Helena Pereira | Instituto Superior De Agronomia (original) (raw)

Papers by Helena Pereira

Research paper thumbnail of O montado e a cortiça. Livro de Resumos

A regeneração natural do sobreiro inicia-se com a germinação de plântulas, após a queda das bolot... more A regeneração natural do sobreiro inicia-se com a germinação de plântulas, após a queda das bolotas. Estas plântulas estabelecem-se, crescem e formam árvores que continuarão o ciclo da regeneração florindo, frutificando e produzindo novas bolotas. Ao longo deste processo vários factores podem limitar o recrutamento de jovens árvores. Apesar da produção de bolota variar entre árvores e anos, e as bolotas serem muito predadas e terem longevidade curta, a limitação do recrutamento não se deve, em geral, à escassez de sementes mas concentra-se nos dois primeiros anos de vida.

Research paper thumbnail of ¿Qué hay que tener en cuenta para elaborar modelos de producción de corcho?: revisión bibliográfica y consideraciones estadísticas

Research paper thumbnail of Modelo de crecimiento en diámetro para alcornocales del centro y sur de Portugal

Los modelos presentados son modelos de árbol individual en los que se analiza la influencia de la... more Los modelos presentados son modelos de árbol individual en los que se analiza la influencia de las dimensiones del individuo, la gestión aplicada en el descorche y la competencia intraespecífica en el crecimiento diametral. La variable independiente es el crecimiento medio en circunferencia bajo corcho calculado por diferencia de dos mediciones tomadas en intervalos de nueve o diez años. La estructura inicial del modelo es la de un modelo mixto con efectos fijo de intervalo de medición (9 o 10 años) y de región y efecto aleatorio de parcela. La variable dependiente que más variabilidad explica es la intensidad de descorche. El efecto regional es significativo a diferencia del efecto parcela, por lo que el modelo final seleccionado es un modelo de efectos fijos. El índice independiente de la distancia "Área de crecimiento proporcional al diámetro" es el de mejor comportamiento. Dentro de los dependientes de la distancia el de "Distancia ponderada por dimensiones" ...

Research paper thumbnail of Variation of lignin monomeric composition during kraft pulping of Eucalyptus globulus heartwood and sapwood

Journal of Wood Chemistry and Technology, 2012

Heartwood and sapwood samples from Eucalyptus globulus were characterized by Py-GC/MS and GC-FID ... more Heartwood and sapwood samples from Eucalyptus globulus were characterized by Py-GC/MS and GC-FID in respect to composition and content of lignin. The pyrolysis lignin-derived compounds were assembled by groups: “syringol,” “S-aldehydes,” “S-ketones,” “S-alcohols,” and “C11H12O3” (S-units); “guaiacol,” “eugenol,” “G-aldehydes,” “G-ketones,” “G-alcohols,” and “others” (G-units); “phenol” and “H-aldehydes” (H-units). Heartwood and sapwood had similar lignin content in an extractive-free basis (23.7% and 23.0%, respectively) and in lignin composition (S-units, 76.0% vs. 76.3%; G-units, 22.0% vs. 21.0%; H-units, 1.9% vs. 2.7%; S/G ratio 3.5 and 3.6). The wood samples were kraft pulped under isothermal conditions at 130°C, 150°C and 170°C and several cooking times. Heartwood and sapwood behaved similarly. At 130°C the delignification was slow with no significant selectivity in respect to lignin composition. At 150°C and 170°C the S-units were more susceptible to reaction and comparatively more removed, inducing a decrease of S/G ratio to 0.6. The main products to be extracted belong to “syringol” and “S-aldehydes,” while the residual lignin in pulps was enriched in “guaiacol,” “eugenol” (G-units), and “phenol” (H-units).

Research paper thumbnail of ANATOMICAL CHARACTERISATION AND VARIABILITY OF THE THISTLE CYNARA CARDUNCULUS IN VIEW OF PULPING POTENTIAL

The thistle Cynara cardunculus L. is an herbaceous perennial with high productivity that is harve... more The thistle Cynara cardunculus L. is an herbaceous perennial with high productivity that is harvested annually and is a potential fibre crop for paper pulp production. The anatomical variation within stalks was studied (base, middle and top) and compared in C. cardunculus plants at different development phases. The stalk of C. cardunculus includes an epidermis, cortex and a central cylinder with fibro-vascular bundles with phloem, xylem and a fibrous sheath that is variable in arrangement and size within and between plants. At harvest, the pith represents 37% of the stalk transectional area and 7% of the total weight. There was a slight variation in quantitative features of, respectively, the three development groups studied; mean fibre length was 1.04 mm, 0.95 mm and 1.05 mm; mean fibre width was 15 μm, 16 μm and 21 μm; mean fibre wall thickness was 3.2 μm, 3.4 μm and 4.9 μm. Fibre length and width decreased within the stem from base to top, while fibre wall thickness increased. Mean vessel diameter was 22 μm and mean vessel element length 220-483 μm. In mature plants, parenchyma represents 39% of the total transectional area and fibres 25%. The proportion of fibres increases during plant development and in mature plants is highest at the stalk base. As regards anatomical features, Cynara stalks compare favourably to other annual plants and fibre biometry indicates good potential for paper sheet forming and strength properties.

Research paper thumbnail of Reactivity of syringyl and guaiacyl lignin units and delignification kinetics in the kraft pulping of Eu-calyptus globulus wood using Py-GC-MS/FID.

