Browsing by Author "Pereira, Helena"
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- Characterization and within-tree variation of wood anatomy of Acacia melanoxylonPublication . Santos, António; Pereira, Helena; Anjos, OféliaIntroduction: A. melanoxylon wood has a large commercial application given its anatomical characteristics and mechanical properties. However studies on the anatomical characterisation of this species grown in Portugal are scarce. Objectives: To describe the transverse anatomical characteristics and their within-tree variation of A. melanoxylon trees growing in Portugal. Methods: 20 trees were analysed in transverse section for tree radial position (10%; 50%; 90%) and five height levels (base, 15%; 35%; 65%; 80%) in north and south directions. Measurements included: fibre diameter (m), fibre wall thickness (m), Runkle index; Flexibility index, vessel number (vessel number /mm2), porosity (%) and vessel width (m). Results: Earlywood fibres have lower wall thickness and higher lumen diameter than latewood fibres. Runkle and flexibility indexes confirm its potential for pulp and paper production. Porosity was lower near the pith as a result of a slight increase of vessel number with smaller size. Conclusion: Blackwood showed potential as an alternative species to supply the industry.
- Chemical characterization, bioactive and fuel properties of waste cork and phloem fractions from Quercus cerris L. barkPublication . Sen, Ali; Miranda, Isabel; Esteves, Bruno; Pereira, HelenaWaste biomass composed of cork-rich and phloem-rich granules obtained from the fractioning of Quercus cerris L. bark were characterized for bulk density, chemical composition, bio-active components, ash composition, and higher heating value. Bulk density of the fractions relate to their cork content and deceases with smaller particle size due to a cork enrichment in the finer particles. The bulk density may therefore be used as an indicator of suberin content of waste cork and phloem fractions. Waste cork fractions are rich sources of lipophilic and polar extracts while waste phloem fractions contain high amount of polar extracts. The polar extracts of both biomass fractions showed very high antioxidant capacities with IC50 values between 2.5 and 7.3 μg extract mL-1 for cork fractions and 5.8 and 11.7 μg extract mL-1 for phloem fractions. Higher heating values in waste cork fractions increase with decreasing particle size and ranged between 20 and 22 MJ kg-1. A biorefinery scheme was developed for the valorization of the waste cork and phloem fractions based on their physical, chemical, bioactive, and higher heating values
- Chemical effects of a mild torrefaction on the wood of eight Eucalyptus speciesPublication . Araújo, Solange de Oliveira; Neiva, Duarte M.; Gominho, Jorge; Esteves, Bruno; Pereira, HelenaThe torrefaction is a thermal pre-treatment to improve biomass quality for biofuel applications. In this study, the effects of a mild torrefaction (T) on eight euca- lypt species ( Eucalyptus botryoides, E. globulus, E. grandis, E. maculata, E. propinqua, E. rudis, E. saligna and E. vimi- nalis ) have been compared. Namely, the mass loss (ML), the equilibrium moisture content (EMC), density and chemical composition were determined and FTIR spectra were recorded of the initial and torrefied woods (TWs). The average ML was 11% and the heat-treated woods had an overall 10% density decrement. All the TW had 50% lower EMC compared to untreated wood samples (W). Elemen- tal composition showed that carbon content increased from 48% to 53% and the oxygen/carbon ratio decreased from 0.80 to 0.65. The chemical changes induced by T included an increment of extractives, a 20% higher lignin content and a 16% lower holocellulose content in relation to W. The hemicelluloses modification is manifested by a decrease of xylose, galactose, and acetyl groups in TWs. The fourier transform infrared (FTIR) spectra of the different wood species were very similar, and reflected in a uniform manner the chemical changes upon T. Because of the similar reaction of the eucalypt species, they can also be used in form of mixed eucalypt feedstock as biofuel.
- Chemistry and ecotoxicity of heat-treated pine wood extractivesPublication . Esteves, Bruno; Videira, Romeu; Pereira, HelenaPine (Pinus pinaster) wood was heat treated in an autoclave for 2-12 hours at 190-210 ºC. Hemicelluloses were the first compounds affected by the treatment. In general, the sugar decrease was higher for arabinose and galactose followed by xylose and mannose. Lignin started to degrade for small mass losses but at a slower rate than hemicelluloses, and cellulose only degraded significantly for severe treatments. Almost all of the original extractives disappeared and new compounds arose like anhydrosugars and phenolic compounds. The compounds that might leach from heat treated wood were mainly those identified in the water and ethanol extracts, all of which were not harmful at the existing concentrations, thereby reinforcing the wood heat treatment as an environmental benign process.
