Browsing by Author "Pereira, Helena"
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- Alternative species for the forest industry as forms of diversify the landscapePublication . Santos, António J.; Simões, Rogério; Pereira, Helena; Anjos, O.Together the forest and industrial activities within the Portuguese forest sector have a great importance in the national economy. The most used wood species in Portugal for industry (wood panel, sawmill, wood crates) are pine and eucalypt, which leads to extreme dependence and competition between the various industries for the same material, and thus unsustainable pressure on these forest resources. This is one of the causes of the decrease of pinewood area in recent years. On the other hand, this dependence leads to extensive areas of forest monocultures and, subsequently, increased risk of the forest fire propagation. This work intends to stimulate the diversification of the wood products used in the national industry of pulp and to provide a pulp with appropriate characteristics for incorporation as fibber for paper reinforcement. At the level of forest producers, the use of this prime-material would increase competitiveness among tree species and revitalization of less favoured rural areas and, turning them into a possible solution for the lack of wood and an incentive to the reforestation of these areas. Wood from species Cupressus sempervirens and Cupressus arizonica, Acacia delbata and Acacia melanoxylon were analysed. Content of extractives and of Klason lignin, fibre length and coarseness were determined. Representative wood samples from Pinus pinaster grown in Portugal and from Pinus sylvestris grown in Finland were used as reference. The wood from Cupressus sempervirens showed lower Klason lignin and a fibre quality that appears to be more adequate to pulp and paper. Acacia species, with their relatively short, flexible and collapsible fibres, have potential to produce papers with good relationships light scattering/tensile strength and smoothness/tensile strength, at low energy consumption in refining. The studied acacia species showed slightly better performance in pulping than the Eucalyptus globulus sample used as a comparison.
- Aplicação de espectroscopia de infravermelho próximo (NIR) na determinação da densidade básica em estilha de Acacia melanoxylon (R. Br.)Publication . Santos, António J.; Alves, Ana; Simões, Rita; Simões, Rogério; Anjos, O.; Tavares, Mário; Nunes, Lina; Knapic, Sofia; Pereira, Helena; Rodrigues, José CarlosO género Acácia inclui numerosas espécies, algumas economicamente importantes, que ocorrem naturalmente em zonas áridas na Austrália, Ásia, África e América. Em Portugal espécies destes género foram introduzidas no início do século XX, em solos secos e arenosos ao longo da costa. A Acacia melanoxylon apesar de bem adaptada às condições ecológicas do país, não tem sido aproveitada, em parte devido ao desconhecimento das suas propriedades.
- Caracterização da variação da espessura dos anéis de crescimento em Pinheiro BravoPublication . Pereira, Helena; Margarido, Marta; Pinto, Isabel; Usenius, Arto; Anjos, O.Com este trabalho pretende-se dar um contributo para o estudo dos factores de variação radial e axial da espessura dos anéis de crescimento de pinheiro bravo. O trabalho foi desenvolvido com base em técnicas de análise de imagem e tem como objectivo final incluir a variação dos anéis de crescimento na qualidade dos produtos finais serrados da madeira desta espécie. A informação para o estudo da variação das camadas de crescimento baseou-se numa amostra de tiras radiais e de discos nos níveis de altura 0, 5, 10, 15, 17 e 20 m de árvores de quatro estações em Portugal. A amostragem em discos permitiu a medição das camadas de crescimento em várias direcções e a posterior criação de um modelo tridimensional do tronco com base nos anéis de crescimento. A variação das camadas de crescimento foi analisada em sequência vertical, onde se analisam os anéis de crescimento em cada nível, obtendo-se assim o crescimento das árvores e quais as suas variação ao longo do tempo, e em sequência oblíqua onde se pode analisar o comportamento dos 13 anos terminais ao longo da árvore. Efectuou-se uma análise de variância para diferentes factores onde se contabilizou a percentagem de variação correspondente a cada um desses factores. Verificou-se que a maior parte da variação se deve à variação lenho juvenil/lenho adulto. O modelo tridimensional do tronco foi desenvolvido numa interface que permite observar a variação das camadas de crescimento nas diferentes secções transversais a níveis de altura especificados. De futuro este modelo será integrado na reconstrução tridimensional já desenvolvida para o Pinheiro bravo e que descreve a geometria do tronco e os anéis internos. O objectivo final será o uso da informação sobre as camadas de crescimento em programas de simulação de serração de forma a constituir mais um parâmetro de qualidade dos produtos finais.
