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Com o presente trabalho pretende-se aprofundar o conhecimento sobre o potencial papeleiro da madeira de Acacia melanoxylon e Acacia dealbata. Para efeitos de posicionamento relativo das matérias primas, utilizaram-se aparas industriais de Eucalyptus globulus. A transformação da madeira em pasta foi realizada através do processo ao sulfato. O comportamento global das três espécies nos processos de cozimento e branqueamento é semelhante. No entanto, face à amostra de Eucalyptus globulus usada, a Acacia melanoxylon exibe um rendimento em pasta ligeiramente superior, o que está de acordo com os teores de lenhina e extractivos das madeiras. Para avaliar o potencial das pastas branqueadas na produção de papel, estas foram submetidas ao processo de refinação, em PFI, tendo-se obtido suspensões de pastas com resistência à drenagem crescentes. Posteriormente, caracterizou-se a suspensão fibrosa e o potencial papeleiro. Para o mesmo nível de refinação, os papéis produzidos com fibras de acácia apresentam valores superiores de lisura, índice de tracção e índice de rebentamento. Por outro lado, as fibras da Eucalyptus globulus apresentam maior resistência intrínseca e têm potencial para produzir papeis mais resistentes, embora à custa de maior consumo de energia na refinação. Para um dado nível de resistência mecânica, as características ópticas dos papéis são semelhantes.

Este estudo analisa o efeito do teor de hemiceluloses das pastas de eucalipto nas características do papel produzido. Para o efeito, utilizaram-se aparas industriais de Eucalyptus globulus, com massa volúmica básica de 536 ± 4 kg/m3. As aparas crivadas foram sujeitas ao processo kraft, convencional e modificado, para a produção das respectivas pastas cruas com teores de hemiceluloses diferentes. Os cozimentos realizaram-se num digestor descontínuo de circulação forçada, com 1000g de madeira. A pasta crua foi submetida a um branqueamento ECF com dióxido de cloro, segundo uma sequência de cinco estágios (D0E1D1E2D2). As duas pastas, convencional e modificada, apresentaram teores de hemiceluloses da ordem dos 19% e 14%, respectivamente. Posteriormente, a pasta branca foi caracterizada em termos biométricos e papeleiro. Para este fim, a pasta foi refinada em PFI (ISO 5264/2-79) a diversas revoluções e com uma carga específica de bordo de 2 Nmm-1, tendo-se contabilizado o consumo de energia. Caracterizou¬-se a suspensão fibrosa e o potencial papeleiro. Para um dado número de revoluções em PFI, a resistência à drenagem, a densidade e a resistência à tracção das folhas aumentam com o incremento do teor de hemiceluloses. Assim, para produzir papéis com a mesma densidade, as pastas com menor teor de hemiceluloses requerem mais energia de refinação.

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Este estudo analisa o efeito do teor de hemiceluloses das pastas de eucalipto nas características do papel produzido. Para o efeito, utilizaram-se aparas industriais de Eucalyptus globulus, com massa volúmica básica de 536 ± 4 kg/m3. As aparas crivadas foram sujeitas ao processo kraft, convencional e modificado, para a produção das respectivas pastas cruas com teores de hemiceluloses diferentes. Os cozimentos realizaram-se num digestor descontínuo de circulação forçada, com 1000g de madeira. A pasta crua foi submetida a um branqueamento ECF com dióxido de cloro, segundo uma sequência de cinco estágios (D0E1D1E2D2). As duas pastas, convencional e modificada, apresentaram teores de hemiceluloses da ordem dos 19% e 14%, respectivamente. Posteriormente, a pasta branca foi caracterizada em termos biométricos e papeleiro. Para este fim, a pasta foi refinada em PFI (ISO 5264/2-79) a diversas revoluções e com uma carga específica de bordo de 2 Nmm-1, tendo-se contabilizado o consumo de energia. Caracterizou-se a suspensão fibrosa e o potencial papeleiro. Para um dado número de revoluções em PFI, a resistência à drenagem, a densidade e a resistência à tracção das folhas aumentam com o incremento do teor de hemiceluloses. Assim, para produzir papéis com a mesma densidade, as pastas com menor teor de hemiceluloses requerem mais energia de refinação.

