Scielo RSS <![CDATA[Maderas. Ciencia y tecnología]]> vol. 13 num. 2 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<strong>Effectiveness of selected preservatives in protecting Ugandan grown <i>Eucalyptus grandis</i> wood against termite attack</strong>]]> Termites are one of the major wood destroying agents in the tropics and with the increasing rate of deforestation, there is a need to protect wood from biodegradation in order to extend its service life. In this study the incidence and severity of termite attack on Eucalyptus grandis sapwood treated with CCA, used engine oil and neem extract were investigated. Sixty samples (20 × 20 × 300mm) were prepared from the sapwood at mid-height of the tree of E. grandis and air seasoned for two weeks then treated with the preservatives. An area of 20m by 20m in a pine plantation and 15 plots of 1m by 1m were selected at random. Four samples, one from each treatment, were placed at the corners of the selected plots. Inspection and evaluation of stakes was made by visual assessments after every 30 days for any sign of termite attack for a period of 8 months. The specimens were removed from the ground, damage assessed and returned to the ground. After 4 weeks all the untreated wood samples had been attacked, neem extract treated wood samples were attacked after 17 weeks and used engine oil treated samples after 30 weeks. None of the CCA treated wood samples were attacked by the end of study period. Chi square analysis showed a high association between treatment and incidence as well as between treatment and severity. It was recommended that further research be carried out on neem extract using different concentrations. <![CDATA[<strong>Evaluating vibrations on a small-scale model of a timber footbridge</strong>]]> In Brazil, the study of pedestrian-induced vibration on footbridges has been undertaken since the early 1990s, for concrete and steel footbridges. However, there are no recorded studies of this kind for timber footbridges. Brazilian code ABNT NBR 7190 (1997) gives design requirements only for static loads in the case of timber footbridges, without considering the serviceability limit state from pedestrian-induced vibrations. The aim of this work is to perform a theoretical dynamic, numerical and experimental analysis on simply-supported timber footbridges, by using a small-scale model developed from a 24 m span and 2 m width timber footbridge, with two main timber beams. Span and width were scaled down (1:4) to 6 m e 0.5 m, respectively. Among the conclusions reached herein, it is emphasized that the Euler-Bernoulli beam theory is suitable for calculating the vertical and lateral first natural frequencies in simply-supported timber footbridges; however, special attention should be given to the evaluation of lateral bending stiffness, as it leads to conservative values. <![CDATA[<strong>Fibre level modelling of free water behaviour during wood drying and wetting</strong>]]> Most drying simulation models describe the moisture migration in wood as a diffusion process, including free water flow at contents greater than the fibre saturation point. This means that wood is seen as a homogeneous material lacking internal structure. However, especially in softwood narrow sections, bordered pits, divide the free water phase into rather distinct units. It is thus quite clear that the flow of free water is governed by capillary forces and not by diffusion. A model has been developed that investigates how water filled units are emptied one by one in a drying process. Simulations with the model explain some experimentally seen features that cannot be obtained using solely diffusion type models. Water absorption by dried wood is generally assumed to be governed by capillary (surface tension) forces. An additional feature is that a considerable part of the bordered pits have been aspirated, i.e. closed, in the drying process and the number of possible flow paths is thus reduced. Thus the driving force for water flow is the capillary suction into the lumen. Modelling wood wetting by these principles also introduces some interesting specific features, such as a limit regarding the maximal achievable water saturation. In summary it is found that specific behaviour seen on a real macroscopic level originates from properties at the microscopic, fibre level. This clearly indicates that experience from fibre level models should be included in future drying and wetting simulation models. The work in this direction so far, has been promising. <![CDATA[<strong>Mass transfer in medium density fiberboard (MDF) modified by Na<sup>+</sup> montmorillonite (Na<sup>+</sup>MMT) nanoclay</strong>]]> The potential use of nanoclay was examined to modify fluid transfer properties of medium density fiberboard (MDF). For this, Na+ montmorillonite (Na+MMT) nanoclay was added to urea formaldehyde resin to produce MDF. Then, the air permeability and mass diffusivity of MDF were evaluated. Scanning electron microscope (SEM) images and X-ray diffraction (XRD) confirmed a dispersion and exfoliation of Na+MMT in the modified MDF. The air permeability presented a systematic decrease with increasing nanoclay amount. This reduction agreed with the simple ‘‘tortuous path’’ model. The nanoclay had no effect on the mass diffusivity. <![CDATA[<strong>Inclusion of the sorption hysteresis phenomenon in future drying