Eucalyptus globulus sapwood and heartwood showed no differences in lignin content (23.0% vs. 23.7... more Eucalyptus globulus sapwood and heartwood showed no differences in lignin content (23.0% vs. 23.7%)
and composition: syringyl-lignin (17.9% vs. 18.0%) and guaiacyl-lignin (4.8% vs. 5.2%). Delignification kinetics of S- and G-units in heartwood and sapwood was investigated by Py-GC–MS/FID at 130, 150 and 170 ºC and modeled as double first-order reactions. Reactivity differences between S and G-units
were small during the main pulping phase and the higher reactivity of S over G units was better expressed in the later pulping stage. The residual lignin composition in pulps was different from wood or from samples in the initial delignification stages, with more G and H-units. S/G ratio ranged from 3 to 4.5 when pulp residual lignin was higher than 10%, decreasing rapidly to less than 1. The S/H was initially around 20 (until 15% residual lignin), decreasing to 4 when residual lignin was about 3%.

Research paper thumbnail of Evaluation of beech wood defects due to different drying schemes

Drying above the fiber saturation point is pure water transport without shrinkage. Shrinkage star... more Drying above the fiber saturation point is pure water transport without shrinkage. Shrinkage starts from moisture content below the fiber saturation point. This is motivated by the fact with development of strain and stress, occurs only that point. The paper presents the results obtained in an experimental study concerning the influence of drying temperature on beech wood (Fagus sylvatica L.).

Research paper thumbnail of Incork. Avaliação da influência da estrutura interna na transmissão de oxigénio de rolhas de cortiça natural por técnicas não destrutivas

A avaliação da qualidade das rolhas de cortiça natural é feita actualmente por uma análise visual... more A avaliação da qualidade das rolhas de cortiça natural é feita actualmente por uma análise visual da sua superfície exterior utilizando sistemas automáticos de análise de imagem ou operadores. As rolhas de boa qualidade apresentam poucos poros de pequena dimensão, contrariamente às de menor qualidade com muitos poros ou poros de grande dimensão. Verificase, no entanto, que existe uma grande heterogeneidade das classes de qualidade em relação à taxa de transmissão de oxigénio, uma importante propriedade das rolhas de cortiça, definidora da sua capacidade como vedante. Os estudos existentes têm mostrado que a transmissão de oxigénio das rolhas naturais é independente dos parâmetros clássicos de valorização comercial, classe visual de qualidade, diâmetro, comprimento e massa volúmica. Estes resultados evidenciam a necessidade de identificar parâmetros críticos internos à superfície da rolha, responsáveis por classes de qualidade não homogéneas. O projeto de investigação INCORK tem como principal objectivo o desenvolvimento de uma nova forma de caracterizar as rolhas de cortiça natural, usando não só as suas características externas, mas também as suas características internas. Para atingir este objectivo procedeu-se à caracterização total da estrutura interna e externa de rolhas de cortiça natural, efectuando uma caracterização por análise de imagem da superfície exterior, bem como aplicando técnicas não destrutivas de caracterização de materiais, nomeadamente radiação terahertz e tomografia axial computorizada (TAC). O INCORK visa o desenvolvimento de um novo sistema integrado de avaliação não destrutiva da estrutura interna e da superfície exterior das rolhas de cortiça que permita optimizar a sua classificação do ponto de vista da qualidade e de transmissão de oxigénio.

Research paper thumbnail of Tensile properties of cork in axial stress and influence of porosity, density, quality and radial position in the plank

European Journal of Wood and Wood Products, Feb 1, 2011

The behaviour of cork under tensile stress in the axial direction was studied for samples taken f... more The behaviour of cork under tensile stress in the axial direction was studied for samples taken from cork planks of good (class 1) and poor (class 4) quality grades and at three radial positions within the plank (inner, mid and outer positions). The effect of cork density (ranging from 0.123 to 0.203 g.cm -3 ) and porosity (ranging from 2.8 to 9.6% in the tangential surface) on Young's modulus and fracture stress and strain was studied. The tensile stress-strain curves of cork showed an elastic deformation up to 2% strain with a Young's modulus of 30.8 MPa, and a fracture stress of 1.05 MPa at a strain of 7.1% for class1, and Young's modulus of 26.1 MPa, and a fracture stress of 0.77 MPa at a strain of 5.5 % for class 4. Fracture always started at a pore. The quality class and the radial position in the plank were highly significant factors of the tensile properties variation with good quality cork in the inner part of the plank showing the highest strength. Density influenced the elastic behaviour of cork with a highly significant correlation of increasing E with density, but not so clearly the fracture stress and strain. The variability of tensile properties with porosity was large and although significant, the correlations were lower in spite of a decreasing trend of E with porosity. Fracture depended on the type of defects in cork.

Research paper thumbnail of Definition of quality classes for champagne cork stoppers in the high quality range

Wood Science and Technology, 2000

For champagne and other sparkling wines, agglomerated cork stoppers are used, lined at the bottom... more For champagne and other sparkling wines, agglomerated cork stoppers are used, lined at the bottom with two superposed discs of natural cork. The quality evaluation of champagne stoppers in the high quality range was made in relation to the porosity of the visible surface of the bottom cork disc using image analysis techniques. The average porosity coef®cient was 3.1%. Most pores were small but approx. 75% of the total porosity comes from pores with an area >0.25 mm 2 . Pores with a high visual impact (>2.0 mm 2 ) are less than 1% and were not determinant to the total porosity. The quality grading could be made using porosity coef®cients as selection criteria to discriminate between classes. In comparison to commercial grading, the use of quanti®ed porosity parameters for quality class de®nition allowed higher within class homogeneity and between class differentiation.

