Scielo RSS <![CDATA[Maderas. Ciencia y tecnología]]> vol. 18 num. 2 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[<strong>Hygromechanical strains during the drying of </strong><em><b>Eucalyptus nitens</b></em><strong> boards</strong>]]> Collapse and drying stresses are currently induced during the drying of Eucalyptus nitens in solid wood products. The purpose of this study was to investigate these drying stresses by measuring hygromechanical strains during the drying of Eucalyptus nitens boards. Small samples of Eucalyptus nitens wood were oriented in the radial and tangential directions and tested to determine the hygromechanical strains during the drying process. This experimental work consisted of cantilevered bending tests conducted under variable relative humidity conditions. Tests were performed in a conditioning chamber at 30 °C with an equilibrium moisture content ranging from 22 to 12% under four levels of stress: 0, 10, 20 and 30% of the rupture load. The strains were determined using strain gauges, and the total deflection was measured with a linear variable differential transformer. The results show that in hygromechanical strains during the drying of Eucalyptus nitens, both the surface deformation and mechano-sorption strain were found to be proportional to the applied stress and reached their maximum values in the tangential direction. The total deflection increased 0,18 mm/mm with a surface deformation of 0,20 mm/mm, and the mechano-sorptive strain provides a greater contribution with a value of 0,11 mm/mm, thus corresponding to 59% of the total deformation. In attempts to improve the drying schedules of Eucalyptus nitens to develop solid wood products, mechano-sorptive behavior may be applied to relieve collapse and drying stress. <![CDATA[<strong>Thermogravimetric analysis of anningre tannin resin</strong>]]> Three formulations of aningre tannin resins containing in order the paraformaldehyde powder, hexamethylenetetramine and aqueous glyoxal as hardeners were developed. Their thermogravimetric analysis have shown that they begin to decompose respectively from 135°C, 145°C and 140°C. About 24%, 40% and 39 % solid residues of their initial masses exist at the end of the analysis. Thermomechanical analysis has shown that the formulation containing paraformaldehyde powder as hardener has the best rigidity and the worst contains the hexamethylenetetramine. All formulations have different thermal degradation, differences were more significant between 400 and 900°C. The decomposition of hardeners become more significant from 400°C. <![CDATA[<strong>Surface properties of bamboo and Scots pine impregnated with boron and copper based wood preservatives after accelerated weathering</strong>]]> In this study, we investigated the color, gloss and surface roughness of bamboo (Phyllostachys bambusoides) and Scots pine (Pinus sylvestris) samples impregnated with boron and copper based preservatives during accelerated weathering from 168 h to 672 h. Tanalith-E, ACQ, wolmanit-CB were used as copper-based chemicals, while a mixture of boric acid and borax (7:3; w/w) was used as the boron compound. Results showed that retention values of bamboo samples were lower than the retention values of Scots pine samples probably due to the bamboo's anatomical structure and penetration characteristic. Bamboo surfaces became rougher and darker after impregnation and accelerated weathering compared to initial surfaces. Longer accelerated weathering periods seemed to have not a considerable effect on surface roughness of bamboo samples impregnated with copper based preservatives. Gloss of impregnated Scots pine samples increased with longer accelerated weathering period while gloss of bamboo samples decreased slightly with longer accelerated weathering period. Wolmanit-CB seemed to be most effective wood preservative for hindering color change and ensuring smooth surfaces after accelerated weathering. Color changes caused by accelerated weathering tended to be greater for impregnated bamboo samples than impregnated Scots pine samples. <![CDATA[<strong>Influence of wood sample size and species on the leaching of chromium and copper using different lab tests</strong>]]> The present study deals with the development of standardized laboratory methods to predict depletion of biocides more accurately under service condition. Laboratory test was conducted with EN 252 standard and non-standard pine as well as spruce specimens to determine leaching of chromium and copper from stakes pressure impregnated with commercial copper- and chromium-containing preservative. Two modified laboratory test methods were carried out; first discontinuous (CEN/TS 15119-1) and second continuous water immersion (CEN/TS 15119-2). Results showed that leaching of copper in pine sapwood specimens was higher than that in spruce specimens. Moreover, copper leaching was greater in comparison to leaching chromium. <![CDATA[<strong>Effect of the Brazilian thermal modification process on the chemical composition of </strong><em><b>Eucalyptus grandis</b></em><strong> juvenile wood</strong>: <strong>Part 1: Cell wall polymers and extractives contents</strong>]]> This article reports the first study of the influence of the Brazilian process of thermal modification called VAP