Scielo RSS <![CDATA[Maderas. Ciencia y tecnología]]> vol. 21 num. 2 lang. en <![CDATA[SciELO Logo]]> <![CDATA[Dynamic and static mechanical properties of <em>Eucalyptus nitens</em> thermally modified in an open and closed reactor system]]> Abstract: Eucalyptus nitens is a fast growing plantation species that has a good acclimation in Chile. It is commonly used for pulp and paper, but there is a growing market for solid wood products made from this species and an interest on producing high quality material. Thermal modification technology have been used to obtain high quality product out of fast growing plantation species. In this study we modified Eucalyptus nitens to analyse the influences of the process conditions and evaluated its mechanical properties under several process conditions. The material was modified in a closed system under elevated pressure and controlled relative humidity (30 and 100% relative humidity) at temperatures between 150 and 170°C, and in an open system with a standard thermal modification procedure between 160 and 230°C. Modulus of elasticity, modulus of rupture, deflection and work in bending (in elastic and inelastic proportions) and the resistance to impact milling in high energy multiple impact tests were determined. Mass loss after each modification was also measured and correlated with the mechanical properties. Anatomical properties of selected modifications were analysed. There were no significant differences between open and closed system modifications in both mechanical and anatomical properties. <![CDATA[Toxicity potential of heartwood extractives from two mulberry species against <em>Heterotermes indicola</em>]]> Abstract: Choice and no-choice tests were run to evaluate natural resistance of the woods of two Morus species (Morus alba and Morus nigra) against the subterranean, Heterotermes indicola, under field conditions. Toxicity, antifeedant and repellency potential of the heartwood extractives was also investigated under laboratory conditions. Heartwood extractives were removed from wood shavings by using methanol or an ethanol: toluene (2:1) mixture. Results of choice and no-choice tests with sap and heartwood blocks exposed to termites, showed that both mulberry species were resistant to termites but in comparison, Morus alba wood was more resistant than Morus nigra to termite feeding as it showed &lt;5 % weight loss after 90 days. Termites exhibited a concentration dependent mortality after exposure to either mulberry species’ heartwood extractives. The highest termite mortality occurred after termites were exposed to filter paper treated with Morus alba extractives at a concentration of 5 %. At this concentration, antifeedancy and repellency were calculated to be 91,67 and 84 % respectively. . Our results also showed that extractives from either mulberry species imparted resistance to vacuum-pressure treated non-durable Populus deltoides wood. Termite mortality was greater than 75 % after feeding on Populus deltoides wood treated with extractives from Morus alba. Solvent only (methanol) treated Populus deltoides controls, showed a minimum weight loss of 2,69 % after 28 days. These results suggest that Morus alba extractives have antitermitic properties and may be potentially useful in the development of environment friendly termiticides. <![CDATA[Thermal degradation of oriental beech wood impregnated with different inorganic salts]]> Abstract: This study investigated the thermal properties of Oriental beech (Fagus orientalis) treated with (NH4)2HPO4, K2HPO4, NH4Cl and (NH4)2SO4 salts and their mixtures (1:1; w/w) aqueous solutions at 3% concentrations. The effects of different inorganic salts fire retardants on the thermal degradation characteristics of wood samples were evaluated by thermogravimetric analysis (TGA). Based on the TGA curve for untreated beech wood, weight loss takes place at three distinct steps. The impregnation of inorganic salts resulted in higher char yields and additional thermal degradation steps were identified. The highest char yield (80%) was obtained from (NH4)2HPO4-K2HPO4 mixture impregnated sample. Salt mixtures containing phosphates ((NH4)2HPO4 and K2HPO4) have remarkable effects on thermal stability of beech wood, whereas NH4Cl salt lowered the decomposition temperatures and char yield. <![CDATA[Process layout planning and optimised product range selection in manufacture of wooden construction sets]]> Abstract: This paper introduces a systematic deterministic framework for planning and the analysis of facility layouts aimed at manufacturing a variety of parts, being components of specific end products. The essence of the proposed approach lies in the decomposition of a traditional job-shop into layout modules of generic material flow patterns that inherently yields improved efficiency of the entire system. It entails the use of a relevant reasoning scheme based on production flow analysis and the method of hierarchical clustering of specified process routings for parts. The approach has been studied in the aspect of its application in an actual woodworking facility, dealing with fabrication of wooden toy sets. The respective workflows were subjected to the analysis in order to identify production bottlenecks using data derived from the real case study. As a result, the designated process layout alternatives have been evaluated in terms