Research paper thumbnail of Tensile properties of cork in the tangential direction : variation with quality, porosity, density and radial position in the cork plank

The behaviour of cork under tensile stress in the tangential direction was evaluated in relation ... more The behaviour of cork under tensile stress in the tangential direction was evaluated in relation with its structural characteristics. The study was made using raw cork planks of two commercial quality classes (class 1, good quality and class 4, poor quality) collected at one industrial mill after post-harvest six-month air stabilization. Cork samples were taken at three radial positions in the cork planks (outer, mid and inner part). The porosity of the samples was determined by image analysis on the surfaces parallel to the tensile stress. The tensile test used a crosshead speed of 5 mm min -1 , corresponding to a strain rate of 1.7 x10 -3 s -1 . Young's modulus was calculated from the average slope of the stress-strain curve between the loads of 10 N and 100 N, corresponding to strains between approximately 1% and 2.5%. The cork samples presented densities ranging 0.129-0.186 g.cm -3 and porosities ranging 2.9-10.7%. There was no significant difference in the tensile properties of cork samples obtained from cork planks of different quality classes. However, the radial position in the cork plank was a highly significant factor of variation in the tensile tests, with higher strength for the cork samples taken in the inner part. The tensile properties (Young's modulus, fracture stress and fracture strain) showed a good correlation with cork density. The porosity had a good correlation, but in inverse order, only for the good quality (class1) cork planks.

Research paper thumbnail of Análise espacial da mortalidade do sobreiro em S. Bartolomeu da Serra (Santiago do Cacém)

Resumo. Avaliou-se a distribuição espacial da mortalidade do sobreiro (Quercus suber L.) na área ... more Resumo. Avaliou-se a distribuição espacial da mortalidade do sobreiro (Quercus suber L.) na área da freguesia de S. Bartolomeu da Serra (Santiago do Cacém), integrada numa região em que ela ocorre com elevada incidência, através de técnicas de detecção remota (SIG), e determinou-se a probabilidade de ocorrência de mortalidade através da aplicação de um modelo de regressão logística. Determinou-se um índice de mortalidade e identificaram-se as unidades fisiográficas com maior probabilidade de mortalidade em três sistemas agroflorestais distintos: floresta de sobreiro (florestas densas), montado de sobro tradicional (florestas abertas em sistemas dominantemente agrícolas, com culturas arvenses sob coberto) e incultos (florestas abertas em sistemas dominantemente incultos, com matos sob coberto). A mortalidade do sobreiro é significativamente diferente para os três tipos de sistemas agro-florestais. A mortalidade é influenciada por características físicas da paisagem como o solo, o declive e a exposição. Em solos pouco profundos ou em solos mais compactos, a mortalidade é mais frequente, mostrando a importância do desenvolvimento radicular em profundidade do sobreiro em regiões susceptíveis a extensos períodos de secura. Palavras-chave: Quercus suber L., declínio do montado de sobro, detecção remota regressão logística, mortalidade do sobreiro *** POSTERS TEMA 1 125

Research paper thumbnail of Caracterização por pirólise (Py-GC/MS(FID)) do cerne, borne e pastas kraft de eucalipto

A Eucalyptus globulus é uma espécie muito usada para a produção de pasta para papel devido às sua... more A Eucalyptus globulus é uma espécie muito usada para a produção de pasta para papel devido às suas caracteristicas químicas, em particular o conteúdo e composição da lenhina. Para este trabalho, o cerne e o borne do eucalipto foram caracterizados por pirólise (Py-GC/MS(FID)). O cerne e o borne apresentaram conteúdos semelhantes em lenhina (L) e polissacáridos (C) , respectivamente 23,7% e 74,5% (cerne), 23,0% e 74,5% (borne), resultando num rácio C/L de 3,1 e 3,2. Para estudar a deslenhificação foram produzidas pastas kraft a 130, 150 e 170 ºC, durante vários tempos de cozimento (de 1 a 185 min). O efeito da temperatura na deslenhificação foi evidente: a lenhina foi removida lentamente a 130 ºC, sendo mais rápida com temperaturas mais elevadas. Este resultado reflectiou-se no rácio C/L obtendo-se 7,5 e 8,3 (130ºC), aumentando para 37,7 e 34,2 (150ºC), 44,3 e 41,3 (170ºC), respectivamente cerne e borne. Os valores de C/L estão relacionado com a perda de lenhina e de polissacáridos, i.e, para valores de C/L entre 5 e 10, correspodem a perdas de 60% de lenhina e 20-25% de polissacáridos. Posteriormente, a remoção de lenhina continuou mas a perda de polissacarideos manteve-se nos 30%, aumentando o rácio C/L. No final da deslenificação a 170ºC, as amostras foram caracterizadas com 2,3% e 2,2% (lenhina), 96,3% e 96,7% (polissacarideos) respectivamente cerne e borne. No geral não foram encontradas diferenças relativamente à deslenhificação do cerne comparativamente ao borne. No entanto foi evidente que durante a produção de pasta, os polissacarideos são removidos ao mesmo tempo que a lenhina, mas ao fim de algum tempo, a remoção de lenhina é maior, contribuindo para o aumento do rácio C/L.

Research paper thumbnail of Ozone Based TCF Bleaching of Non-wood Organosolv Pulps

... The overall bleaching results of organosolv pulps were superior to kraft. Full Text PDF (216k... more ... The overall bleaching results of organosolv pulps were superior to kraft. Full Text PDF (216kb). To cite this article: Shatalov, Anatoly A and Pereira, Helena. Ozone Based TCF Bleaching of Non-wood Organosolv Pulps [online]. ...

