Repositório Institucional da Universidade de Aveiro
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Synthesis and Characterization of Hybrid Mesoporous Materials Prepared with Triblock-Copolymer and Bridged Silsesquioxane
No full textRetama sphaerocarpa: An unexploited and rich source of alkaloids, unsaturated fatty acids and other valuable phytochemicals
No full textThe chemical composition of the lipophilic extracts of the stems and grains of the shrub Retama sphaerocarpa was investigated by gas chromatography-mass spectrometry for the first time. Fatty acids is the major family of compounds in both morphological parts, representing between 37.1 and 85.1% of the total compounds detected, followed by sterols in stems and monoglycerides in grains. Considerable amounts of the alkaloids retamine (9.6 g kg(-1). of dry material) and cytisine (0.6 g kg(-1) of dry material) were also found in stems and grains, respectively. Before alkaline hydrolysis octadec-9-enoic (0.7-2.4 g kg(-1) of dry material), octadeca-9,12-dienoic (1.5-2.9 g kg(-1) of dry material) and hexadecanoic (1.1-2.0 g kg(-1) of dry material) acids are the most abundant lipophilic components in both morphological parts. After alkaline hydrolysis the contents of octade-9-enoic, octadeca-9,12-dienoic and octadeca-9,12,15-trienoic acids detected increased considerably ranging from 1.9 to 22.4, 3.6 to 40.1 and 0 to 8.6 g kg(-1) of dry material, respectively. Smaller amounts of long-chain aliphatic alcohols, alpha-tocopherol and beta-amyrin were also found. These data indicates that R. sphaerocarpa stems and grains are a potential source of valuable phytochemicals, with recognized nutritional and phytopharmaceutical applications. (C) 2015 Elsevier B.V. All rights reserved
Wood waste incorporation for lightweight porcelain stoneware tiles with tailored thermal conductivity
No full textThe increasing demand for building materials exerts tremendous pressure on the Earth's natural resources, as many raw materials are reaching critical and distressing levels. As a result new materials that can, totally or partially, substitute conventional raw materials have been the focus of intense research and are eagerly pursued. Waste materials emerge as ideal candidates for partial substitution of ceramic raw materials, due to their large scale production. Despite their high annual production rate wood wastes have seldom be used in building materials, so their valorisation in the construction sector would be highly advantageous from an environmental and economic point of view. This work reports the incorporation of wood wastes (sawdust) as a pore forming agent into ceramic tiles for the production of lightweight bi-layered ceramic tiles with tailored thermal conductivity. To the best of our knowledge this is the first investigation concerning the incorporation of wood wastes in this type of material. Optical micrographs of the sintered discs did not reveal the presence of a black core, indicating that sawdust was totally burn out even when industrial fast-firing cycles were applied. Moreover its decomposition does not induce defects in the ceramic bodies. The results demonstrate that sawdust incorporation promotes a threefold decrease in the thermal conductivity of the ceramic tile, and reduces product weight (up to 7.5%), while maintaining suitable mechanical resistance in comparison to commercial stoneware tiles. Sawdust can be successfully incorporated into stoneware ceramic tiles ensuring environmental, technical and economic advantages: waste valorisation by sawdust reuse (environmental advantage); density reduction of the product which decreases the tiles transportation and distribution costs (economic advantage); restrain energy loss (technical advantage). The new and exciting features provided by sawdust incorporation may widen the range of applications of this common product while simultaneously contributing towards sustainable construction. (C) 2014 Elsevier Ltd. All rights reserved
Characterization and antimicrobial properties of food packaging methylcellulose films containing stem extract of Ginja cherry
No full textBACKGROUND: Food contamination and spoilage is a problem causing growing concern. To avoid it, the use of food packaging with appropriate characteristics is essential; ideally, the packaging should protect food from external contamination and exhibit antibacterial properties. With this aim, methylcellulose (MC) films containing natural extracts from the stems of Ginja cherry, an agricultural by-product, were developed and characterized. RESULTS: The antibacterial activity of films was screened by the disc diffusion method and quantified using the viable cell count assay. The films inhibited the growth of both Gram-positive and Gram-negative strains (Listeria innocua, methicillin-sensitive Staphylococcus aureus, methicillin-resistant S. aureus, Salmonella Enteritidis, Escherichia coli). For the films with lower extract content, effectiveness against the microorganisms depended on the inoculum concentration. Scanning electron microscope images of the films showed that those containing the extracts had a smooth and continuous structure. UV-visible spectroscopy showed that these materials do not transmit light in the UV. CONCLUSION: This study shows that MC films containing agricultural by-products, in this case Ginja cherry stem extract, could be used to prevent food contamination by relevant bacterial strains and degradation by UV light. Using such materials in food packaging, the shelf life of food products could be extended while utilizing an otherwise wasted by-product. (C) 2013 Society of Chemical Industr