- Caracterização da variação da espessura dos anéis de crescimento em pinheiro bravoPublication . Margarido, Marta; Pinto, Isabel; Pereira, Helena; Usenius, Arto; Anjos, O.Com este trabalho pretende-se dar um contributo para o estudo dos factores de variação radial e axial da espessura dos anéis de crescimento de pinheiro bravo. O trabalho foi desenvolvido com base em técnicas de análise de imagem e tem como objectivo final incluir a variação dos anéis de crescimento na qualidade dos produtos finais serrados da madeira desta espécie. A informação para o estudo da variação das camadas de crescimento baseou-se numa amostra de tiras radiais e de discos nos níveis de altura 0, 5, 10, 15, 17 e 20 m de árvores de quatro estações em Portugal. A amostragem em discos permitiu a medição das camadas de crescimento em várias direcções e a posterior criação de um modelo tridimensional do tronco com base nos anéis de crescimento. A variação das camadas de crescimento foi analisada em sequência vertical, onde se analisam os anéis de crescimento em cada nível, obtendo-se assim o crescimento das árvores e quais as suas variação ao longo do tempo, e em sequência oblíqua onde se pode analisar o comportamento dos 13 anos terminais ao longo da árvore. Efectuou-se uma análise de variância para diferentes factores onde se contabilizou a percentagem de variação correspondente a cada um desses factores. Verificou-se que a maior parte da variação se deve à variação lenho juvenil/lenho adulto. O modelo tridimensional do tronco foi desenvolvido numa interface que permite observar a variação das camadas de crescimento nas diferentes secções transversais a níveis de altura especificados. De futuro este modelo será integrado na reconstrução tridimensional já desenvolvida para o Pinheiro bravo e que descreve a geometria do tronco e os anéis internos. O objetcivo final será o uso da informação sobre as camadas de crescimento em programas de simulação de serração de forma a constituir mais um parâmetro de qualidade dos produtos finais.
- Characterization and within-tree variation of wood anatomy of Acacia melanoxylonPublication . Santos, António J.; Pereira, Helena; Anjos, O.Introduction: 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. Conclusions: Blackwood showed potential as an alternative species to supply the industry.
- Characterization of cypress wood for kraft pulp productionPublication . Santos, António J.; Anjos, O.; Morais, Maria Cristina; Diogo, Maria da Graça; Simões, Rogério; Pereira, HelenaWood samples of Cupressus arizonica, C. lusitanica, and C. sempervirens were evaluated for chemical, anatomical, and pulp characteristics as raw material for pulp production. Two 17-year-old trees per species were harvested, and wood samples were taken at a height of 2 m. Wood chips from Pinus pinaster (Portugal) and P. sylvestris (Finland) were used as references. C. arizonica differed from C. lusitanica and C. sempervirens with significantly lower (p < 0.05) tracheid diameter and wall thickness in the earlywood. The total extractives contents were 3.9%, 3.3%, and 2.5% for C. lusitanica, C. sempervirens, and C. arizonica, respectively, lower than the 5.1% for P. pinaster and 4.5% for P. sylvestris. Klason lignin content ranged from 33.0 to 35.6%, higher than the 28.0 to 28.7% for the pinewoods. The kraft pulp yields for C. arizonica, C. lusitanica, and C. sempervirens were 37.7%, 36.7%, and 38.7%, respectively, with kappa numbers of 32.0, 31.6, and 28.7, respectively; the yield values were 40.8% and 42.8%, with kappa numbers of 23.4 and 21.0, for P. pinaster and P. sylvestris, respectively. The cypress species are clearly different from pine in relation to wood pulping behavior. Among the cypress, C. sempervirens provided the best pulping results
