperatures, than the Alcell (R) lignin.

Finite element analysis of concrete cracking at early age

The study of the early age concrete properties is becoming more important, as the thermal effects and the shrinkage, even in the first hours, could generate cracks, increasing the permeability of the structure and being able to induce problems of durability and functionality in the same ones. The detailed study of the stresses development during the construction process can be decisive to keep low the cracking levels. In this work a computational model, based on the finite element method, was implemented to simulate the early age concrete behavior and, specially, the evaluation of the cracking risk. The finite element analysis encloses the computational modeling of the following phenomena: chemical, thermal, moisture diffusion and mechanical which occur at the first days after the concrete cast. The developed software results were compared with experimental values found in the literature, demonstrating an excellent approach for all the implemented analysis.

Prospects in Lyophilization of Bovine Pericardium

Almost 30 years after the introduction of heart valve prostheses patients worldwide are benefiting from the implant of these devices. Among the various types of heart valves, the ones made of treated bovine pericardium have become a frequently used replacement of the heart`s native valve. Lyophilization, also known as freeze-drying, is an extremely useful technique for tissue storage for surgical applications. This article gives a brief overview on the current bovine pericardium lyophilization development, including the chemical modification to improve physical-chemical characteristics and the advanced technologies used to guarantee a high-quality product. It was shown that lyophilization process can be successfully applied as a method of bovine pericardium preservation and also as a technological tool to prepare new materials obtained by chemical modification of native tissues.

Thermal properties and release of Lippia sidoides essential oil from gum arabic/maltodextrin microparticles

Microencapsulation of Lippia sidoides essential oil was carried out by spray drying. Blends of maltodextrin and gum arabic were used as carrier. Spray dried microparticles were characterized using conventional (thermogravimetry, evolved gas analysis) and combined (thermogravimetry-mass spectrometry analysis) thermal analysis techniques in order to evaluate the abilities of carriers with different compositions in retaining and in releasing the core vs. dynamic heating. Thermal analysis was useful to evaluate the physico-chemical interactions between the core and carriers and to determine the protective effect of the carriers on the evaporation of essential oil.

Effect of neutralization and cross-linking on the thermal degradation of chitosan electrospun membranes

Thermal degradation of as electrospun chitosan membranes and samples subsequently treated with ethanol and cross-linked with glutaraldehyde (GA) have been studied by thermogravimetry (TG) coupled with an infrared spectrometer (FTIR). The influence of the electrospinning process and cross-linking in the electrospun chitosan thermal stability was evaluated. Up to three degradation steps were observed in the TG data, corresponding to water dehydration reaction at temperatures below 100 ºC, loss of side groups formed between the amine groups of chitosan and trifluoroacetic acid between 150 – 270 ºC and chitosan thermal degradation that starts around 250 ºC and goes up to 400 ºC. The Kissinger model was employed to evaluate the activation energies of the electrospun membranes during isothermal experiments and revealed that thermal degradation activation energy increases for the samples processed by electrospinning and subsequent neutralization and cross-linking treatments with respect to the neat chitosan powder.

Mechanical and thermal characterization of a structural polyurethane adhesive modified with thermally expandable particles

Thermally expandable particles (TEPs) are used in a wide variety of applications by industry mainly for weight reduction and appearance improvement for thermoplastics, inks, and coatings. In adhesive bonding, TEPs have been used for recycling purposes. However, TEPs might be used to modify structural adhesives for other new purposes, such as: to increase the joint strength by creating an adhesive functionally modified along the overlap of the joint by gradual heating and/or to heal the adhesive in case of damage. In this study, the behaviour of a structural polyurethane adhesive modified with TEPs was investigated as a preliminary study for further investigations on the potential of TEPs in adhesive joints. Tensile bulk tests were performed to get the tensile properties of the unmodified and TEPs-modified adhesive, while Double Cantilever Beam (DCB) test was performed in order to evaluate the resistance to mode I crack propagation of unmodified and TEPs-modified adhesive. In addition, in order to investigate the behaviour of the particles while encapsulated in adhesives, a thermal analysis was done. Scanning electron microscopy (SEM) was used to examine the fracture surface morphology of the specimens. The fracture toughness of the TEPs-modified adhesive was found to increase by addition of TEPs, while the adhesive tensile strength at yield decreased. The temperature where the particles show the maximum expansion varied with TEPs concentration, decreasing with increasing the TEPs content.