Research paper thumbnail of Importância dos fungos cromogéneos na fileira florestal. Avaliação preliminar da sua distribuição em Portugal

Resumo. O desenvolvimento de fungos cromogéneos representa o principal problema de degradação bio... more Resumo. O desenvolvimento de fungos cromogéneos representa o principal problema de degradação biológica para a madeira de pinheiro bravo (Pinus pinaster Ait.) recémabatida, causando fortes perdas na indústria de madeira em Portugal. Os fungos cromogéneos são os colonizadores primários, quer das células de parênquima radial quer das células lenhosas, e desenvolvem-se rapidamente no borne do pinho bravo iniciando o seu desenvolvimento, muitas vezes ainda na floresta, caso o processamento da madeira abatida não seja feito rapidamente. Com o presente estudo pretende-se contribuir para o conhecimento da distribuição destes fungos em Portugal continental, tendo para tal sido realizada uma campanha de amostragem em oito (8) serrações (Gerês, Vila Real, Viseu, Mangualde, Espinhal, Fazendas de Almeirim, Tavira e São Pedro do Sul) e efectuados isolamentos em meios artificiais a partir de madeira claramente infectada. Apresentam-se na presente comunicação os resultados preliminares desse estudo e discutese sumariamente o impacto dos fungos cromogéneos na actividade económica da fileira florestal.

Research paper thumbnail of Rapid Determination of the Lignin Content in Sitka Spruce (Picea sitchensis (Bong.) Carr.) Wood by Fourier Transform Infrared Spectrometry

Holzforschung, 1999

The rapid FTIR (Fourier transform infrared) spectroscopy technique was used to indirectly measure... more The rapid FTIR (Fourier transform infrared) spectroscopy technique was used to indirectly measure the lignin content of Sitka spruce wood samples. A model was constructed to relate FTIR data to lignin content measured in wood by chemical analysis (i.e. the modified acetyl bromide method), through the application of the principal component regression (PCR) approach to a set of calibration observations. The acetyl bromide method provided lignin determinations ranging from 24% to 34% with a measurement error of 0.6%. A residual standard deviation of 0.8% and an average prediction error of 0.9% were calculated for lignin content when employing the selected PCR model (based on a normalized infrared data set, obtained using the band at 1374 cm -1 as a reference) to indirectly measure this wood property. Furthermore, a large portion of the variability in lignin content was explained by the two principal components retained in the selected calibration model, as indicated by the magnitude (i.e. 0.93) of the coefficient of multiple determination. The model was subsequently employed to predict the lignin content of wood samples collected in a clonal experiment. Two multivariate diagnostic measures were applied to assess the quality of the individual predictions, and the results indicated that the spectral information contained in the new sample vectors was suitable for use with the selected calibration model.

Research paper thumbnail of Variability in the chemical composition of plantation eucalypts (Eucalyptus globulus Labill.)

Wood and Fiber Science, 1988

ABSTRACT The chemical composition was detcrmined for plantation-grown Eucalyptus globulus Labill.... more ABSTRACT The chemical composition was detcrmined for plantation-grown Eucalyptus globulus Labill., at time of harvest for pulpwood, with age 11-14 years, in four different locations and for the biomass com-ponents bolewood. bolcbark, tops, and branches. Chemical ...

Research paper thumbnail of La variation dans l'arbre de l'épaisseur du liége et du dos des planches de liége pour des chênes-liéges en pleine production

Research paper thumbnail of Influence of vision systems, black and white, colored and visual digitalization, in natural cork stopper quality estimation

Journal of the Science of Food and Agriculture, Jul 23, 2007

Quality classification of wine natural cork stoppers is related to presence of discontinuities in... more Quality classification of wine natural cork stoppers is related to presence of discontinuities in the cork tissue. Automated image analysis of stoppers based on black and white cameras is used industrially for commercial classification but recently color has been introduced in image processing. This paper compares the performance of three image vision systems regarding classification accuracy of cork stoppers of good, medium and inferior quality: black and white, three-band RGB color and manual detection by digitalization in color image. A canonical discriminant analysis approach was used to compare the discriminating power between cork stopper quality in each vision system. Good discriminant results were obtained with the area of pores expressed either in total or as ratio, mean or maximum value. The use of color slightly enlarges the range of cork inspection systems and automated systems have a similar accuracy of classification to visual inspection.

Research paper thumbnail of Comparison of Py-GC/FID and Wet Chemistry Analysis for Lignin Determination in Wood and Pulps from Eucalyptus globulus

Bioresources, Apr 30, 2013

The kraft pulps produced from heartwood and sapwood of Eucalyptus globulus at 130 ºC, 150 ºC, and... more The kraft pulps produced from heartwood and sapwood of Eucalyptus globulus at 130 ºC, 150 ºC, and 170 ºC were characterized by wet chemistry (total lignin as sum of Klason and soluble lignin fractions) and pyrolysis (total lignin denoted as py-lignin). The total lignin content obtained with both methods was similar. In the course of delignification, the py-lignin values were higher (by 2 to 5%) compared to Klason values, which is in line with the importance of soluble lignin for total lignin determination. Pyrolysis analysis presents advantages over wet chemical procedures, and it can be applied to wood and pulps to determine lignin contents at different stages of the delignification process. The py-lignin values were used for kinetic modelling of delignification, with very high predictive value and results similar to those of modelling using wet chemical determinations.