- Colagem e propriedades mecânicas da madeira de pinheiro tratada termicamentePublication . Esteves, Bruno; Pereira, HelenaO tratamento térmico da madeira permite diminuir a higroscopicidade da madeira, melhorando a sua estabilidade dimensional e a resistência a vários tipos de biodegradação. Utilizando este tratamento é possível atribuir um maior valor acrescentado, permitindo a madeiras menos nobres a sua utilização no exterior, sem a utilização de qualquer químico. O tratamento térmico da madeira de pinheiro (Pinus pinaster) foi feito na ausência de oxigénio numa autoclave com uma mistura de ar sobreaquecido e saturado durante 2, 4, 6, 8 e 12 horas à temperatura de 200 ºC. Determinou-se a resistência à colagem, a molhabilidade e a dureza nas secções tangencial e radial, o módulo de elasticidade e a tensão de rotura por flexão estática. A resistência à colagem, utilizando uma cola de acetato de polivinil (PVA) foi determinada de acordo com a norma DS/CEN/TS 13354. Determinou-se a molhabilidade da madeira pelo método do ângulo de contacto usando um goniómetro. A dureza foi medida de acordo com a norma ISO 3350 (1975). O módulo de elasticidade e a tensão de rotura à flexão foram determinados através de um ensaio a três pontos. Verificou-se que a resistência à colagem diminuiu com a intensidade do tratamento térmico. Foi possível obter uma relação aproximadamente linear (R2=0,81) entre a resistência à colagem e a perda de massa devido ao tratamento térmico. Ao mesmo tempo observou-se uma diminuição da molhabilidade da superfície da madeira o que contribui para uma diminuição da resistência à colagem. Em relação às propriedades mecânicas o MOE praticamente não foi afectado enquanto a tensão de rotura diminuiu com a intensidade do tratamento atingindo cerca de menos 30%. A dureza da madeira tratada também diminuiu quer na secção tangencial, quer na radial atingindo uma redução máxima de cerca de 30%.
- Comparison between heat treated sapwood and heartwood from Pinus pinasterPublication . Esteves, Bruno; Nunes, Lina; Domingos, Idalina; Pereira, HelenaSapwood and heartwood samples of Pinus pinaster were treated in an oven at 190ºC and 200ºC for 2-6h. Dimensional stability, measured as Anti Shrinking Efficiency (ASE) between 0% and 65% relative humidity, durability against fungi, mechanical resistance (MOE and MOR), hardness and chemical composition were determined for treated and untreated sapwood and heartwood. Radial ASE reached 52% for sapwood and 50% for heartwood while tangential ASE reached 50% and 40% respectively. MOE increased slightly at the beginning of the treatment decreasing afterwards. No significant differences were found between sapwood and heartwood. MOR decreased by 50% and 30% for sapwood and heartwood respectively. A significant increase in durability against Rhodonia placenta was found for both heartwood and sapwood at the higher temperature and for heartwood only at 190º for 4h.
- Cork Liquefaction for Polyurethane Foam ProdutionPublication . Esteves, Bruno; Dulyanska, Yuliya; Costa, Catarina; Vicente, Jose; Domingos, Idalina; Pereira, Helena; Lemos, Luis; Cruz-Lopes, LuísaCork is one of the most important forest products in Portugal. The cork processing industry is highly resource-efficient, with the only residue, cork powder, which is too minor in quantity for agglomerate production. This work studied the usage of cork powder for the production of added-value products via polyol liquefaction. Liquefactions were performed in a reactor using a mixture of polyethylene glycol (PEG 400) and glycerol as solvents, which were catalyzed by the addition of sulphuric acid. Several cork-to-solvent ratios, reaction temperatures, and reaction times were tested. Polyurethane foams were prepared by combining polyol mixtures with a catalyst, surfactant, blowing agent, and polymeric isocyanate. Mechanical tests of the produced foams were conducted, and compressive modulus of elasticity and compressive stress at 10% deformation were determined. The results show that the best conditions for obtaining high liquefaction yields are as follows: 160 ºC for 1 h; glycerol-to-PEG 400 ratio of 1:9; cork-to-solvent ratio of 1:6; and 3% H2SO4 catalyst addition. The Fourier Transform Infrared (FTIR) spectra indicated that the lignocellulosic fractions of the cork were more selectively dissolved during acidified polyol liquefaction than the suberin. With liquefied cork powder using these optimized conditions, it is possible to produce polyurethane foams with desired properties.