Systematic Study of the Thermophysical Properties of Imidazolium-Based Ionic Liquids with Cyano-Functionalized Anions
No full textIn the past few years, ionic liquids (ILs) with cyano-functionalized anions have shown to be improved candidates for electrochemical and separation applications. Nevertheless, only scattered data exist hitherto and a broad analysis of their structure-property relationship has yet to be attempted. Therefore, in this work, a systematic study of the densities, viscosities and refractive indices of imidazolium-based ILs with cyano-functionalized anions was carried out at 0.1 MPa within a broad temperature range (from 278 to 363 K). The ILs under study are based on 1-alkyl-3-methylimidazolium cations (alkyl = ethyl, butyl and hexyl) combined with the [SCN](-), [N(CN)(2)](-), [C(CN)(3)](-) anions. The selected matrix of cation/anion combinations allows us to provide a detailed and comprehensive investigation of the influence of the -CN group through an analysis of the thermophysical properties of the related ILs. The results show that, regardless of the cation, the densities decrease with an increase in the number of cyano groups or anion molecular weight. Moreover, for a fixed cation and temperature, the refractive index of the ILs decreases according to the rank [SCN](-) > [N(CN)(2)](-) approximate to [C(CN)(3)](-) > [B(CN)(4)](-). On the other hand, no clear trend was observed for the viscosity of ILs and the respective number of -CN groups. The viscosity dependence on the cyano-functionalized anions decreases in the order: [SCN](-) > [B(CN)(4)](-) > [N(CN)(2)](-) > [C(CN)(3)](-). The isobaric thermal expansion coefficient, the derived molar refraction, the free volume, and the viscosity energy barrier of all compounds were estimated from the experimental data and are presented and discussed. Finally, group contribution models were applied, and new group contribution parameters are presented, extending these methods to the prediction of the ILs properties
Artifact level produced by different femoral head prostheses in CT imaging: diamond coated silicon nitride as total hip replacement material
No full textCommercial femoral head prostheses (cobalt-chromium alloy, yttria partially stabilized zirconia (Y-PSZ) and alumina) and new silicon nitride ceramic ones (nanocrystalline diamond coated and uncoated) were compared in terms of artifact level production by computed tomography (CT). Pelvis examination by CT allows the correct diagnosis of some pathologies (e.g. prostate and colon cancer) and the evaluation of the prosthesis-bone interface in post-operative joint surgery. Artifact quantification is rarely seen in literature despite having a great potential to grade biomaterials according to their imaging properties. Materials' characteristics (density and effective atomic number), size and geometry of the prostheses can cause more or less artifact. A quantification procedure based on the calculation of four statistical parameters for the Hounsfield pixel values (mean, standard deviation, mean squared error and worst case error) is presented. CT sequential and helical scanning modes were performed. Results prove the artifact reproducibility and indicate that the cobalt-chromium and Y-PSZ are the most artifact-inducing materials, while alumina and silicon nitride (diamond coated and uncoated) ceramic ones present a low level of artifact. Considering the excellent biocompatibility and biotribological behaviour reported in earlier works, combined with the high medical imaging quality here assessed, diamond coated silicon nitride ceramics are arising as new materials for joint replacement
Fast synthesis of rare-earth (Pr3+, Sm3+, Eu3+ and Gd3+) doped bismuth ferrite powders with enhanced magnetic properties