HolzSysteme® on the chemical composition of Eucalyptus wood. Flatsawn boards of Eucalyptus grandis juvenile wood were tested for four treatment levels: untreated and thermally modified at final cycle temperatures of 140, 160 and 180 °C. Chemical analyses were carried out according to the standards of the Technical Association of the Pulp and Paper Industry and encompassed total extractives, insoluble lignin, holocellulose (cellulose + hemicelluloses) and solvent soluble extractives in water (cold and hot) and ethanol:toluene (1:2 v.v.) mixture. The chemical composition of thermally modified Eucalyptus grandis juvenile wood was significantly changed by the VAP HolzSysteme® process compared to untreated wood. Only the wood thermally modified at final cycle temperature of 180 °C was significantly different for all the chemical analyses performed compared to untreated wood. <![CDATA[<strong>Effect of the Brazilian thermal modification process on the chemical composition of </strong><em><b>Eucalyptus grandis</b></em><strong> juvenile wood</strong>: <strong>Part 2: Solubility and ash content</strong>]]> This article reports continuation of a study of the influence of the Brazilian process of thermal modification called VAP HolzSysteme® on the chemical composition of Eucalyptus wood. Flatsawn boards of Eucalyptus grandis juvenile wood were tested for four treatment levels: untreated, and thermally modified at final cycle temperatures of 140 °C, 160 °C or 180 °C. Chemical analyses were carried out according to the standards of the Technical Association of the Pulp and Paper Industry and encompassed 1% NaOH solubility and ash content. The 1% NaOH solubility increased in the wood thermally modified at 140 °C and 160 °C in relation to the untreated wood, but did not increase further 180 °C, indicating that the treatment at 180 °C was not enough to cause more degradation of hemicelluloses. In practice, the thermal modification process had no effect on the ash content of wood. The statistical difference observed between the treatment levels untreated and 160 °C (0,04 percentage points) can be attributed to the heterogeneity of wood as a material. <![CDATA[<strong>Thermal analysis of Oriental beech wood treated with some borates as fire retardants</strong>]]> Wood is widely used as a construction material for many applications. To have knowledge about the thermal degradation characteristic of wood could be crucial for indoor and outdoor applications. Chemical treatments could improve the resistance of wood against fire and heat. In this study, to investigate the thermal properties of Oriental beech (Fagus orientalis) wood treated with 0,25%; 1% and 4,70% aqueous solutions of boric acid, borax, disodium octaborate tetrahydrate and mixtures of and in different proportions, thermogravimetric analysis, differential-thermogravimetry, and differential-thermal analysis were performed. Our results showed that borate treatment decreased the Tmax (maximum degradation temperature) and increased residual char amount. Higher concentration levels of borates resulted in higher char content of Oriental beech wood specimens. Residual char content of borate treated wood samples at fixed concentration of 4,70% ranked as in the following order: disodium octaborate tetrahydrate > boric acid + borax (7:3) > boric acid + borax (1:1) > boric acid > borax > Control. The highest residual char content was achieved for the sample impregnated with 4,70% disodium octaborate tetrahydrate among the all treated samples. <![CDATA[<strong>Preservation trial for wood treated with Zn and Mn and effectiveness of treatment with borax to prevent leaching after five years of contact with soil</strong>]]> A través de un ensayo de campo implementado de acuerdo a la norma EN 252, se evaluó la efectividad de tratamientos en etapas, tendientes a disminuir la lixiviación de una solución rica en Zn y Mn obtenida a partir de un proceso de reciclado aplicada en la madera por el método Bethell. La segunda etapa antilixiviante agregó bórax por pincelado o por el método Bethell. Se utilizó madera de Pinus taeda. Este trabajo presenta el análisis de la evolución del proceso de deterioro a lo largo de 5 años de ensayo de campo y su evaluación. Se utilizó el índice climático de Scheffer como método de evaluación del riesgo microbiológico en el sitio del ensayo y se realizó un análisis microscópico de la madera, para verificar el tipo de deterioro presente. Los tratamientos al 3% y al 6% en Zn con agregado de bórax por el método Bethell fueron los de mejor desempeño entre los evaluados a pesar de no haber superado el desempeño del preservante de referencia. Se observó la presencia de los tres tipos de pudrición, blanca, marrón y blanda tanto en controles sin tratamiento como en maderas tratadas, en un sitio con condiciones intermedias para el deterioro.