Thermal–mechanical behaviour of chitosan–cellulose derivative thermoreversible hydrogel films

CH, Chitosan; HPMC, (Hydroxypropyl)methyl cellulose; FT, Freeze-thaw; SC, Solvent casting; CH:HPMC (X:Y), pH Z, FT/SC, Chitosan and (hydroxypropyl)methyl cellulose hydrogel, at X and Y proportion (0-100), at Z pH (3.0-4.0) and prepared by freeze-thaw or solvent casting techniques; DSC, Differential scanning calorimetry; MDSC, Temperature modulated Differential scanning calorimetry; Tg, glass transition temperature; ΔH, enthalpy change; TGA, Thermogravimetric Analysis; TG, Thermogravimetry; DTG, Derivative or Differential thermogravimetry; σ, Tensile strength; ε, elongation at break; DMA, Dynamic mechanical analysis; X-Ray, X-radiation, FTIR-ATR, Attenuated total reflectance Fourier transform infrared spectroscopy; SEM, Scanning electron microscopy.

RNA-seq analysis of the Quercus suber root response to drought

Dissertação de mestrado em Plant Molecular Biology, Biotechnology and Bioentrepreneurship

Properties and thermal behavior of natural deep eutectic solvents

Natural deep eutectic solvents (NADES) have shown to be promising sustainable media for a wide range of applications. Nonetheless, very limited data is available on the properties of these solvents. A more comprehensive body of data on NADES is required for a deeper understanding of these solvents at molecular level, which will undoubtedly foster the development of new applications. NADES based on choline chloride, organic acids, amino acids and sugars were prepared, and their density, thermal behavior, conductivity and polarity were assessed, for different NADES compositions. The NADES studied can be stable up to 170 Â°C, depending on their composition. The thermal characterization revealed that all the NADES are glass formers and some, after water removal, exhibit crystallinity. The morphological characterization of the crystallizable materials was performed using polarized optical microscopy which also provided evidence of homogeneity/phase separation. The conductivity of the NADES was also assessed from 0 to 40 Â°C. The more polar, organic acid-based NADES presented the highest conductivities. The conductivity dependence on temperature was well described by the Vogelâ Fulcherâ Tammann equation for some of the NADES studied.

Ranking procedure based on mechanical, durability and thermal behavior of mortars with incorporation of phase change materials

Nowadays, considering the high variety of construction products, adequate material selection, based on their properties and function, becomes increasingly important. In this research, a ranking procedure developed by Czarnecki and Lukowski is applied in mortars with incorporation of phase change materials (PCM). The ranking procedure transforms experimental results of properties into one numerical value. The products can be classified according to their individual properties or even an optimized combination of different properties. The main purpose of this study was the ranking of mortars with incorporation of different contents of PCM based in different binders. Aerial lime, hydraulic lime, gypsum and cement were the binders studied. For each binder, three different mortars were developed. Reference mortars, mortars with incorporation of 40% of PCM and mortars with incorporation of 40% of PCM and 1% of fibers, were tested. Results show that the incorporation of PCM in mortars changes their global performance.

Beeswax organogels: Influence of gelator concentration and oil type in the gelation process

This work focused on how different types of oil phase, MCT (medium chain triglycerides) and LCT (long chain triglycerides), exert influence on the gelation process of beeswax and thus properties of the organogel produced thereof. Organogels were produced at different temperatures and qualitative phase diagrams were constructed to identify and classify the type of structure formed at various compositions. The microstructure of gelator crystals was studied by polarized light microscopy. Melting and crystallization were characterized by differential scanning calorimetry and rheology (flow and small amplitude oscillatory measurements) to understand organogels' behaviour under different mechanical and thermal conditions. FTIR analysis was employed for a further understanding of oil-gelator chemical interactions. Results showed that the increase of beeswax concentration led to higher values of storage and loss moduli (G, G) and complex modulus (G*) of organogels, which is associated to the strong network formed between the crystalline gelator structure and the oil phase. Crystallization occurred in two steps (well evidenced for higher concentrations of gelator) during temperature decreasing. Thermal analysis showed the occurrence of hysteresis between melting and crystallization. Small angle X-ray scattering (SAXS) analysis allowed a better understanding in terms of how crystal conformations were disposed for each type of organogel. The structuring process supported by medium or long-chain triglycerides oils was an important exploit to apprehend the impact of different carbon chain-size on the gelation process and on gels' properties.

Magnetization versus heat treatment in rapidly solidified NdFeB alloys

NdFeB melt-spun amorphous or partially amorphous alloys of four compositions were prepared. Their crystallization kinetics induced by thermal treatment was studied by differential scanning calorimetry and scanning and transmission electron microscopy. Scanning electron microscopy demonstrated that heterogeneous nucleation occurs preferentially at the ribbon surface which was in contact with the wheel. The explicit form of the kinetic equation that best describes the first stage of crystallization under high undercooling conditions was obtained for each alloy. From the crystallization results, the lower part of the experimental time-temperature-transformation curves was deduced for each alloy and extrapolated up to the high-temperature limit of their validity. Microstructural observations showed a typical size of the microcrystals obtained by heat treatment of ~100 nm. From the magnetic properties measured with a vibrating sample magnetometer, the same magnetic behavior of partially crystallized alloys is observed regardless of the temperature of annealing provided the same crystallization fraction, x, is achieved, at least for small values of x (typically ~10%).