Important Wood Properties Research Articles

Instrumented microindentation – a versatile technique in the field of wood science and technology

Hardness is an important mechanical property of wood or other wood-based materials and it is also very important in the case of wood coatings. Different indentation methods for measurements of hardness and other mechanical properties have been utilised already for a long time. In the last 50 years the instrumented indentation was developed. Here, an indenter tests the surface of a specimen with a controlled load and movement, in order to assess its mechanical properties. Three ranges of instrumented indentation tests are distinguished. In the macro range, the force is higher than 2 N, in the micro range it is below 2 N and the depth of indentation must exceed 0.2 μm. When the indentation depth is lower than 0.2 μm, the indentation technique is called nanoindentation. There can be found thousands of scientific papers about applications of instrumented nanoindentation in research of a large variety of materials. Instrumented microindentation remained somehow in the shadow of nanoindentation, but yet, it is a highly versatile technique with potentials to study various (micro)mechanical properties. In this review, examples of possible applications of instrumented microindentation are presented, with a focus on investigations of wood, wood-based composites, surface coated wood and polymeric films. In the second part of this paper, as an illustration, investigations of a self-healing wood paint are shown. The cyclic method and a single-load indentation confirmed the different mechanical properties and good scratch resistance of the self-healing paint.

Comparative Transcriptomic and Metabolomic Analyses of Differences in Trunk Spiral Grain in Pinus yunnanensis.

Having a spiral grain is considered to be one of the most important wood properties influencing wood quality. Here, transcriptome profiles and metabolome data were analyzed in the straight grain and twist grain of Pinus yunnanensis. A total of 6644 differential expression genes were found between the straight type and the twist type. A total of 126 differentially accumulated metabolites were detected. There were 24 common differential pathways identified from the transcriptome and metabolome, and these pathways were mainly annotated in ABC transporters, arginine and proline metabolism, flavonoid biosynthesis, isoquinoline alkaloid biosynthesis, linoleic acid metabolism, phenylpropanoid, tryptophan metabolism, etc. A weighted gene coexpression network analysis showed that the lightblue4 module was significantly correlated with 2'-deoxyuridine and that transcription factors (basic leucine zipper (bZIP), homeodomain leucine zipper (HD-ZIP), basic helix-loop-helix (bHLH), p-coumarate 3-hydroxylase (C3H), and N-acetylcysteine (NAC)) play important roles in regulating 2'-deoxyuridine, which may be involved in the formation of spiral grains. Meanwhile, the signal transduction of hormones may be related to spiral grain, as previously reported. ARF7 and MKK4_5, as indoleacetic acid (IAA)- and ethylene (ET)-related receptors, may explain the contribution of plant hormones in spiral grain. This study provided useful information on spiral grain in P. yunnanensis by transcriptome and metabolome analyses and could lay the foundation for future molecular breeding.

Ultrasonic pulse velocity for mechanical properties determination of wood

ABSTRACT Wood is a widely used material in various industries, and its mechanical properties are crucial to determine the final product's performance. Modulus of elasticity (MOE) is one of the most important mechanical properties of wood, which measures its stiffness and ability to resist deformation under applied loads. The objective of this research was to create robust models for predicting the moduli of elasticity (MOE) of wood species in three principal directions under varying moisture levels, using the ultrasonic pulse velocity (UPV) technique. The study employed three modeling techniques, namely multivariable linear regression (MLR), artificial neural network (ANN), and support vector regression (SVR). The research involved developing 72 models using different input variables and methods, and then training and testing them with experimental data. Our findings revealed that the SVR model utilizing the radial basis kernel function (RBF) and Levenberg-Marquardt backpropagation ANN exhibited the lowest mean squared error (MSE) and the highest correlation coefficient, with R2 values of 0.979 and 0.989, respectively. These results suggest that the developed models and the UPV technique could significantly enhance the precision of MOE predictions for wood species, presenting a valuable tool for industries that utilize wood in their products.

Size Effect on Hygroscopicity of Waterlogged Archaeological Wood by Simultaneous Dynamic Vapour Sorption

Hygroscopicity is one of the most important properties of wood and plays a decisive role in its dimensional stability. In this context, conservation plans for waterlogged archaeological wood (WAW) and relevant waterlogged artefacts must be created. The size of the sample required for a moisture sorption assessment may affect the results for (and thus the perception of) the hygroscopicity of a testing artefact. Herein, to investigate the effects of the sample size on the hygroscopicity of WAW as measured via dynamic vapour sorption (DVS), typical WAW and recent (i.e., sound) wood are processed into four differently sized samples, ranging in thickness from 200 mesh to millimetre. The equilibrium moisture contents (EMCs) of the wood samples are simultaneously measured using simultaneous DVS. The sorption isotherms show that the EMC values of the recent wood at each relative humidity increase as the sample size decreases, with the superfine powder sample achieving the highest EMC of all of the recent samples. Although the WAW has a higher EMC than that of recent wood, the effect of the size of the WAW sample on its hygroscopic properties is surprisingly not as pronounced as that for the recent wood. In addition, the hysteresis between the samples of different sizes of the archaeological wood is significantly smaller than that for the reference samples. Furthermore, regarding the standard deviations of the parameters obtained from the Guggenheim Anderson de Boer and Hailwood–Horrobin models, the values for WAW are all much smaller than those for the reference wood. This further verifies the disappearance of the size effect of the hygroscopicity for WAW.

Effects of Nanosilver and Heat Treatment on the Pull-Off Strength of Sealer-Clear Finish in Solid Wood Species.

Pull-off strength is an important property of solid wood, influencing the quality of paints and finishes in the modern furniture industry, as well as in historical furniture and for preservation and restoration of heritage objects. The thermal modification and heat treatment of solid wood have been the most used commercial wood modification techniques over the past decades globally. The effects of heat treatment at two mild temperatures (145 and 185 °C) on the pull-off strength of three common solid wood species, i.e., common beech (Fagus sylvatica L.), black poplar (Populus nigra L.), and silver fir (Abies alba Mill.), were studied in the present research work. The specimens were coated with an unpigmented sealer-clear finish based on an organic solvent. The results demonstrated a positive correlation between the density and pull-off strength in the solid wood species. Heat treatment at 145 °C resulted in an increase in the pull-off strength in all three species, due to the formation of new bonds in the cell-wall polymers. Thermal degradation of the polymers at 185 °C weakened the positive effect of the formation of new bonds, resulting in a largely unchanged pull-off strength in comparison with the control specimens. Impregnation with a silver nano-suspension decreased the pull-off strength in beech specimens. It was concluded that density is the decisive factor in determining the pull-off strength, having a significant positive correlation (R-squared value of 0.89). Heat treatment at lower temperatures is recommended, to increase pull-off strength. Higher temperatures can have a decreasing effect on pull-off strength, due to the thermal degradation of cell-wall polymers.

Effects of Pressurized Superheated Steam Treatment on Dimensional Stability and Its Mechanisms in Surface-Compressed Wood

Shape stability is one of the most important properties of surface-compressed wood used as a substitute for other energy-intensive adhesives, concrete, and metals. This study evaluated the dimensional stability, surface wettability, chemical structure, cellulose crystalline structure, and microstructure of surface-compressed wood. The surface-compressed wood was then treated with pressurized superheated steam. The equilibrium moisture content, thickness swelling ratio, and wettability of the wood decreased by 20.39%, 30.63% (moisture absorption), 40.51% (water absorption), and 86.95% after pressurized superheated steam treatment, respectively. In the pressurized steam environment, hemicelluloses were significantly degraded, significantly reducing the strong hygroscopic groups, particularly hydroxyl groups. The crystallinity and crystal width of cellulose in the compressed wood also increased by 8.02% and 37.61%, respectively, after pressurized superheated steam treatment, corresponding to dimensional stability. Dimensional stability, namely the shape fixation of the surface-compressed wood, is a complex mechanism, including the hydrophobization of cell walls, the formation of cross-linkages, the reformation of microfibril chains, microstructural changes, and the relaxation of inner stresses, which reduced or even eliminated the recovery. This study demonstrates that pressurized steam treatment can effectively enhance dimensional stability in surface-compressed wood, which contributes to the substantial use of surface-compressed wood in the building and construction industries. We will further explore the relationship and mechanism between superheated steam pressure, treatment time, and dimensional stability.

Deformation features of cross-glued wooden panel structures for northern construction

Cross-glued wood panels are used in various areas of construction. In recent years, such panels are widely used in multi-storey panel and multi-storey frame construction. The use of panels in multi-storey residential and public construction is based on such an important natural property of wood as dissipativity - the ability to absorb a wide range of dynamic effects, including seismic effects.The structural form of buildings in modern high-rise construction is based mainly on a steel or reinforced concrete frame. High-rise buildings on a frame made of wooden glued elements, with wooden outer and inner panels began to be introduced into the construction practice 15 years ago. To date, residential and public buildings made of wooden cross-glued panels have been built in many countries of Europe and in the USA, Canada, Australia.It can be expected that in high-rise construction, the share of residential and public buildings with the use of wooden glued structures will increase, and will stabilize over time in an objectively justified indicator. The demand for wooden high-rise construction will be determined, among other factors, by the seismicity of the construction areas.

Wood and Pulping Properties Variation of Acacia crassicarpa A.Cunn. ex Benth. and Sampling Strategies for Accurate Phenotyping

Research Highlights: This study provides a comprehensive set of wood and pulping properties of Acacia crassicarpa A.Cunn. ex Benth. to assess variation and efficient sampling strategies for whole-tree level phenotyping. Background and Objectives: A. crassicarpa is an important tree species in Southeast Asia, with limited knowledge about its wood properties. The objective of this study was to characterize important wood properties and pulping performance of improved germplasm of the species. Furthermore, we investigated within-tree patterns of variation and evaluated the efficiency of phenotyping strategies. Materials and Methods: Second-generation progeny trials were studied, where forty 50-month-old trees were selected for destructive sampling and assessed for wood density, kraft pulp yield, α-cellulose, carbohydrate composition, and lignin content and composition (S/G ratio). We estimated the phenotypic correlations among traits determined within-tree longitudinal variation and its importance for whole-tree level phenotyping. Results: The mean whole-tree disc basic density was 481 kg/m3, and the screened kraft pulp yield was 53.8%. The reliabilities of each sampling position to predict whole-tree properties varied with different traits. For basic density, pulp yield, and glucose content, the ground-level sampling could reliably predict the whole-tree property. With near infrared reflectance spectroscopy predictions as an indirect measurement method for disc basic density, we verified reduced reliability values for breast height sampling but sufficiently correlated to allow accurate ranking and efficient selection of genotypes in a breeding program context. Conclusions: We demonstrated the quality of A. crassicarpa as a wood source for the pulping industry. The wood and pulping traits have high levels of phenotypic variation, and standing tree sampling strategies can be performed for both ranking and high-accuracy phenotyping purposes.

Relationship between pore structure and gas permeability in poplar (Populus deltoides CL.\u201955/65\u2019) tension wood

Key messageThe important anatomical changes in tension wood, e.g., the high fiber ratio and rich mesopores, did not significantly increase the air and nitrogen flow; thus the gas permeability in the longitudinal direction of poplar (Populus deltoidesCL.’55/65′) tension wood is actually affected by the cell tissue macroporous porosity.ContextGas permeability is one of the most important physical properties of wood and is closely related to its internal microstructure, particularly porosity. Tension wood is widespread in woody plants and displays significant structural differences compared with opposite wood.AimsThe study was designed to clarify the relationship between pore structure and gas permeability in poplar tension wood.MethodsThe gas permeability was measured using a self-made device. The meso- and macroporosity characteristics were measured by nitrogen adsorption–desorption and mercury intrusion porosimetry. The flow was simulated using ANSYS Fluent software to illustrate the role of pore structure on permeability.ResultsThe morphological features of vessels have an effect on wood permeability. Compared with tension wood, opposite wood, which has higher vessel ratio, larger cell lumen diameter, and more rich pits, shows stronger gas permeability. Increasing the airflow path will actually reduce the gas permeability. The simulation results are consistent with the experimental results.ConclusionIn hardwoods, the gas permeability in the longitudinal direction is mainly dictated by the vessels. The high fiber ratio and rich mesopore in tension wood do not significantly increase gas flow, suggesting the permeability of wood was actually determined by the cell tissue with macroporous porosity. Vessel tissue ratio, length and diameter, and intervessel pit size were found responsible for influencing the permeability in the longitudinal direction.

Modelling variation in wood stiffness of Pinus ponderosa using static bending and acoustic measurements

Abstract Wood removed in Southwestern US forest restoration treatments currently has limited markets and thus low value. One important property of wood in structural products is its stiffness (measured as modulus of elasticity), which is known to vary systematically within trees. Directly measuring wood stiffness is expensive, time consuming and destructive. Therefore, we tested samples of ponderosa pine (Pinus ponderosa var. scopulorum Engelm.) from northern Arizona destructively in bending and also non-destructively using acoustic velocity (AV) methods. In total, we tested multiple pith-to-bark small clear (2.54 × 2.54 × 40.64 cm) samples from up to four heights in 103 trees. We first measured the standing-tree AV of sample trees, then the AV of small clear samples, and finally measured wood stiffness using three point static bending tests. We found that a Michaelis–Menten curve was a good fit to the radial profile of wood stiffness, with a steep increase outward from the pith that approached an asymptote. The AV of small clear samples, coupled with measured volumetric density values, approximated the static modulus of elasticity values with high accuracy (r2 = 0.86). At the stand level, a model predicting standing tree AV from tree morphology fit the data well (r2 = 0.77). Results indicate that southwestern ponderosa pine contains outerwood with relatively high stiffness that could be suitable for structural products. However, when assessed using wood stiffness, the trees take a long time to reach maturity (~50 years) and thus the corewood proportion is large. AV measurements are a good way to assess variability within and among stands and thus could be employed to segregate the resource by expected stiffness values. Segregation could help identify stands not suitable for structural uses and direct them toward more appropriate products.

Thermochemical and Mechanical Properties of Pine Wood Treated by In Situ Polymerization of Methyl Methacrylate (MMA)

The impregnation of low-molecular-weight monomers prior to polymerize them inside the wood may be an efficient way to improve some important wood properties. This work aimed to determine some technological properties of wood-based composites (WPC) produced by in situ polymerization, using a pine wood (Pinus elliottii Engelm.) impregnated with methyl methacrylate (MMA). For that, samples taken from both juvenile (JV) and mature (MT) pine woods were treated with MMA. Physical, mechanical, chemical, thermal and morphological features were evaluated. MMA-treated woods from both juvenile and mature woods presented superior physical, mechanical (expect brittleness) and thermal properties when compared to pristine ones. The infrared spectra and morphological analysis by scanning electron microscopy (SEM) confirmed the presence of the monomer inside the pine wood. The juvenile wood presented higher treatability than the mature wood, due to its higher content of intra- and inter-cellular spaces.

Estimating wood moisture by near infrared spectroscopy: Testing acquisition methods and wood surfaces qualities

ABSTRACT Moisture is one of the most important wood properties because its variation directly influences the material strength and density. Thus, the aim of this study was to develop near infrared (NIR) spectroscopic models in order to estimate the moisture content in wood specimens. Moreover, predictive models built from NIR signatures recorded by different acquisition methods and on wood surfaces were compared and discussed. Mass and NIR spectra were measured on forty (40) Eucalyptus wood specimens in 10 steps during drying from the fiber saturated point to anhydrous condition. NIR spectra were recorded by means of an integrating sphere and optical fiber probe on four surface. Thus, wood moisture values were correlated with the corresponding NIR spectra by Partial Least Squares (PLS) Regression. The best models for estimating wood moisture were developed from NIR spectra recorded on the transverse surface produced with the band saw by integrating sphere method (R²p = 0.96 and RMSEP = 8.56%) and fiber optic probe (R²p = 0.83 and RMSEP = 20.09%). Therefore, NIR spectrum recorded by integrating sphere taken on transverse or radial wood surface cut by band saw are the most suitable for generating NIR models for estimating the moisture content in Eucalyptus wood.

Predicting Density and Moisture Content of Populus xiangchengensis and Phyllostachys edulis using the X-Ray Computed Tomography Technique

Abstract Density (D) and moisture content (MC) are two important physical properties of wood and bamboo, which are highly correlated with many other physical and mechanical properties. In this study, the X-ray computed tomography (CT) technique was used to determine the D and MC of poplar (Populus xiangchengensis) and bamboo (Phyllostachys edulis). There was a statistically significant difference in the CT-measured numbers for D and MC between these species. The D-CT and MC-CT linear models for both species were independently established: Dpoplar = 0.00098 × H + 1.02603, Dbamboo = 0.00118 × H + 0.98684, MCpoplar = 0.00309 × H + 1.89982, and MCbamboo = 0.00131 × H + 0.31488, where H is the CT number. The determination coefficients, R2, of the models were all higher than 0.97. Additionally, the R2 values obtained for model validation were also all higher than 0.97. These results indicated that it is feasible to reliably determine D and MC of wood and bamboo using the X-ray CT technique. This study aims to provide reference data for CT detection of the D and MC of wood and bamboo.