of assumed measures of the operational performance. An inseparable part of the research was exploring the capability for the optimum selection of a multi-part product mix, to be fabricated in defined time frames. In this regard, the usability as well as the computational efficacy of the integer linear programming modelling have been fully confirmed. The results gained show in particular that the suggested methodical scheme could be a useful tool in planning optimised manufacture of customised wood products of modular construction. <![CDATA[Surface properties of novel wood-based reinforced composites manufactured from crushed veneers and phenolic resins]]> Abstract: This study was performed to determine the surface properties of novel wood-based reinforced composites made from poplar veneers and phenolic resins. The veneers with different thickness (1,8; 4; 6; 8 mm) were finely crushed and then were impregnated with phenolic resins to achieve different resin loading (12, 14, 18%). Finally, they were laminated or random paved to manufacture novel wood-based reinforced composites with different target densities (900-1100 kg/m3). With increased veneer thickness or resin content, the hardness of novel wood-based reinforced composites decreased and their roughness increased. The increase of density contributed to the increased hardness and decreased roughness. The surface wettability of novel wood-based reinforced composites appeared to be closely related to their surface roughness. There was a negative correlation between contact angle and roughness. The novel wood-based reinforced composites prepared by laminated mat formation showed higher hardness, lower roughness than those by random mat formation. Such data of surface properties can be applied to design the novel wood-based reinforced composites products with desired quality and provide basic information for further panel processing. <![CDATA[Machining properties of <em>Melia dubia</em> wood]]> Abstract: In this paper result of working quality of Melia dubia is reported after testing them under six major wood working operations namely - planing, sanding, turning, shaping, boring and mortising based on Indian Standard. The wood performed extremely well under planing. In shaping, the performance was good enough. Though all the other operations yielded poor results, the composite rating factor which is an overall performance indicator was 35 % more than that of Tectona grandis. The ease of working is only 93 % compared to teak. The working quality index which was based on the composite rating factor and ease of working worked out to 107 taking Tectona grandis as 100 mainly because of the high performance under planing and shaping and good performance under sanding. <![CDATA[Characterization of thermally modified short and long rotation teaks and the effects on coatings performance]]> Abstract: Many wood processing industries use short rotation teak, which has lower quality especially in durability and dimensional stability. Heat treatment is an eco-friendly method to improve dimensional stability and durability of wood. The objectives of the study were to investigate the effects of thermal modification on chemical composition, colour, dimensional stability and durability as well as coating’s performance after accelerated weathering of short and long rotation teak for exterior utilization. In this study, the samples were heated in oven at 220 °C for 20 h under nitrogen atmosphere. Results showed that independently of growth conditions teak woods underwent hemicelluloses degradation and an increase of lignin content after heat treatment. Extractives contents were lower in short rotation than in long rotation teak, and decreased in all cases after heat treatments. Dimensional stability was considerably improved as indicated by anti-swelling efficiency values of 64,9% and 58,9% for short and long rotation teak, respectively. Heated teak woods were more resistant against Trametes versicolor and the durability of short-rotation teak increased from moderate to very durable. Coatings on heat treated teaks had better bonding quality and better photo-stability when compared to unheated. Heated short rotation teak could be considered for exterior application. <![CDATA[Biological resistance of heat-treated wood of <em>Pinus caribaea</em> and <em>Eucalyptus saligna</em>]]> Abstract: This study aimed to analyze the resistance of the thermally treated wood of Pinus caribaea and Eucalyptus saligna to the biological attack of wood rotting fungi. The heat treatment processes were carried out in electric oven under nitrogen atmosphere, starting from 100 °C until reaching each one of the final temperatures of the process: 120, 140, 160, and 180 °C. The resistance assays were performed for white rot, brown rot, and soft rot fungi. The increase in decay resistance was observed for heat-treated wood of Pinus caribaea at higher temperatures. On the other hand, Eucalyptus saligna showed increased resistance to rotting fungi at all tested temperatures, except for white and soft rot at 120 °C. In general, the heat treatment process showed good results for its use as a wood preservative method. <![CDATA[Assessing the natural durability of different tropical timbers in soil-bed tests]]> Abstract: Ground contact speeds up timber decay because of the large number of microorganisms in soil. This