Research paper thumbnail of O montado e a cortiça. Livro de Resumos

A regeneração natural do sobreiro inicia-se com a germinação de plântulas, após a queda das bolot... more A regeneração natural do sobreiro inicia-se com a germinação de plântulas, após a queda das bolotas. Estas plântulas estabelecem-se, crescem e formam árvores que continuarão o ciclo da regeneração florindo, frutificando e produzindo novas bolotas. Ao longo deste processo vários factores podem limitar o recrutamento de jovens árvores. Apesar da produção de bolota variar entre árvores e anos, e as bolotas serem muito predadas e terem longevidade curta, a limitação do recrutamento não se deve, em geral, à escassez de sementes mas concentra-se nos dois primeiros anos de vida.

Research paper thumbnail of ¿Qué hay que tener en cuenta para elaborar modelos de producción de corcho?: revisión bibliográfica y consideraciones estadísticas

Research paper thumbnail of Modelo de crecimiento en diámetro para alcornocales del centro y sur de Portugal

Los modelos presentados son modelos de árbol individual en los que se analiza la influencia de la... more Los modelos presentados son modelos de árbol individual en los que se analiza la influencia de las dimensiones del individuo, la gestión aplicada en el descorche y la competencia intraespecífica en el crecimiento diametral. La variable independiente es el crecimiento medio en circunferencia bajo corcho calculado por diferencia de dos mediciones tomadas en intervalos de nueve o diez años. La estructura inicial del modelo es la de un modelo mixto con efectos fijo de intervalo de medición (9 o 10 años) y de región y efecto aleatorio de parcela. La variable dependiente que más variabilidad explica es la intensidad de descorche. El efecto regional es significativo a diferencia del efecto parcela, por lo que el modelo final seleccionado es un modelo de efectos fijos. El índice independiente de la distancia "Área de crecimiento proporcional al diámetro" es el de mejor comportamiento. Dentro de los dependientes de la distancia el de "Distancia ponderada por dimensiones" ...

Research paper thumbnail of Variation of lignin monomeric composition during kraft pulping of Eucalyptus globulus heartwood and sapwood

Journal of Wood Chemistry and Technology, 2012

Heartwood and sapwood samples from Eucalyptus globulus were characterized by Py-GC/MS and GC-FID ... more Heartwood and sapwood samples from Eucalyptus globulus were characterized by Py-GC/MS and GC-FID in respect to composition and content of lignin. The pyrolysis lignin-derived compounds were assembled by groups: “syringol,” “S-aldehydes,” “S-ketones,” “S-alcohols,” and “C11H12O3” (S-units); “guaiacol,” “eugenol,” “G-aldehydes,” “G-ketones,” “G-alcohols,” and “others” (G-units); “phenol” and “H-aldehydes” (H-units). Heartwood and sapwood had similar lignin content in an extractive-free basis (23.7% and 23.0%, respectively) and in lignin composition (S-units, 76.0% vs. 76.3%; G-units, 22.0% vs. 21.0%; H-units, 1.9% vs. 2.7%; S/G ratio 3.5 and 3.6). The wood samples were kraft pulped under isothermal conditions at 130°C, 150°C and 170°C and several cooking times. Heartwood and sapwood behaved similarly. At 130°C the delignification was slow with no significant selectivity in respect to lignin composition. At 150°C and 170°C the S-units were more susceptible to reaction and comparatively more removed, inducing a decrease of S/G ratio to 0.6. The main products to be extracted belong to “syringol” and “S-aldehydes,” while the residual lignin in pulps was enriched in “guaiacol,” “eugenol” (G-units), and “phenol” (H-units).

Research paper thumbnail of ANATOMICAL CHARACTERISATION AND VARIABILITY OF THE THISTLE CYNARA CARDUNCULUS IN VIEW OF PULPING POTENTIAL

The thistle Cynara cardunculus L. is an herbaceous perennial with high productivity that is harve... more The thistle Cynara cardunculus L. is an herbaceous perennial with high productivity that is harvested annually and is a potential fibre crop for paper pulp production. The anatomical variation within stalks was studied (base, middle and top) and compared in C. cardunculus plants at different development phases. The stalk of C. cardunculus includes an epidermis, cortex and a central cylinder with fibro-vascular bundles with phloem, xylem and a fibrous sheath that is variable in arrangement and size within and between plants. At harvest, the pith represents 37% of the stalk transectional area and 7% of the total weight. There was a slight variation in quantitative features of, respectively, the three development groups studied; mean fibre length was 1.04 mm, 0.95 mm and 1.05 mm; mean fibre width was 15 μm, 16 μm and 21 μm; mean fibre wall thickness was 3.2 μm, 3.4 μm and 4.9 μm. Fibre length and width decreased within the stem from base to top, while fibre wall thickness increased. Mean vessel diameter was 22 μm and mean vessel element length 220-483 μm. In mature plants, parenchyma represents 39% of the total transectional area and fibres 25%. The proportion of fibres increases during plant development and in mature plants is highest at the stalk base. As regards anatomical features, Cynara stalks compare favourably to other annual plants and fibre biometry indicates good potential for paper sheet forming and strength properties.

Research paper thumbnail of Reactivity of syringyl and guaiacyl lignin units and delignification kinetics in the kraft pulping of Eu-calyptus globulus wood using Py-GC-MS/FID.