models</strong>: <strong>Some basic considerations</strong>]]> The sorption hysteresis effect, i.e. different wood equilibrium moisture contents (EMCs) in desorption and adsorption for the same relative humidity, is well known. However, quantitative sorption isotherms, in the form of tables or analytical correlations, are almost always given as the average of the desorption and adsorption curves. Consequently most drying simulation models use these average curves, and does not take into account the sorption hysteresis phenomenon. The equilibrium state of a wood sample is thus not a function of the relative humidity only, but depends on the moisture history also. This means that Fick's equations - with moisture content as a single driving force - are not valid any more. For a pure desorption process the state of the sample follows the desorption isotherm, but a problem arises when desorption is followed by adsorption - as for instance in the timber conditioning phase. It seems reasonable to assume that for each EMC point, on or between the desorption/adsorption isotherms, the moisture content change follows a unique path when the surrounding climate changes. This path - the so called scanning curve - does not need to be the same in desorption and adsorption. Some selected results and corresponding scanning curve suggestions are presented and discussed. Drying models with the sorption hysteresis phenomenon included should be developed for the analysis of experimental data and more generally for use as an improved tool in practical applications. <![CDATA[<strong>Wettability study and surface characterizacion by confocal laser scanning microscopy of rotary-peeled wood veneers</strong>]]> El objetivo de este trabajo fue estudiar las propiedades superficiales de chapas obtenidas por desenrollo de cinco especies de maderas duras: okume, ayous, chopo, fromager y eucalipto, y comparar el comportamiento de ambas caras de las chapas. Se han determinado los ángulos de contacto de equilibrio y se ha determinado la energía libre superficial de la madera así como sus componentes polar y dispersa. Asimismo, mediante microscopía de barrido láser confocal se ha evaluado la rugosidad superficial. La energía libre superficial osciló entre 49-64 mJ/m² y disminuyó en el orden okume > fromager > chopo > ayous ~ eucalipto, lo que indica un descenso de la capacidad de mojado en ese orden. El okume con el mayor valor de la energía libre superficial y los menores valores del ángulo de contacto de equilibrio se confirmó como la especie con las mejores propiedades de mojado, siendo además la que presentó los mayores valores de los parámetros de rugosidad superficial. Comparando las propiedades superficiales para las dos caras de las chapas se encontró que dependieron de la especie pero, en general, con la excepción de la rugosidad, las diferencias no fueron muy significativas siendo los mayores cambios para las chapas de okume que presentaron un mejor mojado en su cara interior.<hr/>The aim of this work was to study the surface properties of rotary-peeled veneers of five species of hardwoods: okume, ayous, poplar, fromager and eucalyptus and to compare the behavior of both sides of the veneers. The equilibrium contact angles were determined together with the wood surface free energy and its polar and disperse components. Additionally, surface roughness was evaluated using confocal laser scanning microscopy. Surface free energy ranged from 49-64 mJ/m² and decreased in the order okume> fromager> poplar> eucalyptus ~ ayous, indicating a decrease in wettability in that order. Okume wood with the highest value of the surface free energy and the lowest values of the equilibrium contact angle was confirmed as the species with the best wetting properties, and also presented the highest values of surface roughness parameters. In general, there were not significant differences between the properties of both sides of the veneers, except for roughness. The largest differences were obtained for okume veneers whose interior side showed higher wettability. <![CDATA[<strong>Influences of the operating variables of acetosolv pulping on pulp properties of oil palm frond fibres</strong>]]> The effect of acetosolv pulping variables viz. pulping time, temperature, catalyst (HCl) and acetic acid on oil palm frond fibres was investigated. The following conditions were found to be optimum to pulp frond fibres: 140 ºC, 0.5% HCl, 75% acetic acid, and 1/10 solid/liquor ratio. Under these conditions we could obtain these properties: Kappa number 13-16, zero-span tensile breaking length - 83 km, sheet density - 0.57 g cm-3, tensile index - 48 N m g-1, tear index - 5.4 mN m² g-1, brightness - 16% ISO and opacity - 98%. Higher values of these operating parameters would degrade the fibre characteristics such as zero-span tensile breaking length, tensile index, and sheet density. <![CDATA[<strong>Effect and mechanism of nanosize copper oxide on some physical and mechanical properties of flakeboards</strong>]]> The effects of nanosize copper oxide and basic copper carbonate on the physical and mechanical properties of flakeboards were investigated according to ASTM Standard D-1037, and the curing process of phenol formaldehyde (PF) resin containing copper compounds was further investigated using dynamic differential scanning calorimetry (DSC). The results showed that nanosize copper oxide had