Study and characterization of heat modified wood portuguese species

A modificação térmica tem-se revelado um método eficaz na melhoria da durabilidade de elementos de madeira. Até ao momento, as aplicações da madeira termicamente modificada (MTM) têm sido limitadas a revestimentos já que o tratamento térmico de tratamento conduz a uma redução significativa das resistências mecânicas da madeira. Contudo, este tratamento térmico poderá valorizar e potenciar a utilização de espécies de madeira menos utilizadas na construção, como são o Eucalipto e o Pinho bravo nacional. Com o objetivo de avaliar o efeito do tratamento térmico nas espécies referidas e, complementarmente, na madeira de Faia e Freixo, realizou-se uma campanha experimental composta por ensaios de caracterização mecânica (compressão paralela às fibras e flexão) e de estabilidade dimensional (retração, inchamento e teor de água de equilíbrio (TAE)). Para efeitos de comparação, todos os ensaios envolveram séries de provetes de cada espécie de madeira natural e MTM. Os resultados obtidos são coerentes com a bibliografia disponível, o aumento da estabilidade dimensional, assim como a diminuição do TAE e das propriedades mecânicas de flexão foram verificadas, permitindo, assim, avaliar a influência da modificação térmica nas propriedades de espécies de madeira presentes em Portugal.The thermal modification has proved to be an effective method to improve the durability of wood elements. Until the moment, applications of thermally modified wood (MTM) have been limited to non-structural applications, because the heat treatment leads to a significant reduction in the mechanical performance of wood. However, this heat treatment can promote the use of less used wood species in construction, as the national Eucalyptus and Pine. In order to evaluate the effect of heat treatment on the species of Pine, Eucalyptus, Beech and Ash, was held an experimental program that consisted in mechanical characterization tests (compression parallel to grain and flexion) and tests of dimensional stability (shrinkage, swelling and equilibrium moisture content (EMC)). For comparison, all tests were made with samples of non-modified and thermally modified wood. The results are consistent with the available literature, the dimensional stability increased, as well as the reduction of TAE and mechanical properties, allowing the evaluation of the thermal modification on the properties of wood species present in Portugal

Estudo e caracterização de espécies portuguesas de madeira termicamente modificada

A modificação térmica tem-se revelado um método eficaz na melhoria da durabilidade de elementos de madeira. Até ao momento, as aplicações da madeira termicamente modificada (MTM) têm sido limitadas a revestimentos já que o tratamento térmico de tratamento conduz a uma redução significativa das resistências mecânicas da madeira. Contudo, este tratamento térmico poderá valorizar e potenciar a utilização de espécies de madeira menos utilizadas na construção, como são o Eucalipto e o Pinho bravo nacional. Com o objetivo de avaliar o efeito do tratamento térmico nas espécies referidas e, complementarmente, na madeira de Faia e Freixo, realizou-se uma campanha experimental composta por ensaios de caracterização mecânica (compressão paralela às fibras e flexão) e de estabilidade dimensional (retração, inchamento e teor de água de equilíbrio (TAE)). Para efeitos de comparação, todos os ensaios envolveram séries de provetes de cada espécie de madeira natural e MTM. Os resultados obtidos são coerentes com a bibliografia disponível, o aumento da estabilidade dimensional, assim como a diminuição do TAE e das propriedades mecânicas de flexão foram verificadas, permitindo, assim, avaliar a influência da modificação térmica nas propriedades de espécies de madeira presentes em Portugal.The thermal modification has proved to be an effective method to improve the durability of wood elements. Until the moment, applications of thermally modified wood (MTM) have been limited to non-structural applications, because the heat treatment leads to a significant reduction in the mechanical performance of wood. However, this heat treatment can promote the use of less used wood species in construction, as the national Eucalyptus and Pine. In order to evaluate the effect of heat treatment on the species of Pine, Eucalyptus, Beech and Ash, was held an experimental program that consisted in mechanical characterization tests (compression parallel to grain and flexion) and tests of dimensional stability (shrinkage, swelling and equilibrium moisture content (EMC)). For comparison, all tests were made with samples of non-modified and thermally modified wood. The results are consistent with the available literature, the dimensional stability increased, as well as the reduction of TAE and mechanical properties, allowing the evaluation of the thermal modification on the properties of wood species present in Portugal