We measured fibre morphological properties and corresponding handsheet paper properties in pulps obtained from Eucalyptus globulus, Acacia dealbata and Acacia melanoxylon wood samples. The three wood samples were chipped, cooked, and bleached according to standard procedures. The basic chip densities of the samples obtained from the three species studied were 0.351g/cm3, 0.387g/cm3 and 0.536g/cm3, respectively for A. dealbata, A. melanoxylon and E. globulus. All species were submitted to cooking with the following reaction conditions: active alkali charge = 22% (as NaOH); sulfidity index = 30%; liquor/wood ratio = 4/1; time to temperature = 90 min; time at temperature (160 ºC) = 120 min. Acacia species show higher pulp yield than the E. globulus sample used as a reference and cooking selectivity is higher in the Acacia species investigated. The three pulps were beaten in a PFI mill at 500, 2500 and 4500 revolutions under a refining intensity of 3.33 N/mm, and laboratory paper sheets were produced, including the unbeaten pulps, which made up 4 samples per species. The corresponding fibre characteristics in suspension were also determined. We used principal components analysis to investigate the differences in fibre characteristics and paper properties, as well as their interaction. Each value of these variables represents a mean of 10 tests, for the paper sheets. This methodology allowed us to determine how close, or how independent, the study variables were. We conclude there is a group of paper characteristics which depend strongly on each other - paper density, smoothness, tensile index, stretch, burst index, Schopper Riegler degree, internal cohesion and WRV – and are negatively correlated with the light scattering coefficient, opacity and brightness. On the other hand, intrinsic paper fibre resistance is strongly affected by fibre length and coarseness. On the basis of the properties we studied, it is clear that paper produced from Eucalyptus fibre has different properties from that produced from Acacia fibre. Papers produced from both species of Acacia are similar.

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Relation between wood density and paper properties of some hardwood species.

Wood density is a complex physical property related to the anatomical structure and the chemical composition of wood and one of the most important wood quality factors. Sampling was based on a total of 20 trees from four sites in Portugal that were harvested at a sawmill diameter class of 40 cm and wood discs taken at different height levels from the base to the top of the tree. The mean basic density of the Acacia melanoxylon trees measured at 5% height level (near breast height level) was 516 kg/m3 with a 34 kg/m3 standard deviation. The within-tree axial variation of density was of small magnitude, but showing higher values at the stem base and top. Site had no influence on the basic density of the wood. Overall the between tree variation of density was small possibly linked to the narrow genetic diversity of this introduced exotic species. In the Kraft process we can observe variability between stands and an increase of the pulp yield, and fiber width and length with the higher level in the tree. The wood basic density is well correlated with the ISO brightness and well correlated in inverse order with the pulp Yield and fiber width and length. The kappa number don’t present a great variation with the wood basic density.

This paper reports experimental data about wood chemical composition (extractives and lignin content), fibre characteristics, kraft cooking behaviour and papermaking potential of two wood samples of Eucalyptus globulus (one industrial chip sample and another obtained from a clone tree). The samples were submitted to the kraft cooking and bleaching processes in order to evaluate its pulping potential. The experimental results showed that the clone tree requires milder cooking conditions and exhibits higher pulp yield. The pulp fibres obtained from the clone have higher fibre length and fibre width and lower coarseness, which give higher fibre flexibility and collapsibility. In consequence, structural, mechanical and optical properties of paper are significantly different. In addition, we observed that the fibres from the clone tree are weaker than the corresponding fibres from the industrial sample.

The raw-material composition and the cooking conditions determine the pulp composition and this affect the behaviour of the pulp in the beating process and the papermaking potential. However, at industrial scale the variability of the pulp composition, for a given raw material and a given process, is relatively low and usually it is difficult to quantify the impacts of pulp composition on beating and papermaking. In the present study E. globulus bleached pulps were produced under different cooking conditions by the kraft process in order to obtain pulps with significant different hemicelluloses content (19% versus 14.5%). The behaviour of the pulps in beating and the papermaking potential were investigated under two beating intensities in the PFI mill and at four beating times. The pulp suspensions were characterised in terms of drainability, fibre morphology, wet fibre flexibility and relative bonded area. The paper produced was evaluated in terms of structural, superficial, mechanical and optical properties. The results showed the clear effect of the hemicelluloses content on the beating rate as well as on the paper properties.