Eucalyptus globulus sapwood and heartwood showed no differences in lignin content (23.0% vs. 23.7... more Eucalyptus globulus sapwood and heartwood showed no differences in lignin content (23.0% vs. 23.7%)
and composition: syringyl-lignin (17.9% vs. 18.0%) and guaiacyl-lignin (4.8% vs. 5.2%). Delignification kinetics of S- and G-units in heartwood and sapwood was investigated by Py-GC–MS/FID at 130, 150 and 170 ºC and modeled as double first-order reactions. Reactivity differences between S and G-units
were small during the main pulping phase and the higher reactivity of S over G units was better expressed in the later pulping stage. The residual lignin composition in pulps was different from wood or from samples in the initial delignification stages, with more G and H-units. S/G ratio ranged from 3 to 4.5 when pulp residual lignin was higher than 10%, decreasing rapidly to less than 1. The S/H was initially around 20 (until 15% residual lignin), decreasing to 4 when residual lignin was about 3%.

Research paper thumbnail of Evaluation of beech wood defects due to different drying schemes

Drying above the fiber saturation point is pure water transport without shrinkage. Shrinkage star... more Drying above the fiber saturation point is pure water transport without shrinkage. Shrinkage starts from moisture content below the fiber saturation point. This is motivated by the fact with development of strain and stress, occurs only that point. The paper presents the results obtained in an experimental study concerning the influence of drying temperature on beech wood (Fagus sylvatica L.).

Research paper thumbnail of Incork. Avaliação da influência da estrutura interna na transmissão de oxigénio de rolhas de cortiça natural por técnicas não destrutivas

A avaliação da qualidade das rolhas de cortiça natural é feita actualmente por uma análise visual... more A avaliação da qualidade das rolhas de cortiça natural é feita actualmente por uma análise visual da sua superfície exterior utilizando sistemas automáticos de análise de imagem ou operadores. As rolhas de boa qualidade apresentam poucos poros de pequena dimensão, contrariamente às de menor qualidade com muitos poros ou poros de grande dimensão. Verificase, no entanto, que existe uma grande heterogeneidade das classes de qualidade em relação à taxa de transmissão de oxigénio, uma importante propriedade das rolhas de cortiça, definidora da sua capacidade como vedante. Os estudos existentes têm mostrado que a transmissão de oxigénio das rolhas naturais é independente dos parâmetros clássicos de valorização comercial, classe visual de qualidade, diâmetro, comprimento e massa volúmica. Estes resultados evidenciam a necessidade de identificar parâmetros críticos internos à superfície da rolha, responsáveis por classes de qualidade não homogéneas. O projeto de investigação INCORK tem como principal objectivo o desenvolvimento de uma nova forma de caracterizar as rolhas de cortiça natural, usando não só as suas características externas, mas também as suas características internas. Para atingir este objectivo procedeu-se à caracterização total da estrutura interna e externa de rolhas de cortiça natural, efectuando uma caracterização por análise de imagem da superfície exterior, bem como aplicando técnicas não destrutivas de caracterização de materiais, nomeadamente radiação terahertz e tomografia axial computorizada (TAC). O INCORK visa o desenvolvimento de um novo sistema integrado de avaliação não destrutiva da estrutura interna e da superfície exterior das rolhas de cortiça que permita optimizar a sua classificação do ponto de vista da qualidade e de transmissão de oxigénio.

Research paper thumbnail of Tensile properties of cork in axial stress and influence of porosity, density, quality and radial position in the plank

European Journal of Wood and Wood Products, Feb 1, 2011

The behaviour of cork under tensile stress in the axial direction was studied for samples taken f... more The behaviour of cork under tensile stress in the axial direction was studied for samples taken from cork planks of good (class 1) and poor (class 4) quality grades and at three radial positions within the plank (inner, mid and outer positions). The effect of cork density (ranging from 0.123 to 0.203 g.cm -3 ) and porosity (ranging from 2.8 to 9.6% in the tangential surface) on Young's modulus and fracture stress and strain was studied. The tensile stress-strain curves of cork showed an elastic deformation up to 2% strain with a Young's modulus of 30.8 MPa, and a fracture stress of 1.05 MPa at a strain of 7.1% for class1, and Young's modulus of 26.1 MPa, and a fracture stress of 0.77 MPa at a strain of 5.5 % for class 4. Fracture always started at a pore. The quality class and the radial position in the plank were highly significant factors of the tensile properties variation with good quality cork in the inner part of the plank showing the highest strength. Density influenced the elastic behaviour of cork with a highly significant correlation of increasing E with density, but not so clearly the fracture stress and strain. The variability of tensile properties with porosity was large and although significant, the correlations were lower in spite of a decreasing trend of E with porosity. Fracture depended on the type of defects in cork.

Research paper thumbnail of Definition of quality classes for champagne cork stoppers in the high quality range

Wood Science and Technology, 2000

For champagne and other sparkling wines, agglomerated cork stoppers are used, lined at the bottom... more For champagne and other sparkling wines, agglomerated cork stoppers are used, lined at the bottom with two superposed discs of natural cork. The quality evaluation of champagne stoppers in the high quality range was made in relation to the porosity of the visible surface of the bottom cork disc using image analysis techniques. The average porosity coef®cient was 3.1%. Most pores were small but approx. 75% of the total porosity comes from pores with an area >0.25 mm 2 . Pores with a high visual impact (>2.0 mm 2 ) are less than 1% and were not determinant to the total porosity. The quality grading could be made using porosity coef®cients as selection criteria to discriminate between classes. In comparison to commercial grading, the use of quanti®ed porosity parameters for quality class de®nition allowed higher within class homogeneity and between class differentiation.

Research paper thumbnail of Tensile properties of cork in the tangential direction : variation with quality, porosity, density and radial position in the cork plank

The behaviour of cork under tensile stress in the tangential direction was evaluated in relation ... more The behaviour of cork under tensile stress in the tangential direction was evaluated in relation with its structural characteristics. The study was made using raw cork planks of two commercial quality classes (class 1, good quality and class 4, poor quality) collected at one industrial mill after post-harvest six-month air stabilization. Cork samples were taken at three radial positions in the cork planks (outer, mid and inner part). The porosity of the samples was determined by image analysis on the surfaces parallel to the tensile stress. The tensile test used a crosshead speed of 5 mm min -1 , corresponding to a strain rate of 1.7 x10 -3 s -1 . Young's modulus was calculated from the average slope of the stress-strain curve between the loads of 10 N and 100 N, corresponding to strains between approximately 1% and 2.5%. The cork samples presented densities ranging 0.129-0.186 g.cm -3 and porosities ranging 2.9-10.7%. There was no significant difference in the tensile properties of cork samples obtained from cork planks of different quality classes. However, the radial position in the cork plank was a highly significant factor of variation in the tensile tests, with higher strength for the cork samples taken in the inner part. The tensile properties (Young's modulus, fracture stress and fracture strain) showed a good correlation with cork density. The porosity had a good correlation, but in inverse order, only for the good quality (class1) cork planks.

Research paper thumbnail of Análise espacial da mortalidade do sobreiro em S. Bartolomeu da Serra (Santiago do Cacém)

Resumo. Avaliou-se a distribuição espacial da mortalidade do sobreiro (Quercus suber L.) na área ... more Resumo. Avaliou-se a distribuição espacial da mortalidade do sobreiro (Quercus suber L.) na área da freguesia de S. Bartolomeu da Serra (Santiago do Cacém), integrada numa região em que ela ocorre com elevada incidência, através de técnicas de detecção remota (SIG), e determinou-se a probabilidade de ocorrência de mortalidade através da aplicação de um modelo de regressão logística. Determinou-se um índice de mortalidade e identificaram-se as unidades fisiográficas com maior probabilidade de mortalidade em três sistemas agroflorestais distintos: floresta de sobreiro (florestas densas), montado de sobro tradicional (florestas abertas em sistemas dominantemente agrícolas, com culturas arvenses sob coberto) e incultos (florestas abertas em sistemas dominantemente incultos, com matos sob coberto). A mortalidade do sobreiro é significativamente diferente para os três tipos de sistemas agro-florestais. A mortalidade é influenciada por características físicas da paisagem como o solo, o declive e a exposição. Em solos pouco profundos ou em solos mais compactos, a mortalidade é mais frequente, mostrando a importância do desenvolvimento radicular em profundidade do sobreiro em regiões susceptíveis a extensos períodos de secura. Palavras-chave: Quercus suber L., declínio do montado de sobro, detecção remota regressão logística, mortalidade do sobreiro *** POSTERS TEMA 1 125

Research paper thumbnail of Caracterização por pirólise (Py-GC/MS(FID)) do cerne, borne e pastas kraft de eucalipto

A Eucalyptus globulus é uma espécie muito usada para a produção de pasta para papel devido às sua... more A Eucalyptus globulus é uma espécie muito usada para a produção de pasta para papel devido às suas caracteristicas químicas, em particular o conteúdo e composição da lenhina. Para este trabalho, o cerne e o borne do eucalipto foram caracterizados por pirólise (Py-GC/MS(FID)). O cerne e o borne apresentaram conteúdos semelhantes em lenhina (L) e polissacáridos (C) , respectivamente 23,7% e 74,5% (cerne), 23,0% e 74,5% (borne), resultando num rácio C/L de 3,1 e 3,2. Para estudar a deslenhificação foram produzidas pastas kraft a 130, 150 e 170 ºC, durante vários tempos de cozimento (de 1 a 185 min). O efeito da temperatura na deslenhificação foi evidente: a lenhina foi removida lentamente a 130 ºC, sendo mais rápida com temperaturas mais elevadas. Este resultado reflectiou-se no rácio C/L obtendo-se 7,5 e 8,3 (130ºC), aumentando para 37,7 e 34,2 (150ºC), 44,3 e 41,3 (170ºC), respectivamente cerne e borne. Os valores de C/L estão relacionado com a perda de lenhina e de polissacáridos, i.e, para valores de C/L entre 5 e 10, correspodem a perdas de 60% de lenhina e 20-25% de polissacáridos. Posteriormente, a remoção de lenhina continuou mas a perda de polissacarideos manteve-se nos 30%, aumentando o rácio C/L. No final da deslenificação a 170ºC, as amostras foram caracterizadas com 2,3% e 2,2% (lenhina), 96,3% e 96,7% (polissacarideos) respectivamente cerne e borne. No geral não foram encontradas diferenças relativamente à deslenhificação do cerne comparativamente ao borne. No entanto foi evidente que durante a produção de pasta, os polissacarideos são removidos ao mesmo tempo que a lenhina, mas ao fim de algum tempo, a remoção de lenhina é maior, contribuindo para o aumento do rácio C/L.

Research paper thumbnail of Ozone Based TCF Bleaching of Non-wood Organosolv Pulps

... The overall bleaching results of organosolv pulps were superior to kraft. Full Text PDF (216k... more ... The overall bleaching results of organosolv pulps were superior to kraft. Full Text PDF (216kb). To cite this article: Shatalov, Anatoly A and Pereira, Helena. Ozone Based TCF Bleaching of Non-wood Organosolv Pulps [online]. ...