- Characterization of radial bending properties of corkPublication . Anjos, O.; Pereira, Helena; Rosa, Maria EmíliaThe behaviour of cork under three point bending stress in the radial direction was evaluated in relation to porosity (range 2.0–15.4%) and density (range 0.160– 0.220 g cm−3). The study was made using water-boiled cork planks of two commercial quality classes (good and poor quality) collected at an industrial mill. Cork samples were cut with the largest dimension in two directions, axial and tangential, and with the load zone in the inner part and the outer part of the plank. The stress-strain curves obtained in bending were similar for the different test specimens and similar to those observed for tensile tests in cork but the mechanical resistance of cork in bending was higher than in tension and lower than in compression. The direction of the internal stress in samples submitted to bending was a highly significant factor of variation. The curves showed an initial linear elastic region with a mean Young’s modulus of 14 MPa for the tangential direction and 21 MPa for the axial direction, followed by a region of a gradual cork yielding up to a peak load, and failure at an average stress of 1.2 MPa and a strain of 14%. There was significant difference in the bending properties of cork samples obtained from cork planks of different quality classes. Density and porosity were not individually well correlated with the mechanical parameters. It was however possible to model Young’s modulus by combining porosity and density.
- Controlo de qualidade do mel de rosmaninho: comparação do desempenho de FTIR-ATR e FT-RamanPublication . Santos, António J.; Estevinho, Letícia M.; Pereira, Helena; Anjos, O.
- Effect of density on the compression behaviour of corkPublication . Anjos, O.; Rodrigues, Cátia; Morais, José; Pereira, HelenaThe compression properties of cork were studied for samples of different density. The densities were grouped into three classes: low density (0.13–0.15), mid density (0.15–0.19) and high density (0.19–0.25). The porosity of the cork samples increased from the low to the high density class, with porosity coefficients of 5.1%, 6.9% and 9.4%, respectively. The difference in the porosity was associated with structural features, namely the presence of thick walled cork cells and the presence of lignified cells lining the pores. The stress–strain curves were similar for all cases, showing an elastic compression up to a yield point of about 5% strain, followed by a plateau with a small slope. The cork strength was higher in the radial direction than in the other directions. The density influenced the compression such that the corks with high density presented higher stiffness in compression in three directions: Young’s modulus was 17.4, 22.6 and 26.1 MPa for low, mid and high density corks respectively. This density effect was more evident in the plateau region of the progressive buckling of the cell walls (σ30 was respectively 1.07, 1.29 and 1.54 MPa for the three density classes). The recovery of dimensions after compression in each direction was also studied following compression to 50% strain. The recovery was on average 50% of the initial deformation on the first day, and almost total after 15 days. The recovery was higher for corks with low density and in non-radial directions..
- Effect of quality, porosity and density on the compression properties of corkPublication . Anjos, O.; Pereira, Helena; Rosa, Maria EmíliaThe compression properties of cork were studied on samples obtained from cork planks of two commercial quality classes (good and poor quality), with densities ranging from 0.12–0.20g cm-3 and porosities from 0.5 to 22.0%. The stress-strain curves were characterized by an elastic region up to approximately 5% strain, followed by a large plateau up to 60% strain caused by the progressive buckling of cell walls, and a steep stress increase for higher strains corresponding to cell collapse. The direction of compression was a highly significant factor of variation, with cork showing higher strength for the radial compression. Density influenced compression and cork samples with higher density showed overall larger resistance to compression in the three directions. In the elastic region, an exponential model of Young’s modulus in function of cork density could be adjusted. The effect of porosity on compression was small and the stress-strain curves were similar regardless of the porosity of the samples, although there was a trend toward an overall increase of stress with porosity for higher strains. Porosity was characterised by a high variability in the anatomical features of the lenticular filling material and the presence of collapsed and thick walled lignified cells. The inclusion of a porosity parameter for the modelling of the elastic modulus did not improve the prediction obtained with density-based models. There was no significant difference in the compression properties of cork samples obtained from cork planks of good and poor quality classes.