The pulping and papermaking potential of Acacia dealbata and Acacia melanoxylon were studied using Eucalyptus globulus as a reference. Pulp yield, alkali consumption and delignification in the kraft process, of both species, compare very well with the reference. Pulp yield can be higher than that of E. globulus and the residual lignin content lower after cooking, which is in good agreement with the lower lignin and extractives content of the wood samples used. Pulps produced from Acacia have slightly lower fibre length and coarseness and higher fibre width and wet fibre flexibility than E. globulus pulps. As a consequence of fibre characteristics, the paper produced from Acacia is denser and exhibits higher tensile and burst strength, and lower tear resistance than that from E. globulus, at a given PFI revolution.

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.

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No presente trabalho estudou-se o comportamento de três amostras de madeira de Eucalyptus globulus nacional, com massas volúmicas básicas entre 467 kg/m3 e 600 kg/m3, no processo de cozimento kraft e analisou-se as características biométricas do material fibroso. As matérias primas em estudo apresentam rendimentos em pasta entre 49 e 59% e as fibras exibem dimensões muito diferentes. O valor médio da espessura de parede das fibras variou entre 2.5 e 3.5 μm, respectivamente para a madeira de massa volúmica básica 467kg/m3 e 600 kg/m3. A largura das fibras varia de forma muito menos acentuada. Em consequência, as fibras de parede fina exibem elevadas flexibilidade e colapsibilidade em estado húmido, enquanto que as de maior espessura de parede são muito mais rígidas. O efeito da refinação sobre estas propriedades é igualmente diferente. As características biométricas reflectem-se de forma muito acentuada na necessidade de refinação e nas características do papel.

Refining is an important unit operation in the paper production process and consists in the mechanical beating of the pulp fibres in an aqueous medium. The refining conditions affect fibre morphology, pulp suspension characteristics and paper properties. In this study we investigated the effect of refining intensity - given by the specific edge load (SEL) - on the fibre and paper properties. Lower refining intensity led to lower fibre cutting, lower fines generation, and lower ºSR development. Commercial Eucalyptus globulus bleached pulp was refined in a pilot refiner, using different specific edge loads (0.05; 0.1 and 0.2 J/m) and specific energy consumption of 40, 80 and 120 kWh/ton in order to evaluate paper potential. The highest specific edge load tested (0,2 J/m) resulted in a lower average fibre length, as a result of a higher fibre cutting. The papers produced presented higher mechanical resistance, but increasing refinement energy from 80 to 120 kWh/ton did not improve paper properties. On the contrary, with a lowest specific edge load (0,05 J/m), the papers obtained for different specific energy consumption exhibited lower density (i.e., higher open structure, higher air permeability and lower smoothness).

Potential of cypress wood for pulp production.

In this work we study the behaviour in kraft cooking and papermaking of 6 Acacia melanoxylon wood chip samples, with basic densities of 449, 489, 493, 505, 514 and 616 kg/m3. The wood chip samples were screened and submitted to the kraft cooking process. Experiments were carried out with 1000-g o.d. of wood in a forced circulation digester. The cooked chips were disintegrated, screened and washed. The screened and total yields, kappa number and pulp viscosity were determined according to the standard methods. The morphological properties of pulp fibres were determined by image analysis of a diluted suspension in a flow chamber in Morfi®. The unbleached kraft pulps were submitted to a bleaching D0E1D1E2D2 sequence and their papermaking potential evaluated. The pulps were beaten in a PFI mill at 500, 2500 and 4500 revolutions under a refining intensity of 1.7 N/mm. Paper handsheets were prepared according to the Scan standard and tested regarding structural, mechanical and optical properties. Regarding the pulping potential, the pulp yield ranged between 47.7 and 57.7%. The selected wood samples provided bleached kraft pulps with markedly different biometrics characteristics. In fact, the mean values of fibre length, fibre width and coarseness ranged between 0.77 and 0.98 mm, 17.8 and 19.4 μm, 4.8 and 6.2 mg/100m, respectively. As expected, these biometrics characteristics have very high impact on paper structure, including smoothness, and on mechanical and optical properties, for the unbeaten pulps. At a given beaten level, the differences between pulps remain very high. Moreover, for a given paper density, tensile and tear strength, and light scattering coefficient are significantly different. To reach a given paper density, however, the different pulps required very different energy consumptions in beating.