Research paper thumbnail of Importância dos fungos cromogéneos na fileira florestal. Avaliação preliminar da sua distribuição em Portugal

Resumo. O desenvolvimento de fungos cromogéneos representa o principal problema de degradação bio... more Resumo. O desenvolvimento de fungos cromogéneos representa o principal problema de degradação biológica para a madeira de pinheiro bravo (Pinus pinaster Ait.) recémabatida, causando fortes perdas na indústria de madeira em Portugal. Os fungos cromogéneos são os colonizadores primários, quer das células de parênquima radial quer das células lenhosas, e desenvolvem-se rapidamente no borne do pinho bravo iniciando o seu desenvolvimento, muitas vezes ainda na floresta, caso o processamento da madeira abatida não seja feito rapidamente. Com o presente estudo pretende-se contribuir para o conhecimento da distribuição destes fungos em Portugal continental, tendo para tal sido realizada uma campanha de amostragem em oito (8) serrações (Gerês, Vila Real, Viseu, Mangualde, Espinhal, Fazendas de Almeirim, Tavira e São Pedro do Sul) e efectuados isolamentos em meios artificiais a partir de madeira claramente infectada. Apresentam-se na presente comunicação os resultados preliminares desse estudo e discutese sumariamente o impacto dos fungos cromogéneos na actividade económica da fileira florestal.

Research paper thumbnail of Rapid Determination of the Lignin Content in Sitka Spruce (Picea sitchensis (Bong.) Carr.) Wood by Fourier Transform Infrared Spectrometry

Holzforschung, 1999

The rapid FTIR (Fourier transform infrared) spectroscopy technique was used to indirectly measure... more The rapid FTIR (Fourier transform infrared) spectroscopy technique was used to indirectly measure the lignin content of Sitka spruce wood samples. A model was constructed to relate FTIR data to lignin content measured in wood by chemical analysis (i.e. the modified acetyl bromide method), through the application of the principal component regression (PCR) approach to a set of calibration observations. The acetyl bromide method provided lignin determinations ranging from 24% to 34% with a measurement error of 0.6%. A residual standard deviation of 0.8% and an average prediction error of 0.9% were calculated for lignin content when employing the selected PCR model (based on a normalized infrared data set, obtained using the band at 1374 cm -1 as a reference) to indirectly measure this wood property. Furthermore, a large portion of the variability in lignin content was explained by the two principal components retained in the selected calibration model, as indicated by the magnitude (i.e. 0.93) of the coefficient of multiple determination. The model was subsequently employed to predict the lignin content of wood samples collected in a clonal experiment. Two multivariate diagnostic measures were applied to assess the quality of the individual predictions, and the results indicated that the spectral information contained in the new sample vectors was suitable for use with the selected calibration model.

Research paper thumbnail of Variability in the chemical composition of plantation eucalypts (Eucalyptus globulus Labill.)

Wood and Fiber Science, 1988

ABSTRACT The chemical composition was detcrmined for plantation-grown Eucalyptus globulus Labill.... more ABSTRACT The chemical composition was detcrmined for plantation-grown Eucalyptus globulus Labill., at time of harvest for pulpwood, with age 11-14 years, in four different locations and for the biomass com-ponents bolewood. bolcbark, tops, and branches. Chemical ...

Research paper thumbnail of La variation dans l'arbre de l'épaisseur du liége et du dos des planches de liége pour des chênes-liéges en pleine production

Research paper thumbnail of Influence of vision systems, black and white, colored and visual digitalization, in natural cork stopper quality estimation

Journal of the Science of Food and Agriculture, Jul 23, 2007

Quality classification of wine natural cork stoppers is related to presence of discontinuities in... more Quality classification of wine natural cork stoppers is related to presence of discontinuities in the cork tissue. Automated image analysis of stoppers based on black and white cameras is used industrially for commercial classification but recently color has been introduced in image processing. This paper compares the performance of three image vision systems regarding classification accuracy of cork stoppers of good, medium and inferior quality: black and white, three-band RGB color and manual detection by digitalization in color image. A canonical discriminant analysis approach was used to compare the discriminating power between cork stopper quality in each vision system. Good discriminant results were obtained with the area of pores expressed either in total or as ratio, mean or maximum value. The use of color slightly enlarges the range of cork inspection systems and automated systems have a similar accuracy of classification to visual inspection.

Research paper thumbnail of Comparison of Py-GC/FID and Wet Chemistry Analysis for Lignin Determination in Wood and Pulps from Eucalyptus globulus

Bioresources, Apr 30, 2013

The kraft pulps produced from heartwood and sapwood of Eucalyptus globulus at 130 ºC, 150 ºC, and... more The kraft pulps produced from heartwood and sapwood of Eucalyptus globulus at 130 ºC, 150 ºC, and 170 ºC were characterized by wet chemistry (total lignin as sum of Klason and soluble lignin fractions) and pyrolysis (total lignin denoted as py-lignin). The total lignin content obtained with both methods was similar. In the course of delignification, the py-lignin values were higher (by 2 to 5%) compared to Klason values, which is in line with the importance of soluble lignin for total lignin determination. Pyrolysis analysis presents advantages over wet chemical procedures, and it can be applied to wood and pulps to determine lignin contents at different stages of the delignification process. The py-lignin values were used for kinetic modelling of delignification, with very high predictive value and results similar to those of modelling using wet chemical determinations.