Scielo RSS <![CDATA[Maderas. Ciencia y tecnología]]> vol. 16 num. 4 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<strong>Integridad científica</strong>: <strong>principio que inspira el prestigio</strong>]]> <![CDATA[<strong>Effect of ultrasound pretreatment on wood prior to vacuum drying</strong>]]> The influence of ultrasonic pretreatment prior to vacuum drying of Chinese fir specimens was examined in this work. In the pretreatments, wood samples were immerged in a distilled water bath and were treated using two wave frequencies for four different elapsed times to investigate effects of ultrasonic frequency and treatment duration. Then the wood samples were vacuum-dried at 80°C and absolute pressure of 0,05 MPa. After the pretreatment, microscopic analysis was carried out on the wood samples to check micro-cracks, the loss of extractives from the cell walls and other micro-structural changes on the wood. Results show that the ultrasonic treatment prior to vacuum drying significantly shortened the wood drying time. The drying time decreased with increase in the wave frequency and the treatment time. Furthermore, ultrasound pretreatment tended to reduce the content of extractives in the wood cell walls and cause cell-wall micro- cracking. <![CDATA[<strong>Efecto de las tensiones de crecimiento en el rendimiento y calidad del aserrado de </strong><em><b>Eucalyptus dunnii</b></em>]]> Se evaluó el efecto de las tensiones de crecimiento sobre la calidad y rendimiento de tablas de Eucalyptus dunnii aserradas verdes. Se muestrearon 45 árboles de un ensayo de 19 años situado en la Provincia de Corrientes, Argentina. Se aserró un rollizo (2 m de largo) por árbol para obtener tablas tangenciales de 2,54 cm de espesor. Se utilizaron los valores de tensiones de crecimiento GSI (CIRAD-Forêt) e índice de rajado en rollizo (IR) determinados sobre esos árboles en un trabajo previo. Se midió el largo de las tablas y de las rajaduras de cabeza. Se determinó el porcentaje de piezas con rajadura de cabeza (P), un índice que cuantifica las rajaduras para la totalidad de tablas aserradas (IRTC) y un índice que cuantifica las rajaduras para las tablas aserradas por rollizo (IRT). Se calculó el rendimiento en bruto del aserrado (R) y un rendimiento en calidad que excluye el defecto de las rajaduras de cabeza (RC). El IRTC fue de 54,4 mm/m y el IRT de 27,87 mm/m ± 19,85. Más de la mitad de tablas aserradas presentó rajaduras de cabeza (P: 58%), sin embargo el descenso del rendimiento del aserrado no fue pronunciado (R: 44,2% y RC: 41,7%). El IRT presentó una asociación moderada con las tensiones de crecimiento GSI e IR (r: 0,46 - 0,52).<hr/>The growth stress effects on yield and quality of Eucalyptus dunnii green sawn boards were evaluated. A total of 45 trees were sampled from a 19-years-old trial located at Corrientes, Argentina. Each tree was felled and cross-cut to produce a 2 m log. Subsequently each log was sawn to obtain tangential boards 2,54 cm thick. Growth stress indicator (GSI, CIRAD-Forêt) and log end split index (IR) values taken from these trees in a previous research were used. Length of boards and end checks were measured and the percentage of boards with end check (P) was determined. An index to quantify end checks for the whole sawn boards (IRTC) and another for the sawn boards per log (IRT) were calculated. Sawlog gross yield (R) and a quality sawlog yield (RC) which exclude the end check defects were calculated. The IRTC was 54,4 mm/m and the IRT was 27,87 mm/m ± 19,85. More than half of the boards had end checks (P); nevertheless the sawlog yield did not show a high decline (R: 44,2 % and RC: 41,7 %). The association between IRT and growth stress indicator GSI and log end split index IR was moderate (r: 0,46 - 0,52). <![CDATA[<strong>The effect of thermal treatment on physical and mechanical properties of </strong><i>Luehea divaricata</i><strong> hardwood</strong>]]> This study aimed to characterise the effect of thermal treatment on physical and mechanical properties of açoita-cavalo (Luehea divaricata) wood. To achieve this, samples were treated at 160, 180 and 200°C for 2 h in an oven (dry conditions). Physical and mechanical characterisation was performed by weight loss, dry specific gravity at 12%, equilibrium moisture content, volumetric swelling and shrinkage, water absorption, water repellence, static bending and brittleness tests. Roughness and colour tests were performed in order to evaluate the modified surface. Main findings showed that dimensional stability of thermally modified wood increased, while mechanical strength of wood decreased as a function of temperature. A darkening of wood and a decrease in roughness were observed. <![CDATA[<strong>Effect of precipitation pattern on leaching of preservative from treated wood and implications for accelerated testing</strong>]]> There is a need to develop improved accelerated test methods for evaluating the leaching of wood preservatives from treated wood exposed to precipitation. In this study the effects of rate of rainfall and length of intervals between rainfall