Thermal modification of most representative Portuguese wood species. A preliminary study

The thermal modification has proved to be an effective method to improve the durability of wood elements. Until now, most applications of thermally modified wood have been limited to non-structural applications since the wood’s heat treatment leads to a significant reduction in mechanical performances. However, there is no knowledge about these treatments applied on the wood species more used in Portuguese constructions. In order to evaluate the effect of heat treatment on the wood species of Maritime pine (Pinus pinaster), Eucalyptus (Eucalyptus globulus), Beech (Fagus sylvatica), Acacia (Acacia melanoxylon) and Oak (Quercus faginea), an experimental program consisted of mechanical bending tests and dimensional stability tests (shrinkage, swelling and equilibrium moisture content) was defined. For comparison purposes, all tests were made with test specimens of non-modified and thermally modified wood using four temperature values (200ºC, 240ºC, 260ºC and 300ºC) and three exposed periods (2, 4 and 8 hours). The obtained results show that the behaviour of the studied experimented species was similar to the one of other species already studied in the available literature. It was possible to point out that mechanical properties decrease with the severity of the thermal treatment, while the dimensional stability improved.The support given by Portuguese industry Santos & Santos through the supply of the wood specimens used in the experimental campaign is acknowledged

Cutinase purification on poly(ethylene glycol)–hydroxypropyl starch aqueous two-phase systems

The partition behaviour of cutinase on poly(ethylene glycol) (PEG)–hydroxypropyl starch aqueous two-phase systems was characterized. The effect of molecular mass of PEG, the pH of the system and tie-line length on cutinase partition coefficient and cutinase yield to the top phase was investigated for systems prepared with a purified hydroxypropyl starch (Reppal PES 100) and a crude one (HPS). The effect of the presence of different salts, such as sodium chloride, sodium sulphate and ammonium sulphate, on cutinase partition was also studied. The results lead to the conclusion that aqueous two-phase systems composed of PEG and hydroxypropyl starch are not efficient in the purification of cutinase. In the majority of cases, the partition coefficients were very close to 1, with pH being the factor which affects most cutinase partition. Partition coefficients were significantly improved when salts were added to the systems. For PEG 4000–Reppal PES 100 [at pH 4.0; 0.5 M (NH4)2 SO4], the partition coefficient for cutinase was 3.7, while a value of 12 was obtained for PEG 4000–HPS (at pH 4.0; 1 M NaC1). An isoelectric point (pI ) of 7.8 was confirmed for cutinase by constructing a cross partition graphic from the results obtained in the experiments with different salts. 1998 Elsevier Science B.V. All rights reserved

Systems for superficial protection of concretes

Nowadays, it is consensual that the biggest degradation of concrete happens from outside to inside actions, due to the penetration of moisture, active gases and aggressive ions, by mechanical, physical and chemical causes that frequently act together. A low porosity, permeability and concrete penetration to moisture and gases are the first lines of defence against several deterioration mechanisms. The durability of concrete depends largely on how hard or easy fluids (water, carbon dioxide, oxygen) in liquid or gas form can migrate through the concrete hardened mass. When selecting the paint coating for concrete protection, importance is given to the properties of diffusion and permeability resistance, besides the properties of durability and chemical resistance. The paint coatings must stop the penetration of water and delay the influence of aggressive agents (CO2, SO2, Cl- ions), allowing the structure to breathe by a water vapour diffusion mechanism. Through tests of capillarity absorption, immersion absorption, porosity, water and oxygen permeability, a comparison was made between painted and non painted concrete specimens. Three different coating types were tested: silicon varnish; acrylic and epoxy paints. The results showed that, in general, all coatings reduce the porosity and the permeability. The epoxy paints proved to be the best ones

Synthesis of pyridazine derivatives by Suzuki-Miyaura cross-coupling reaction and evaluation of their optical and electronic properties through experimental and theoretical studies