<hr/>The effectiveness of treatments in stages aimed at reducing the leaching of a solution rich in Zn and Mn obtained from a recycling process introduced into the wood by the Bethell method and a second stage in which borax was added by brushing and by the Bethell method, was evaluated through a field test. Pinus taeda wood was used according to EN 252 (1989). This paper presents an analysis of the evaluation and evolution of the process of deterioration over 5 years test. Scheffer climate index was used as a method of microbiological risk assessment at the site of the test and microscopic analysis of wood was carried out to verify the type of damage. Treatments 3% and 6% in Zn with borax added by the Bethell method were the top performers among the evaluated none of them performed better than the reference preserver. The presence of the three types of rot, white, brown and soft both on untreated controls and treated wood, in a site with intermediate conditions for microbial deterioration was observed. <![CDATA[<strong>Dimensional stabilization of wood treated with tall oil dissolved in different solvents</strong>]]> Many water repellents, such as classic wood preservatives have the disadvantage of being harmful to the environment. Therefore, interest increased even eco-friendly, or of biodegradable material. Natural oils (tallow, linseed oil), appears to be capable of preventing the wood water uptake. However, the total amount of oil required to achieve a high penetration of the sapwood. The aim of this study was to investigate the water repellent efficiency of tall oil dissolved in different solvents. As solvents ethanol, methanol, acetone and tall oil water emulsions were used. Scots pine and Uludag fir sapwood samples were impregnated with tall oil formulations. For this purpose we used tall oil/solvents (W/W) at the concentrations of 10% and 20% respectively. Test samples cut into small sizes (20 x 20 x 10 ± 0,2 mm) for water uptake and tangential swelling tests. The tests were carried out based on American Wood Protection Association (AWPA) standard E4 (2003). <![CDATA[<strong>Strategic planning for community sustainability in model forests: Case study of the Yoro model forest, Honduras</strong>]]> This study proposes the strategic planning process for development in model forests, based on the case study of the Yoro Model Forest in Honduras. In this forest the timber industry -and specifically the carpentry and furniture subsector- has the greatest competitive potential for supplying products for export and generating wealth in the area, given the region's scant purchasing capacity. Strategic analysis, strategic choice and strategic implementation are applied to this subsector, and the results show that the subsector could be developed by creating a cooperative enterprise capable of supplying furniture parts to an international company whose marketing strategy includes the sale of natural, environmentally-sustainable furniture, and which has a policy of social engagement. <![CDATA[<strong>Microscopic investigation of defects in thermally compressed</strong> <strong>poplar wood panels</strong>]]> The combined effects of temperature and compression on the microstructure of solid-wood panels produced by Aspen (Populus tremula) wood were evaluated. Thermal compression was applied on aspen wood to increase the density for improving its physical and mechanical properties. The solid wood panels with dimensions of 100 mm by 500 mm by 25 mm were hot-pressed by using a laboratory hot press at a temperature of either 150°C or 170°C and pressure of either 1MPa or 2 MPa, respectively, for 45 min. Changes in the microstructure were detected by using a light microscope. The microscopic investigations revealed that the wood exhibited much defects in the process conditions of 170ºC / 2 MPa, and the distribution of defects were not uniform in the growth rings of the wood specimens in the two treatment groups. All defects in cell structure were quite distinct in the beginning and the last parts of the growth rings and the largest damages occurred in the fibers and vessels for the two process conditions. The results indicate that growth ring structure, vessel porosity, and cell wall thickness have a strong effect on wood behavior in various process conditions. <![CDATA[<strong>Performance of copper azole treated softwoods exposed to marine borers</strong>]]> Wooden material has been used for shipbuilding and structural purposes in the marine environment since ancient times. Wood being used in the sea water can be damaged by marine wood boring organisms, which can turn marine wooden structures unserviceable with great economic cost. Using naturally durable species and preservative treated wood can increase the service life of wooden maritime structures and avoid or minimise the damages caused by marine borers. In this study, Scots pine (Pinus sylvestris), Black pine (Pinus nigra) and Turkish fir (Abies bornmülleriana) naturally grown and economically important wood species in Turkey were treated with copper-azole and evaluated in marine trials for 7 and 14 months in the Western Black Sea region. In this experiment, Teredo navalis was the only teredinid species identified. Copper- azole treated fir and Scots pine specimens suffered no attack, after 7 and 14 months exposure, except four panels which suffered minor damage. However, copper-azole treated Black pine panels were moderately damaged, and all of the control panels of the softwoods were strongly attacked. The average largest shell diameter was found to be 4,79 mm in Scots pine, while the longest pallets (4,71 mm) was found in Black pine. All untreated test panels scored an average of 4 (heavily attacked) after a 14 month period. The cellulose