No full textRare-earth (Pr3+, Sm3+, Eu3+ and Gd3+) doped bismuth ferrite powders were synthesized for the first time by solution combustion method, which is a fast soft chemistry route for obtaining oxide powders. The materials were investigated by X-ray diffraction, Raman spectroscopy, as well as scanning and transmission electron microscopy. A distortion from rhombohedral R3c symmetry, specific to pure bismuth ferrite, to orthorhombic symmetry was observed for all doped samples. The SEM analysis of pure and doped bismuth ferrite powders showed the formation of sintered grains, with faceted cuboids-shaped particles with different size and lower average dimension in the case of doped samples. Magnetic properties were analyzed using SQUID magnetometry, M-H hysteresis loops being measured at 10 K and 300 K. All studied pure and doped bismuth ferrite samples presented high susceptibility values for high magnetic fields indicating strong antiferromagnetic interactions, whereas the behavior at low magnetic field demonstrates the existence of ferromagnetic coupling. Compared to BiFeO3, Bi0.9RE0.1FeO3 (RE = Pr, Sm, Eu and Gd) powders exhibit higher susceptibility, remanence and coercivity values, Bi0.9Eu0.1FeO3 sample displaying the highest remanence and coercivity at room temperature. (C) 2014 Elsevier B.V. All rights reserved
Conformational dynamics and aggregation behavior of piezoelectric diphenylalanine peptides in an external electric field
No full textAromatic peptides including diphenylalanine (FF) have the capacity to self-assemble into ordered, biocompatible nanostructures with piezoelectric properties relevant to a variety of biomedical applications. Electric fields are commonly applied to align FF nanotubes, yet little is known about the effect of the electric field on the assembly process. Using all-atom molecular dynamics with explicit water molecules, we examine the response of FF monomers to the application of a constant external electric field over a range of intensities. We probe the aggregation mechanism of FF peptides, and find that the presence of even relatively weak fields can accelerate ordered aggregation, primarily by facilitating the alignment of individual molecular dipole moments. This is modulated by the conformational response of individual FF peptides (e.g., backbone stretching) and by the cooperative alignment of neighboring FF and water molecules. These observations may facilitate future studies on the controlled formation of nanostructured aggregates of piezoelectric peptides and the understanding of their electro-mechanical properties. (C) 2014 Elsevier B.V. All rights reserved
Clay-Graphene Nanoplatelets Functional Conducting Composites
No full textAn approach to functionalize graphene-based materials has been developed by assembling graphene nanoplatelets (GNP) with clay minerals. Under convenient sonomechanical treatment, clay-GNP mixtures may produce very stable water dispersions in particular using sepiolite fibrous clay. While in the absence of clay a rapid decantation of GNP in water is observed, in the presence of sepiolite the resulting dispersions remain stable during months without syneresis effects. Rigid but flexible self-supported films are easily obtained by filtering of these dispersions. As the electrical percolation threshold corresponds to sepiolite/GNP composites of 0.5:1 in weight, doping these systems with multiwalled carbon nanotubes (MWCNTs) significantly enhances their electrical conductivity. The particular microporosity of the sepiolite component allows interactions with molecules, such as organic dyes, as well as polymers, such as biopolymers, opening the way to functional materials for advanced applications due to their inherent conductivity afforded by the GNP and MWCNTs carbonaceous components. In fact, using very small amount of MWCNT together with GNP can obtain composites with significant electrical conductivity, maintaining the enhanced mechanical properties, at a lower cost
Influence of Fe2O3 content on the dielectric behavior of aluminous porcelain insulators
No full textDue to the increasing availability of substitute materials for electrical porcelain, research is needed to adapt formulations involving these materials to the current economic realities of the industry. This study assessed the effect of iron oxide concentration (0, 1, 2, 3, 5, and 8 wt%) on the dielectric properties of an aluminous porcelain composition commonly employed for electrical insulation based on different values of temperature and frequency. Samples with iron oxide contents of 0, 3, and 5 wt% were analyzed using dilatometry, X-ray diffraction, and scanning electron microscopy to evaluate the thermal, structural, and microstructural changes related to their Fe2O3 concentrations. Both the dielectric constant (epsilon(r)) and the loss tangent (tan delta) were measured and evaluated in every sample. Results indicated that the presence of Fe2O3 increased the dielectric constant and loss tangent, which could result in an increase in heating by dielectric losses. Fe2O3 contents of up to 5 wt% had no significant effect on the performance of these insulators at room temperature (similar to 30 degrees C) and a high frequency (1 MHz), especially when the hematite phase was completely solubilized in the porcelain phases. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved