Scielo RSS <![CDATA[Maderas. Ciencia y tecnología]]> vol. 21 num. 1 lang. es <![CDATA[SciELO Logo]]> <![CDATA[Evaluation of the strength, sorption and thermal properties of bamboo plastic composites]]> Abstract: Natural fiber plastic composites were made from Nigerian grown bamboo (Bambusa vulgaris) and high density polyethylene (HDPE) by extrusion and evaluated for strength, sorption and thermal properties. Composites were manufactured using two different screened bamboo particle size fractions (&lt;2 mm and &lt; 0,5 mm). The composites were tested for flexural properties, water sorption, melt flow and thermal properties. The melt viscosities at 190oC were 22,3 ± 0,91 kPa·s (&lt;2 mm) and 27,4 ± 1,2 kPa·s (&lt;0,5 mm). The results obtained indicated that the composites made with the smaller particle size fraction had higher flexural strength (37,4 ± 1,0 MPa) and modulus of elasticity (2,0 ± 0,2 GPa) than those made with the larger particle size fraction (29,9 ± 1,1 MPa and 1,7 ± 0,1 GPa). Dynamic mechanical analysis (DMA) also showed higher dynamic storage modulus for the &lt;0,5 mm particle-based composites than those made from the &lt;2 mm particle size fraction due to higher density and better interfacial interaction between the fiber and matrix. Also, the composites made with the smaller particles and were more dimensionally stable (water absorption of 5,4% versus 18,5% at 61 d). The bamboo composites had thermal stability range of 265 - 279oC (onset degradation temperature). The composites made with the smaller bamboo particles possessed the better properties in comparison with those made from the &lt;2 mm. Particle size and density significantly affected the mechanical, physical, thermal and rheological properties of the composites evaluated. <![CDATA[Study on compressive stress relaxation behavior of beech based on the finite element method]]> Abstract: The compressive stress relaxation behaviors in three directions of beech (Fagus orientalis) were studied by experiments, and predicted by mechanical model and finite element method. Firstly, short-term (3 hours) compressive stress relaxation experiments were carried out in longitudinal (L), radical (R) and tangential (T) directions of beech, and then the experimental data was fitted by mechanical model with two single Maxwell bodies in parallel connection. Secondly, the method of predicting the long-term (12 hours) stress relaxation behaviors of beech based on the finite element method was studied using the experimental data of short-term stress relaxation. Finally, the long-term stress relaxation behaviors in three directions of beech were investigated by experiments, mechanical model and finite element method respectively, and the results of them were compared. The results showed that stress relaxation behaviors of beech were different in three directions, and the short-term stress relaxation in L was much smaller than those in R and T directions under the same load. Besides, the mechanical model with two single Maxwell bodies in parallel connection was capable of predicting the short-term relaxation behaviors of beech in three directions with correlation coefficients beyond 0,99 but it did not work in long-term relaxation. In addition, the errors of FEM were smaller than those of the mechanical model compared with the results of experiments in the long-term stress relaxation, and the errors of the FEM were approximately 8% in L and 20% in R and T directions, which were all accepted in the field of wood engineer. This study will contribute to predict the long-term relaxation behaviors of wood products and wooden structures based on the FEM. <![CDATA[Investigation of some surface properties and thermogravimetric analysis of veneer sheets treated with fire retardants]]> Abstract: This study investigated the effects of different fire retardant chemicals on surface and thermal properties of veneer sheets. Beech (Fagus orientalis), alder (Alnus glutinosa), poplar (Populus deltoides) and scots pine (Pinus sylvestris) were chosen as wood species and zinc borate, borax, monoammonium phosphate and ammonium sulfate were chosen as fire retardant chemicals. The samples were impregnated by using the immersion method. Some surface properties such as colour measurements and surface roughness of the veneer sheets were conducted according to CIE L*a*b* system. Some thermal properties such as thermal conductivity of the veneer sheets were conducted according to standard and weight loss after combustion was determined by thermogravimetric analysis (TGA). Conforming to the results from the study, it was found that fire retardant chemicals increased the thermal conductivity and surface roughness of veneer sheets. Also, TGA experiments showed that all of the fire retardant chemicals decreased the loss in weights. <![CDATA[Relationship between the dynamic and static modulus of elasticity in standing trees and sawn lumbers of <em>Paulownia fortune</em> planted in Iran]]> Abstract: This paper aims to introduce a relationship between the dynamic modulus of elasticity in healthy standing trees of Paulownia fortune (planted in Iran) and the static modulus of elasticity in sawn wood. For this reason, a stress-wave non-destructive testing technique was carried out in longitudinal and transverse directions in 14 trees into two diameter classes (25-31 cm and 32-38 cm) at breast height and in logs at different height of stem to measure the stress wave speed and consequently, dynamic modulus of elasticity. Then, static modulus of elasticity of samples was calculated using 3-point bending tests in the sawn wood. The results revealed that the stress-wave speed and dynamic modulus of elasticity in logs of Paulownia are more than those of standing trees in longitudinal direction. Also, the diameter of the tree can significantly affect the stress wave velocity in standing trees and logs of Paulownia. Finally, a high correlation coefficient exists between static modulus of elasticity and dynamic modulus of elasticity (r= 0,68) in this tree. <![CDATA[An experimental and numerical study of moisture transport and moisture-induced strain in fast-grown Sitka spruce]]> Abstract: The use of fast-grown timber in the manufacture of engineered wood products is increasing; however, the fast growth rate results in a low-density timber that is susceptible to significant swelling and shrinkage deformations under changing moisture content. The current study focuses on the characterisation of the moisture diffusion and swelling/shrinkage of fast-grown Sitka spruce and the prediction of the moisture-induced strain development in Sitka spruce glulam beams under variable humidity cycles. Moisture content evolution and swelling/shrinkage coefficients were measured and the longitudinal swelling/shrinkage was found to be significantly greater than for slow-grown timber. Sitka spruce glued-laminated beams were subjected to controlled relative humidity cycling for 52 weeks and the moisture distribution and moisture-induced strains were measured continuously. Coupled moisture-displacement numerical models, incorporating the experimentally measured material parameters were developed. The effect of the glue-line was found to have an insignificant effect on moisture transport, however, the material orientation greatly influenced the predicted moisture-induced strain. Accurately mapping the material orientation produced significantly better predictions of the experimental results over the 52-week period. <![CDATA[Carbon stored by furnishing wood-based products: An Italian case study]]> Abstract: The concentration of atmospheric carbon dioxide is constantly rising, with severe effects on global climate change. To mitigate impacts of climate change, the role of forest in terms of carbon sequestration are well-known as trees naturally pull CO2 from the atmosphere as they grow. Contrarily, only recently the carbon mitigation value of wood-based products in buildings has been recognized. Buildings are a fundamental sector for wood-based products, both in terms of volume and service life length. In particular, furnishings in housing include high quantities of wood-based products; they are usually made, partly or entirely, by solid wood or by wood-based panels such as plywood, particleboard and medium density fiberboard. These wood furnishings store biogenic carbon during their service life. In this context, the present study investigated the amount of carbon stored by furnishing wood-based products for an apartment in Torino, Italy. The overall amount, determined according to European Standard, resulted in 3531 kg of CO2-equivalents stored. This corresponds to 45,8 kg per m2 of indoor walkable area; simulating lower and higher intensity usages of wood-based products provided carbon storage values of 35,1 and 55,3 kg/m2, respectively. On the whole, the present study gave an order of magnitude of the role played in carbon storage by furnishing wood-based products in building and illustrates their relevance in mitigating climate change. <![CDATA[Effects of saturated vapor pre-steaming on drying strain in Asian White Birch: Experimentation and modelling]]> Abstract: The effect of low pressure saturated vapor pre-steaming on restrained shrinkage strain, mechano-sorptive creep and the distribution of moisture content was investigated during conventional drying of wood discs. Mechano-sorptive creep was furthermore modelled by artificial neural network theory with five inputs, i.e., pre-steaming and drying temperatures, wood moisture content, relative humidity and distance from the pith. Results revealed that, pre-steaming partly reduced the variation of moisture content distribution along radial direction, increased restrained shrinkage strain in heartwood and decreased in sapwood and slightly decreased the mechano-sorptive creep. The neural network model provided reasonable prediction results, namely, the coefficient of determination for training, validation and test sets greater than 0,95. <![CDATA[Specific gas permeability of normal and nanosilver-impregnated solid wood species as influenced by heat-treatment]]> Abstract: The effect of heat treatment at 50 and up to 150°C was studied on dowel-shape specimens prepared from beech (Fagus orientalis), poplar (Populus nigra), and fir (Abies alba) wood. Specimens were cut into two diameter sizes (18 and 25 mm) to explore the effect of diameter size on permeability. Separate sets of specimens from each size and species were prepared to be first impregnated with a 200 ppm aqueous nanosilver (NS) suspension to investigate the effect of facilitated heat-transfer on permeability at different temperatures. Specimens were heated in five consecutive steps at 50, 75, 100, 125, and 150(C and for 24 hours in each step. High variance was found in the specific gas permeability between each treatment group, thus indicating probable high fluctuation in settlement of extractives at different spots of a log. Heat treatment only affected gas permeability at the first steps of heating (50 and 75°C), where loss of moisture content resulted in a permeability increase in nearly all species. Consecutive steps of heating up to 150(C did not significantly affect the permeability in either normal or NS-impregnated specimens. <![CDATA[Effectiveness of copper chrome arsenate and used engine oil in protecting fencing posts of Ugandan grown eucalypt clone GC550 and <em>Phoenix reclinata</em> against termite attack]]> Abstract: Eucalypts and Phoenix reclinata posts are the most commonly used species for fencing posts in urban areas of Uganda. Although eucalypts are known to be susceptible to termites, fencing posts are still used untreated. In this study, the effectiveness of Copper Chrome Arsenate and used engine oil in protecting Ugandan grown Eucalyptus grandis × Eucalyptus camaldulensis clone and Phoenix reclinata fencing posts against termite attack were assessed. The objectives were to determine (i) the incidence and (ii) severity of termite attack on Eucalyptus grandis × Eucalyptus camaldulensis and Phoenix reclinata fencing posts treated with Copper Chrome Arsenate or used engine oil. Ninety 2ft long samples of Eucalyptus grandis × Eucalyptus camaldulensis and P. reclinata posts were treated with Copper Chrome Arsenate or used engine and others left to act as control then buried in 1ft deep pits in the ground at a spacing of 1m by 1 in Eastern Uganda. The samples were visually inspected monthly for termite damage for 9 months. More than 80% of untreated samples of both species had been attacked by termites within the first month. Copper Chrome Arsenate treated Eucalyptus grandis × Eucalyptus camaldulensis and Phoenix reclinata samples were first attacked in the 8th and 5th months respectively. While used engine oil treated Eucalyptus grandis × Eucalyptus camaldulensis and Phoenix reclinata samples were first attacked in the 7thand 5th months respectively. The modal severity for samples of both species treated with either Copper Chrome Arsenate or used engine oil was class 1 (less than 1% of the sample volume eaten) while for the untreated samples it was class 5 (above 60% volume eaten) for the 9 months of field exposure. It was concluded that untreated posts of Eucalyptus grandis × Eucalyptus camaldulensis and Phoenix reclinata were highly susceptible to termite attack and that the protection offered by used engine oil or Copper Chrome Arsenate managed to restrict damage by termites to only less than 1% of the sample volume , over the 9 months of exposure for most of the sample posts. It is recommended that the experiment be repeated for a much longer period in order to ascertain the exact service life of the posts under these circumstances. Penetration and retentions of the preservatives in the posts should also be studied in order to ascertain their effect on the efficacy. <![CDATA[Application of paints to decrease air permeability of oriented strand boards]]> Abstract: The study is focused on the decreasing of oriented strand boards air permeability using paints. The oriented strand boards /3 (classification according to EN 300:2006) of 12 mm thickness was chosen for the measurement. Nine different paints were applied in one layer on one side of boards. The difference in air permeability of unpainted and painted boards was defined as paint impact in %. Paint impact ranged from 1,9 % to 78,6 %. Furthermore, the air permeability of 15 and 22 mm thick oriented strand boards /3 boards from another producer exhibiting better properties has been measured to compare. The best results of paint impact were obtained for latex paint (paint impact 78,6 %) and penetration 1 (paint impact 66,4 %). Decreasing of the air permeability of oriented strand boards applied in low-cost constructions by using inexpensive paints could significantly improve the insulating properties of the wall structure and thus contribute to the development of the concept of low-cost passive building. <![CDATA[Effect of adhesive quantity on selected physico-mechanical properties of Bamboo glulam]]> Abstract: This study was aimed at determining the optimal glue quantity for bamboo lamination. Bamboo laminated boards were produced using glue applied at three different rates: 150 g/m2, 200 g/m2 and 250 g/m2. The boards produced were evaluated for their physical (density, longitudinal, tangential, radial and volumetric shrinkage) and mechanical (impact bending strength, modulus of elasticity, modulus of rupture and maximum compressive strength parallel to grain properties. It was discovered that the boards were uniform in their investigated physical properties but the glue quantity significantly influenced both the impact bending strength and modulus of rupture of the boards. Based on the results, it was observed that the boards produced with glue applied at the rate of 200 g/m2 met all the technical specifications on the basis of the investigated physical and mechanical properties, hence, concluded to be the optimal glue quantity for bamboo lamination. <![CDATA[Stability of planed and precision planed solid wood surfaces due to wetting]]> Abstract: The upper cell layers of machined solid wood surfaces will usually be damaged and compacted due to cutting forces. The deformation zone may be instable due to temperature and moisture variations as a consequence of artificial surface treatment or environmental interaction. Therefore, an evaluation method of surface stability in this respect would be desirable. In the frame of the new developed surface roughness evaluation method an individual wetting procedure has been developed, whilst surfaces have been characterized by 3D roughness measurement. The stability of surfaces is characterized by appropriate roughness ratios measured before and after wetting. The core depth S k of the Abbott parameters is the most sensitive indicator to any changes in the deformation zone. Different machining processes may produce surfaces with different stability but wood species have also definite influence on the surface stability, probably due to their density and moisture conduction properties. Latter is supported by the fact that the half-time of moisture evaporation from surfaces may differ considerably. In these experiments, planed and precision-planed surfaces were compared. According to the working principle of the precision planers the planing tool is held stationary whilst the work piece does the feeding motion, thus the blade produces a very thin slice. Using this machine, the machining roughness can be reduced to minimum as it is possible to avoid formation of cycloid arcs (like in case of traditional planing) and also possible to avoid dust formation (like in case of sanding). Investigations were conducted on Norway spruce (Picea abies), larch ( Larix decidua ), scots pine (Pinus sylvestris), sessile oak (Quercus petraea), black locust (Robinia pseudoacacia), aspen (Populus tremula) and beech (Fagus sylvatica). Black locust and the sessile oak have had most stable surfaces by both machining methods. The deformation zone of precision planed surfaces has been proven to be more stable than the one of planed surfaces for all wood species.