- Heat-treated wood as chromium adsorption materialPublication . Esteves, Bruno; Cruz-Lopes, Luísa; Figueirinha, Artur; de Lemos, Luis Teixeira; Ferreira, José; Pereira, Helena; Domingos, IdalinaHeavy metals adsorption with lignocellulosic materials has been heavily researched in the last years. Since heat activation has been used with good results to increase the adsorption capacity of some materials, heat-treated wood might be a better adsorbent. This hypothesis is the basis of the present study. The adsorption tests were made with powdered pine wood, heat-treated at 190–210 °C. All the heat-treated samples showed a significantly higher adsorption compared to untreated wood. The maximum adsorption was obtained at pH 3 for heat-treated wood at 210 °C. The kinetics of the adsorption process fitted a pseudo-second-order reaction (R2 0.990–0.996). Adsorption fitted well both the Langmuir and the Freundlich model, but the Freundlich model presented higher R2 (0.988–0.998). The qmax values estimated by the Langmuir plotting were in the range 15.6–19.4 mg/g and the n values from Freundlich isotherms between 1.87 and 2.39. Heat-treated wood was a better adsorption material than untreated wood for chromium adsorption. This can be a good application for the sawdust produced by the processing of heat-treated wood at primary and secondary wood processing mills or for the recycling of heat-treated wood at the end of product life.
- Improvement of termite resistance, dimensional stability and mechanical properties of pine wood by paraffin impregnationPublication . Esteves, Bruno; Nunes, Lina; Domingos, Idalina; Pereira, HelenaParaffin has been used as surface protection of wood throughout the ages but its use for impregnation to improve wood resistance to biodegradation is recent. This study determined the main improvements on wood properties with paraffin impregnation. Healthy Pinus pinaster Ait. wood was impregnated with paraffin at different levels using a hot–cold process. Weight gain, equilibrium moisture content and dimensional stability (ASE) at 35 and 65 % relative humidity, termite durability against Reticulitermes grassei (Clément), bending strength, bending stiffness (MOE) and Janka hardness were determined. Density increased from 0.57 to 0.99, ASE ranged between 38–96 % and 16–71 % for 35 and 65 % relative humidity, respectively. Equilibrium moisture content decreased from 9.9 and 12.0 % to 0.8 and 3.6 % for 35 and 65 % relative humidity. Termite durability improved from level 4 to level 3 of attack, and higher termite mortality was found in treated wood (52 % against 17 %). Bending strength (MOR) increased with paraffin weight gain, reaching a 39 % increase. MOE also increased by about 13 % for wood with a weight gain around 80 %. Janka hardness increased significantly reaching about 40 % for wood with 80 % weight gain. Paraffin impregnated wood has improved properties with regard to equilibrium moisture content, dimensional stability and density, bending strength and Janka hardness, and resistance against termites.
- Influence of Chemical Composition on Heating Value of Biomass: A Review and Bibliometric AnalysisPublication . Esteves, Bruno; Sen, Umut; Pereira, HelenaAbstract: Biomass has become an increasingly important resource for energy generation. The influence of the chemical composition on the heating value of biomass has not been a thoroughly studied subject, as shown by a bibliometric analysis. It is well known that the heating value of lignin is significantly higher (23.26–25.58 MJ/kg) than that of polysaccharides (18.6 MJ/kg), while extractives often have HHVs over 30 MJ/kg, depending on their oxidation levels. Therefore, the proportions of the chemical components in biomass determine its HHV. Softwoods generally have higher HHVs than hardwoods due to their higher contents of lignin and lipophilic resin. Ashes are incombustible, and a high ash content leads to a lower HHV in biomass. Several models have been proposed to correlate the heating values and chemical compounds of biomass, but the most accurate models are based on the lignin from extracted samples, while good correlations between lignin and extractives have also been reported. No good correlations have been obtained with polysaccharide compounds.