A total of 120 Acacia melanoxylon R. Br. (Australian blackwood) stem discs, belonging to 20 trees from four sites in Portugal, were used in this study. The samples were kraft pulped under standard identical conditions targeted to a Kappa number of 15. A Near Infrared (NIR) partial least squares regression (PLSR) model was developed for the Kappa number prediction using 75 pulp samples with a narrow Kappa number variation range of 10 to 17. Very good correlations between NIR spectra of A. melanoxylon pulps and Kappa numbers were obtained. Besides the raw spectra, also pre-processed spectra with ten methods were used for PLS analysis (cross validation with 48 samples), and a test set validation was made with 27 samples. The first derivative spectra in the wavenumber range from 6110 to 5440 cm-1 yielded the best model with a root mean square error of prediction of 0.4 units of Kappa number, a coefficient of determination of 92.1%, and two PLS components, with the ratios of performance to deviation (RPD) of 3.6 and zero outliers. The obtained NIR-PLSR model for Kappa number determination is sufficiently accurate to be used in screening programs and in quality control.

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A Acacia melanoxylon R. Br. (acácia-austrália ou austrália) cresce bem em Portugal, em povoamentos puros ou mistos com Pinus pinaster Aiton, ainda que apresente fortes constrangimentos ecológicos e legais. Apesar de algumas dificuldades, por exemplo na secagem, a madeira de austrália é usada em mobiliário e produtos manufacturados devido, principalmente, à sua textura e cor escura. Pode também ser usada para pasta, sendo plantada em muitos países com esse propósito juntamente com Acacia mangium e A. dealbata. O seu potencial papeleiro tem sido estudado por vários autores (CLARK et al., 1991; GUIGAN et al., 1991; FURTADO, 1994; GIL et al., 1999; PAAVILAINEN, 2000; SANTOS et al., 2002; SANTOS et al., 2006). A indústria florestal em Portugal depende fortemente do pinheiro-bravo e do eucalipto, com a consequente competição negativa, entre as várias indústrias, para a mesma matéria-prima. Em Portugal existem muitos povoamentos espontâneos com acácia, nomeadamente A. dealbata e A. melanoxylon. Enquanto a A. dealbata é considerada um problema ecológico, a A. melanoxylon não o é e está bem adaptada às condições portuguesas. Por este motivo poderá ser considerada uma espécie produtora de matéria-prima alternativa das serrações e da indústria papeleira, e poderá evitar largas áreas de monocultura e minimizar o risco de incêndio. O acréscimo anual em diâmetro da acácia (0,89 cm.ano-1) excede o do pinheiro-bravo (0,58 a 0,85 cm.ano-1) (TAVARES et al., 2004) e aproxima-se do eucalipto (0,84 a 0,96 cm.ano-1) (TOMÉ et al., 2001). As propriedades da madeira sólida de acácia (Massa volúmica média - 650 kg.m-3 ± 75, Tensão média de rotura à flexão ± sd - 146 N.mm-2 ± 24, Módulo de elasticidade médio ± sd - 14200 N.mm-2 ± 2160 e Tensão média de rotura à compressão axial ± sd - 61 N.mm-2 ± 7) permitem considerá-la uma espécie alternativa ao pinheiro-bravo (630 kg.m-3 ± 75, 130 N.mm-2 ± 33, 10500 N.mm-2 ± 3590 e 47 N.mm-2 ± 10) (MACHADO e CRUZ, 2005). As madeiras de pinheiro-bravo e de acácia podem ser, em geral, classificadas como de fraca a média densidade, de média resistência e rigidez. A qualidade do pinho é muito variável, sendo o seu potencial reconhecido a partir de dados provenientes de povoamentos de elevada qualidade (MACHADO e CRUZ, 2005). Relativamente ao potencial papeleiro, para uma dada resistência à drenagem (30 ºSR), os papeis produzidos a partir de acácia apresentam densidades aparentes mais elevadas que as de eucalipto (0,80 to 0,66 g/cm3) (SANTOS et al., 2004). Isto é devido à menor massa linear e mais elevada flexibilidade e colapsabilidade das suas fibras (SANTOS et al., 2006). Apesar do ligeiramente maior comprimento de fibra, esta produz papeis com boa relação entre a dispersão de luz e a lisura, ainda com boa resistência à tracção e a baixos níveis de consumo de energia na refinação. Este comportamento demonstra que as fibras de acácia apresentam um potencial de utilização interessante, pelo menos quando usadas juntamente com fibras de eucalipto na produção de papel para impressão e escrita. Este artigo diz respeito à análise do potencial da acácia como fonte de matéria-prima para a indústria Portuguesa (como madeira sólida e pasta e papel), reunindo informação da gestão florestal, da qualidade da madeira e da fibra. Será usado conhecimento adquirido em projectos de investigação anteriores e resultados preliminares da investigação em curso sobre A. melanoxylon proveniente de povoamento mistos (com P. pinaster) e puros, no norte de Portugal.