A series of π-conjugated molecules based on pyridazine and thiophene heterocycles 3a-e were synthesized using commercially or readily available coupling components, through a palladium catalyzed Suzuki-Miyaura cross-coupling reaction. The electron-deficient pyridazine heterocycle is functionalized by a thiophene electron-rich heterocycle at position 6 and different (hetero)aromatic moieties (phenyl, thienyl, furanyl) are functionalized with electron acceptor groups at position 3. DFT calculations were carried out to obtain information on the conformation, electronic structure, electron distribution, dipolar moment, and molecular nonlinear response of the synthesized push-pull pyridazine derivatives. Hyper-Rayleigh scattering in 1,4-dioxane solutions using a fundamental wavelength of 1064 nm was used to evaluate their second-order nonlinear optical properties. The thienylpyridazine functionalized with the cyano-phenyl moiety exhibited the largest first hyperpolarizability (beta = 175 × 10-30 esu, using the T convention) indicating its potential as a second harmonic generation (SHG) chromophore.The authors thank the Fundação para a Ciência e Tecnologia (Portugal) and FEDER-COMPETE for financial support through the Centro de Química and Centro de Física das Universidades do Minho e do Porto in the framework of the Strategic Funding (UID/QUI/0686/2016 and UID/FIS/04650/2013). Thanks are also due to Fundação para a Ciência e Tecnologia (FCT) for a Ph.D. grant to Sara S. M. Fernandes (SFRH/BD/87786/2012). This work was also supported by the Associated Laboratory for Sustainable Chemistry—Clean Processes and Technologies—LAQV which is financed by Portuguese national funds from FCT/MEC (UID/QUI/50006/2013) andco-financedbytheERDFunderthePT2020PartnershipAgreement(POCI-01-0145-FEDER–007265). TheNMR spectrometers are part of the National NMR Network (PTNMR) and are partially supported by Infrastructure Project Nº 022161 (co-financed by FEDER through COMPETE 2020, POCI and PORL and FCT through PIDDAC). The pulsed laser system was acquired within the framework of the grant (PTDC/CTM/105597/2008) from the Fundação para a Ciência e Tecnologia (FCT) with funding from FEDER-COMPETE.info:eu-repo/semantics/publishedVersio

Unified description of the dc conductivity of monolayer and bilayer graphene at finite densities based on resonant scatterers

We show that a coherent picture of the dc conductivity of monolayer and bilayer graphene at finite electronic densities emerges upon considering that strong short-range potentials are the main source of scattering in these two systems. The origin of the strong short-range potentials may lie in adsorbed hydrocarbons at the surface of graphene. The equivalence among results based on the partial-wave description of scattering, the Lippmann-Schwinger equation, and the T-matrix approach is established. Scattering due to resonant impurities close to the neutrality point is investigated via a numerical computation of the Kubo formula using a kernel polynomial method. We find that relevant adsorbate species originate impurity bands in monolayer and bilayer graphene close to the Dirac point. In the midgap region, a plateau of minimum conductivity of about $e^2/h$ (per layer) is induced by the resonant disorder. In bilayer graphene, a large adsorbate concentration can develop an energy gap between midgap and high-energy states. As a consequence, the conductivity plateau is supressed near the edges and a "conductivity gap" takes place. Finally, a scattering formalism for electrons in biased bilayer graphene, taking into account the degeneracy of the spectrum, is developed and the dc conductivity of that system is studied.Comment: 25 pages, 13 figures. published version: appendixes improved, references added, abstract and title slightly changed, plus other minor revision

Crossover to the Anomalous Quantum Regime in the Extrinsic Spin Hall Effect of Graphene

Recent reports of spin-orbit coupling enhancement in chemically modified graphene have opened doors to studies of the spin Hall effect with massless chiral fermions. Here, we theoretically investigate the interaction and impurity density dependence of the extrinsic spin Hall effect in spin-orbit coupled graphene. We present a nonperturbative quantum diagrammatic calculation of the spin Hall response function in the strong-coupling regime that incorporates skew scattering and anomalous impurity density-independent contributions on equal footing. The spin Hall conductivity dependence on Fermi energy and electron-impurity interaction strength reveals the existence of experimentally accessible regions where anomalous quantum processes dominate. Our findings suggest that spin-orbit-coupled graphene is an ideal model system for probing the competition between semiclassical and bona fide quantum scattering mechanisms underlying the spin Hall effect