study, we assessed the natural durability of seven tropical species using the European standard EN-807 (2001). We embedded samples of Dalbergia granadillo, Cordia elaeagnoides, Swietenia humillis, Tabebuia donell-smithii, Hura polyandra, Enterolobium cyclocarpum and Tabebuia rosea and temperate species Fagus sylvatica (as a control) in sandy, clay-sandy-loam and clay-loam for 8, 16, 24 and 32 weeks. We evaluated durability of the samples by determining the mass loss and modulus of elasticity (MOE) loss. The results varied significantly (p &lt; 0,001) depending on timber species and soil type considered. The D. granadillo and C. elaeagnoides were the most durable, with mass losses of 4,5%; 6,5% and MOE losses of 4,5%; 20,5%; respectively. F. sylvatica, T. rosea and E. cyclocarpum samples were the least durable, with mass losses of 22,3-25% and MOE losses of 35,8-59,8% respectively. Decay was most aggressive in sandy-clay-loam soil followed by the clay-loam soil and finally the sandy soil. <![CDATA[Fibre morphological variations of some Nigerian guinea savannah timber species]]> Abstract: Fibre morphology of some Nigerian tropical timber species were evaluated to determine their potentials as suitable source of raw material for pulp and paper making. The fibre dimension of the species showed that Syzygium guineense had the longest fibre length (2,0 mm) followed by Anogeissus leiocarpa (1,75 mm) while Albizia zygia had the shortest fibre length of 1,05 mm. Irvingia gabonensis had the largest fibre diameter while Vernonia colorata had the smallest. Vitellaria paradoxa had the widest lumen of 8,87 µm while Irvingia gabonensis had the smallest lumen and thickest (6,87µm) cell wall while Vernonia colorata had the thinnest (4,40 µm). Albizia zygia had the most slender fibres while Vitellaria paradoxa had the most rigid fibres. All the species had narrow fibre lumens and the cell walls were thick, which may have given poor results to the pulp made from them. The results of the ANOVA showed that there was high significant variation in all the fibre dimensions and the derived values of the species. DMR test showed that no statistical difference existed in the fibre length of Isoberlina doka, Khaya ivorensis and Albizia zygia. However, Vernonia colorata, Irvingia gabonensis and Vitellaria paradoxa had similar fibre length as well as Afzelia africana and Lannea welwitchii. All the species passed the Runkel Ratio &lt; 1 acceptable values for paper making fibre except Vitellaria paradoxa and Anogeissus leiocarpa with RR value of 1,38 and 1,03. Syzygium guineense and Irvingia gabonensis passed FC &gt; 0,55 for an acceptable value for paper making. All the fibres were elastic except Vitellaria paradoxa and Anogeissus leiocarpa. <![CDATA[Scaling and modeling the creep of <em>Eucalyptus globulus</em>]]> Abstract: Eucalyptus, with the commercial name of Blue gum, is a viscoelastic material strongly influenced when under constant load (Creep), being this phenomenon - in the context of displacements - exacerbated with transient relative humidity (variations of the water content in the wood material). The evaluation of bending creep was done in indoor / constant and transient humidity conditions. In the latter, mechano-sorptive effect, the creep bending tests were done for a period of 60 days with cycles of wetting-and-drying. Each cycle has 7 days of duration. Defect free specimens with dimensions of 20 x 20 x 400 mm3 (approximately to the scale 1:10) of Eucalyptus globulus. wood species were used. To fit the creep behaviour and extrapolate results for different periods (1, 10 and 50 years) a survey of different numerical models was done. Rational, parabolic and polynomial functions were chosen. In bending, Blue gum wood species presented a behaviour without a creep limit, therefore labile. Through the models used for extrapolations a significant variability was found for different periods. Values of the main standard of wood design (Eurocode 5) were exceeded. The most consistent mathematical model was the rational model because it is the one that has led to closer and stable results. <![CDATA[Timber grading of <em>Pinus uncinata</em> , a lesser known pine species from the pyrenean mountain range]]> Abstract: Timber grading is an essential step into the value process to determine wood usability for structural uses. It requires well-described characteristics obtained easily by taking non-destructive measurements to quantify reliable indicators of mechanical properties. In this paper we present an approach based on both timber scale and clear-wood scale measurements using the case of Mountain pine (Pinus uncinata). An important experimental plan have been performed from collected trees of French and Spain Pyrenean regions allowing significantly the use of inter-correlations between measurements. The physical properties of clear wood present an important adaptation of tree growth condition with a lower modulus of elasticity as a consequence of microstructure at cell-wall level but a conventional modulus or rupture in bending for pines. However, the results on timber presents an important the difference between visual and machine grading for this species in view of mechanical properties considered. The results obtained also show possible improvement and limitations of current regulation in the grading mountain pine timber for structural use.