ratio of Black pine decreased from 56 % to 50 %, and the holo-cellulose ratio from 76 % to 71 %. The treated samples showed resistance against marine borers although the copper (cu) leaching was high during the 14 months exposure underwater. <![CDATA[<strong>Stress characteristics and stress reversal mechanism of white birch (</strong><em><b>Betula platyphylla</b></em><strong>) disks under different drying conditions</strong>]]> Drying stress is the main cause for the generation of drying cracks in wood disks during drying, which limits the processing and utilization of this valuable material. For this study, white birch disks with one trunk and a thickness of 30 mm were dried under three different drying conditions: 1) a very slow drying process preventing the generation of a radial moisture content (MC) gradient, 2) a drying process with slowly increasing temperature leading to a radial MC gradient, with a higher MC in the heartwood, and 3) the same heat drying process but the wood disks were partly covered with a thin plastic film prior to the drying process leading to a reversed radial MC gradient, i.e., a higher MC in the sapwood. For each drying condition, the tangential elastic strain in the wood disks was investigated for a mean MC of 26%, 18% and 10%, respectively, as a function of the radial distance from the pith in order to predict the drying stress. Furthermore, the stress characteristics and stress reversal mechanisms in wood disks are discussed in this paper with the help of stress analysis sketches. <![CDATA[<strong>Differences in dynamic modulus of elasticity determined by three vibration methods and their relationship with static modulus of elasticity</strong>]]> Dynamic modulus of elasticity was determined in clearwood samples of eight tropical hardwood species using longitudinal vibrations, flexural vibration and ultrasonic transit-time methods. These samples were subsequently subjected to three point static bending test to determine static modulus of elasticity and modulus of rupture. Acoustic velocity and wood density were found to be independent parameters as the velocity was nearly the same in wood with distinctly different densities. Among the three dynamic measurements, modulus from the ultrasonic method was the highest followed by the longitudinal vibration and flexural vibration. Any of three vibration methods could be used to predict static modulus as they exhibited a near perfect correlation with static MoE. However, the dynamic modulus determined by different vibration methods were found to diverge with increasing static modulus. Wood density was the dominating factor influencing both modulus of elasticity and modulus of rupture. <![CDATA[<strong>Variations in wettability on heat-treated wood surfaces</strong>: <strong>Contact angles and surface free energy</strong>]]> Fueron determinados los ángulos de contacto de las maderas Pinus (Pinus taeda), Erisma (Erisma uncinatum), Araucaria (Araucaria angustifolia) e Hymenaea (Hymenaea stilbocarpa) en cuatro líquidos de pruebas (agua, diyodometano, formamida y etilenglicol). Los valores de energía libre superficial fueron calculados en las maderas sometidas al tratamiento térmico, teniendo en cuenta los cambios en sus componentes polares y apolares (dispersivas). De acuerdo con los resultados del ángulo de contacto, energía libre superficial y polaridad superficial, las maderas se mostraron poco mojables después del tratamiento térmico, transformándose en hidrofóbicas. Las maderas Pinus y Araucaria se mostraron más polares y presentaron bajos valores de ángulo de contacto y alta mojabilidad (más hidrofílicas). Los valores de energía libre superficial obtenidos a partir de las medidas de ángulo de contacto mostraron una dependencia por el uso de dos, tres o cuatro líquidos de prueba, produciendo diferentes perfiles de los componentes de la energía libre superficial. Las características superficiales de las maderas fueron definidas con base en sus valores de polaridad superficial, un parámetro importante para inferir cuales maderas son más apolares (más hidrofóbicas), o sea, de mayor interés tecnológico.<hr/>The contact angles for Pinus (Pinus taeda), Erisma (Erisma uncinatum), Araucaria (Araucaria angustifolia) and Hymenaea (Hymenaea stilbocarpa) woods were obtained using four test liquids (water, diiodomethane, formamide, and ethylene glycol). The values of surface free energy were calculated for the heat-treated woods in order to analyze their changes in polar and non-polar (dispersive) components. According to the results of contact angles, surface free energies and surface polarities, the woods showed reduced wettability after heating treatment and become hydrophobic. Pinus and Araucaria were by far the most polar samples, since they presented low values of contact angle and high wettability (more hydrophilic). The approach used to calculate the surface free energy from the measurements of contact angle depends on the use of two, three or four test liquids, since different profiles were obtained for their polar and non-polar components. The surface characteristics for the wood samples were mainly defined based on polarity, which is an important parameter aiming at inferring when they are more polar (more hydrophobic), i.e. of great technological interest.