no or slightly beneficial effects on the mechanical properties and dimensional stability of the flakeboards. While basic copper carbonate increased thickness swelling and water absorption to some extent, the difference was not statistically significant. The DSC results indicated that the comparable activation energy and reaction enthalpy, obtained from nanosize copper oxide treated samples, contributed to the higher degree of conversion of PF resin and undiminished bonding strength of flakeboards, which is probably related to the acceleration of the addition reactions taking place among small molecules in PF resin and the enhancement of heat transfer of composite mat caused by nanosize copper oxide. <![CDATA[<strong><i>Radial and longitudinal basic density variation in 16 years old Eucalyptus regnans trees</i></strong>]]> La variación radial y longitudinal de la densidad básica de la madera, a lo largo del fuste, fueron determinadas en árboles de una plantación de Eucalyptus regnans de 16 años, crecida en la Costa de la Provincia de Arauco, Chile. Además, se correlacionó la densidad básica promedio del fuste, con la densidad básica obtenida a distintos niveles de altura. Se muestrearon 9 árboles entre dominantes y codominantes. De cada árbol se obtuvieron rodelas cada 10% de la altura total, hasta una altura del 70%. De las rodelas se extrajeron cubos de 1 cm de arista, de médula a corteza en las direcciones norte y sur, y en ellos se determinó la densidad básica. Se encontraron tres patrones de variación radial para la densidad básica a lo largo del fuste del árbol. En la dirección longitudinal la densidad básica disminuyó desde la base del fuste hasta la altura del 4,5% y luego aumentó linealmente hasta el 70% de la altura total del árbol. Las mejores alturas de muestreo para estimar la densidad promedio del fuste, fueron al 10 y al 20% de la altura total del árbol.<hr/>The radial and longitudinal variations in wood basic density along the stem were determined in trees from a plantation of Eucalyptus regnans (16 year old) grown at the coast of the Arauco Province, Chile. The weighted stem basic density was estimated and correlated to the basic density at different sampling heights. Nine dominant and/or codominant trees were selected. Discs were obtained each 10% of the total height until a height of 70%. From the discs, small cubic samples of 1 cm edge from the pith to the bark and in the north and south directions were extracted, and in these small samples the basic density was determined. Three radial variation patterns for the basic density along the stem were found. In the longitudinal direction, basic density decreased from the base of the tree to 4.5% of the height, and then increased linearly until 70% of the total tree height. The best sampling heights for estimating the weigthed basic density of the stem were to 10 and 20% of the total tree height. <![CDATA[<strong>Effect of sodium sulfite charge in NSSC pulping of </strong><em><b>E. globulus</b></em>]]> El presente trabajo tuvo como principal objetivo determinar el efecto de la adición de una alta carga de sulfito de sodio (Na2SO3) para la sustitución de otras fuentes alcalinas (Na2CO3 o NaOH) sobre el pulpaje de alto rendimiento al sulfito neutro. En la etapa química se utilizó sólo sulfito de sodio (Na2SO3) como agente deslignificante y en la etapa mecánica un refinador Bauer de 12". Se obtuvieron pulpas con rendimientos variables entre 70 y 90 % y se verificó que las propiedades físico-mecánicas de las pulpas aumentan considerablemente a medida que el rendimiento baja. Al mismo tiempo disminuyeron, notablemente, el consumo energético de desfibración y el de refinación. Pulpas con rendimientos cercanos al 80%, fabricada con una alta dosis de sulfito de sodio presentaron propiedades físico-mecánicas similares a una pulpa química. La mayor carga de sulfito no significó un aumento considerable del consumo de reactivos, especialmente a altos rendimientos. El buen desarrollo de propiedades físico-mecánicas se debe, probablemente, a la alta proporción de hemicelulosas que presenta la pulpa y a la selectividad del proceso para remover lignina desde la lámina media, lo que favorece la obtención de fibras íntegras y con un menor esfuerzo mecánico.<hr/>This paper presents experimental results on the effect of adding high doses of sodium sulphite (Na2SO3) to replace other sources of alkali, such as Na2CO3 or NaOH, in high-yield Neutral Semichemical Pulping (NSSC) process. Sodium sulfite (Na2SO3) was used as delignification agent in the chemical stage of eucalyptus globulus pulping. A 12" Bauer refiner was employed in the mechanical stage. Pulp yields ranged within 70-90% and, results show that physical and mechanical properties increased significantly as yields decreased. Moreover, the defibration energy consumption and beatings energy also showed a significant decrease. Those pulps featuring yields near 80%, obtained with high sodium sulfite loads, presented similar physical and mechanical properties as chemical pulps. At the largest sulfide dose used here, no significant increase in chemical consumption was observed, especially at high yields. This study shows that physical and chemical properties are enhanced by high hemicelluloses content, and process selectivity to remove lignin from the middle lamella, which leads to a fiber integrity and reduced mechanical stress.