In this paper we report new data about two wood species that could play a role in the Portuguese forest as raw material for the paper industry: Cupressus arizonica and Cupressus sempervirens. Results on the behaviour of wood samples taken from 16 year-old trees, (two per species and two height levels), have shown lower kraft pulp yields than reference pine softwoods, as a consequence of higher lignin content. The pulps from C. sempervirens present values of fibre lenght and coarseness slightly lower than the Nordic Pinus sylvestris, but properties of pulp fibres from C. arizonica are significantly lower.

DOI 10.1007/s10086-012-1286-2

Wood 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

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Most of the fibre raw materials used by the pulp and paper industry are from a small number of tree species. For instance, Eucalyptus and Pinus species are the major industrial pulpwood sources obtained from forests characterized by a relatively low biodiversity. The large monoculture areas also increase environmental risks such as those related to biotic attacks or forest fires. Diversification of industrial fibre sources has therefore been a matter of research and the characterization of different raw materials has been made in view of their pulping potential. Acacia melanoxylon R. Br. (blackwood) grows well in Portugal in pure or mixed stands with Pinus pinaster Aiton, and is valued as a timber species with potential for sawmills. In addition, the wood anatomical and chemical characteristics also allow to consider the species as an alternative raw material for the pulp industry. Acacia species, with their relatively short, flexible and collapsible fibres, have potential to produce papers with good trade-offs between light scattering/tensile strength and smoothness/tensile strength, at low energy consumption in refining. The pulping and paper making potential of blackwood has been studied by several authors showing an overall good pulping aptitude under the same experimental conditions of kraft pulping as used for eucalypt pulping with pulp yields ranging between 47 and 58 %. The presence of heartwood should be taken into account because it decreases the raw-material quality for pulping due to the higher extractives content. Heartwood proportion should therefore be considered as a quality variable when using A. melanoxylon wood in pulp industries. This chapter describes the characterization of the A. melanoxylon wood pulping performance, regarding yield and kappa number, and the pulp and paper properties. The application of fast spectroscopic technologies for pulp quality determination is also described.

Neste trabalho desenvolveu-se um modelo para estimar a densidade básica na madeira da Acacia melanoxylon po NIR.

Paper properties determine the product application potential and depend on the raw material, pulping conditions,and pulp refining. The aim of this study was to construct mathematical models that predict quantitative relations between the paper density and various mechanical and optical properties of the paper. A dataset of properties of paper handsheets produced with pulps of Acacia dealbata, Acacia melanoxylon, and Eucalyptus globullus beaten at 500, 2500, and 4500 revolutions was used. Unsupervised classification techniques were combined to assess the need to perform separated prediction models for each species, and multivariable regression techniques were used to establish such prediction models. It was possible to develop models with a high goodness of fit using paper density as the independent variable (or predictor) for all variables except tear index and zero-span tensile strength, both dry and wet.

Prediction paper properties based on a limited number of measured variables can be an important tool for the industry. Mathematical models were developed to predict mechanical and optical properties from the corresponding paper density for some softwood papers using support vector machine regression with the Radial Basis Function Kemel. A dataset of different properties of paper handsheets produced from pulps of pine (Pinus pinaster and P. sylvestris) and cypress species (Cupressus lusitanica, C. sempervirens e C. arizonica) beaten at 1000, 4000, and 7000 revolutions was used. The results show that it is possible to obtain good models (with high coefficient of determination) with two variables: the numerical variable density and the categorical variable density.

Paper properties determine the product application potential and depend on the raw material, pulping conditions, and pulp refining. The aim of this study was to construct mathematical models that predict quantitative relations between the paper density and various mechanical and optical properties of the paper. A dataset of properties of paper handsheets produced with pulps of Acacia dealbata, Acacia melanoxylon, and Eucalyptus globulus beaten at 500, 2500, and 4500 revolutions was used. Unsupervised classification techniques were combined to assess the need to perform separated prediction models for each species, and multivariable regression techniques were used to establish such prediction models. It was possible to develop models with a high goodness of fit using paper density as the independent variable (or predictor) for all variables except tear index and zero-span tensile strength, both dry and wet.

O 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.