events on leaching was evaluated by exposing specimens to varying patterns of simulated rainfall under controlled laboratory conditions. Lumber specimens were pressure-treated with 0,5; 1 or 2% solutions of chromated copper arsenate (CCA) and exposed to 762 mm of rainfall at rates of 2,5; 8 or 25 mm/h. Intervals between rainfall events were increased for some specimens. Leachate was periodically collected and analyzed to quantify leaching of arsenic, chromium and copper. The quantity of CCA elements leached, per unit rainfall, was consistently greatest at the lowest rainfall rate for all solution concentrations evaluated. Incorporation of additional time between rain events increased leaching at the lowest rainfall rate, but this effect was less noticeable as rainfall rate increased. The results of this study indicate that simulated rainfall leaching tests should be conducted using rainfall intensities at the lower end of those that are typical for the region of interest. The lengths of intervals between rainfall events may also increase leaching, but use of lengthy resting intervals conflicts with the goal of accelerated testing. Further research may be warranted to optimize time between rainfall events and assess the effect of drying periods between rainfall events. <![CDATA[<strong>Predicting the young’s modulus of defect free radiata pine shooks in finger-jointing using resonance frequency</strong>]]> In this paper, dynamic MOE and static MOE of short-length radiata pine specimens produced for finger jointing were measured using non-destructive technique and correlated to each other. In order to obtain reliable static MOE data, 36 mm thickness shooks as well as the matched samples of reduced thickness (15mm) were tested, and the effect of annual growth rings on dynamic and static MOE is also addressed. Mathematical correlations were fitted between the dynamic MOE for the 36 mm thick shooks and the static MOE of the 15 mm thick samples. The coefficient of determination for dynamic MOE group 4,00-7,99 GPa was the strongest (R2= 0,82) and the correlation strength was further improved for sorted quarter sawn samples (R2= 0,92). Finally, the correlation between static modulus of rupture (MOR) and dynamic MOE is discussed. <![CDATA[<strong>Effects of veneer drying at high temperature and chemical treatments on equilibrium moisture content of plywood</strong>]]> Moisture content (MC) is one of the most important factors that can affect many physical and mechanical properties of wood and veneers. MC strongly affects the final strength and durability of joints, development of surface checks in the wood and dimensional stability of the bonded assembly. In this study, plywood panels made from Alnus glutinosa (alder), Fagus orientalis (beech) and Picea orientalis (spruce) wood veneers were treated with ammonium acetate, borax and boric acid by using dipping method to test for their equilibrium moisture content (EMC). Borax and boric acid solutions were used for fire-retardancy, and ammonium acetate for reducing formaldehyde emission. Two different veneer drying temperatures (20ºC and 180ºC) were used to reveal the effects of veneer drying at high temperature on the hygroscopicity of plywood panels. EMC values of alder, beech and spruce panels decreased significantly with veneer drying at high temperature. Picea orientalis (spruce) plywood panels had the highest EMC values and followed by Alnus glutinosa (alder) and Fagus orientalis (beech) panels. EMC values of plywood panels increased significantly for both drying temperatures after ammonium acetate, borax and boric acid treatments. <![CDATA[<strong>Color stability of weathered heat-treated teak wood</strong>]]> This study investigated the color stability in a heat treatment of teak wood (Tectona grandis) exposed to ultraviolet radiation under accelerated aging conditions. Nine trees from three different spacing levels were used. Samples of 150 mm x 75 mm x 20 mm were prepared and divided into two groups: heartwood and sapwood. Two levels of heat treatment (180 and 200°C) were used. The color was measured every 42 hours with a portable spectrophotometer using the CIE-Lab system. Accelerated aging was performed in a QUV/Spray chamber. The total cycle of exposure to ultraviolet radiation was of 168 hours at 340 nm. Tree planting spacing had no effect on color change after ultraviolet radiation. Untreated sapwood had greater color change than untreated heartwood. However, after heat treatment, sapwood showed high color stability, especially at a temperature of 180°C. <![CDATA[<strong>Valoración mecanotermica de una resina biodegradable como agente de acoplamiento de materiales compuestos celulosicos/polímero hidrofóbico</strong>]]> En la búsqueda de plásticos reforzados con fibras que sean más amigables con el medio ambiente, aquí se presenta el primer estudio que evalúa la posibilidad de utilizar la brea natural de pino (en forma pura o maleinizada) como agente de acoplamiento (biodegradable). Polipropileno (matriz) y fibra de agave (tequilana Weber) de desecho a diferentes concentraciones (agente de refuerzo), fueron acoplados con cada uno de los agentes utilizados; su efecto en las propiedades mecánicas se comparó con el de un agente comercial de polipropileno modificado (Epolene E-43). Igualmente se prepararon, materiales compuestos sin agente de acoplamiento como referencia genérica. El desempeño mecanodinámico y mecanoestático de los materiales muestra claramente el incremento de propiedades mecánicas con los 3 agentes utilizados. La brea maleinizada mostró similitud o ligera superioridad sobre el agente comercial en el efecto logrado. La afectación en cristalinidad por la presencia de la fibra y el agente de acoplamiento correspondiente, fue evaluada mediante calorimetría diferencial de barrido. La absorción de agua como función del tiempo, permitió medir de forma indirecta el cambio logrado en la superficie de los materiales, y un análisis de FTIR, la valoración de la interacción fibra-polímero obtenida con el agente de acoplamiento. Tal interacción lograda con los agentes de acoplamiento, pudo ser además apreciada utilizando microscopía electrónica de barrido. Los resultados alcanzados marcan el camino para poder usar resinas naturales biodegradables como agentes de acoplamiento en el área de plásticos reforzados con fibras celulósicas.<hr/>In the search of useful environmentally friendly fiber reinforced plastics, this is the first study that evaluates the capability to use natural pine rosin (in pure or maleated glycerol ester form) as a biodegradable coupling agent. Polypropylene as polymer matrix and discarded agave fiber (tequilana Weber) as reinforcing agent at different concentrations, were coupled with each one of the two rosins above mentioned; a commercial maleated polypropylene (Epolene, E-43) agent was used to compare their effect. As generic reference, composites without coupling agent were also tested. Mechanodynamic and mechanostatic tests clearly show an increment in mechanical properties of the composites, using any of the 3 coupling agents. The results obtained with maleated rosin were similar or slightly better than the ones obtained with the commercial agent for composites with high fiber content. Fiber content and coupling agent effect on composites crystallinity, was evaluated by differential scanning calorimetry. In addition, water absorption as a function of time was followed to evaluate the effect of surface modification, and FTIR analysis allowed the observation of the fiber-polymer matrix interaction that was promoted with the coupling agents. The effect of such interaction obtained with the different coupling agents, was observed by scanning electron microscopy. The results show the feasibility to use the natural pine rosin in pure or modified form as biodegradable coupling agents. <![CDATA[<strong>Microfibril angle of </strong><em><b>Eucalyptus</b></em> <em><b>grandis </b></em><strong>wood in relation to the cambial age</strong>]]> The microfibril angle (MFA) of wood is an important feature, which helps to explain the physical and mechanical behaviour of wood in use. It has been little investigated for wood produced in Brazil, mainly for mature trees. Thus, the objective of this study was to analyze the MFA of Eucalyptus grandis at age 25 years in relation to the cambial age. One disk was cut from the base of the stem from each of three trees, where growth rings were marked. From a central strip 3,0 cm wide, 1 cm³ blocks were removed from each growth ring. After sectioned on the tangential face with a sliding microtome, sections of 8 μm thick were macerated. The individual fibres were observed by polarized light microscopy for measurement of MFA. According to the results, i) the MFA decreased from 29,3° (ring nº 1) to 18,9° (ring nº 25); ii) MFA can be estimated by the cambial age - a, according to the equation MFA = 28,1 - 0,35 × a, with R² = 94,7%. <![CDATA[<strong>Influence of residual lignin content on physical and mechanical properties of kraft pulp/pp</strong> <strong>composites</strong>]]> The effect of residual lignin content on the mechanical strength and water absorption of kraft pulp/polypropylene composites was studied. To meet this objective, hornbeam wood chips were converted to kraft pulp at three different alkalinities (15, 20, and 25%) and three different cooking times (60, 90, and 120 min). The residual lignin contents of these pulps were determined according to the TAPPI standard. Kraft pulp was mixed with polypropylene (PP) at 50% weight ratios. The amount of maleic anhydride (MAPP) coupling agent was fixed at 4 per hundred compounds (phc) for all formulations. The results indicated that the lignin residual content decreased with increasing cooking time and alkalinity in kraft pulp. Also, it was found that tensile strength, tensile modulus, flexural strength, and flexural modulus were increased by increasing the alkalinity and cooking time; however, the notched impact strength and water absorption decreased. Overall, decreasing the lignin content had a positive impact on the flexural and tensile properties and had a negative effect on the notched impact strength.