Radial permeability of the hybrid pine (Pinus elliottii × Pinus caribaea) in Australia

The radial permeability (gas and liquid) of the hybrid pine (Pinus elliottii var. elliottii [PEE] × Pinus caribaea var. hondurensis [PCH]) was investigated for wood samples collected from 30 trees that were 19 years of age and represented various genotypes and stocking rates. The PEE × PCH hybrid is now a very important resource for the Australian forestry industry, producing logs used to manufacture a diverse array of wood products. The permeability of wood influences many important wood properties and industrial processes. For all data combined from all radial sampling positions, there was no significant effect of genotype and stocking rate on radial permeability. Both gas and liquid permeability increased from pith to bark positions within the tree. Conversely, resin content decreased from pith to bark positions. Gas and liquid permeability were significantly positively correlated, and a highly significant negative relationship was also found between permeability (gas and liquid) and resin content.

Uticaj različitog sadržaja vlage na termalna svojstva drva

Moisture content is one of the most important properties of wood. The primary purpose of this paper is to examine the dependence between thermal properties and different moisture contents of softwood, hardwood and medium hardwood samples with dimensions of 100 x 100 mm and a thickness of 10 mm (measured using the transient method). Different moisture contents of the wood samples under consideration were achieved by a gradual drying treatment in the laboratory setting. The final results obtained represent the arithmetic means computed from ten sets of measurements. The measured relationship between the thermal conductivity and the mass specific heat of the wood samples was found to indicate an increasing trend, whereas the relationship between the thermal diffusivity and the moisture content of the wood samples showed a non-linear decreasing trend. On the basis of the results obtained, it can be concluded that the thermal properties of wood are greatly affected by the type of wood and changes in the wood moisture content, which mainly depend on wood structure and water conduction in wood.

Variação radial e longitudinal da densidade básica da madeira de Pinus patula

A densidade básica da madeira é considerada uma das propriedades mais importantes, pois influencia diretamente as demais características físicas para a utilização industrial. O presente estudo teve como objetivo determinar a densidade básica média da madeira de árvores de Pinus patula Schltdl & Cham. e analisar a sua variação nos sentidos radial e longitudinal. As amostras foram retiradas de 12 árvores com 9 anos de idade, ao longo dos eixos longitudinal e radial. A densidade básica média observada foi 0,307 g cm-³. Observou-se aumento da densidade básica no sentido medula-casca e decréscimo no sentido longitudinal apenas da base até 2 m. Foi verificada interação entre as variações nos sentidos radial e longitudinal da madeira, indicando que a densidade da madeira de P. patula varia nos diferentes sentidos de crescimento..

Microstructural characterization and evaluation of certain important physical properties of thuja burl wood

This investigation aimed to characterize certain important anatomical, chemical and physical properties of Tetraclinis articulate (Thuja) burl wood from Morocco. Anatomical properties and constituent structure were analysed using image analysis system, environmental scanning electron microscope (ESEM) and powder x-ray diffraction techniques. A few important physical properties of Thuja burl wood such as density, specific gravity, equilibrium moisture content (EMC), total swelling and water absorption characteristics were evaluated. Real-time water absorption and swelling profiles were recorded electronically using a digital force sensor and linear variable differential transformers (LVDTs) respectively. Microscopic structure observed on fractured surfaces showed very compact and thread-like fibers. Average crystallinity index and diameter of cellulose crystallite was found to be 0.35±0.03 and 36.00±5.58 A respectively. The average values of air-dry density and the EMC of Thuja burl wood were 932.67±50.57 kg/m3 and 10.19±1.43% respectively. Swelling profile as a function of the water immersion duration followed a curvilinear variation with maximum swelling coefficient of 2.9±0.43% after 24 hour from oven-dry condition. The suitability of this wood for decorative and handicraft items is attributed mainly to its dense microstructure, higher dimensional stability, lower water absorption, random grain texture, dark brownish with intense and pleasant smell.

Charring rates of timbers from Chinese species and comparison with various charring rate models

The charring rate is the most important property of wood with respect to its fire resistance and fire integrity. It is necessary to predict the charring rate of wood through a charring rate model due to the difference of various test methods and the variety of wood species. A power integral charring rate model, the CAF model, has been developed based on Chinese species using the cone calorimeter. Theoretical charring rate results of CAF model, EC5 model, Australian code AS 1720.4 and Ulg model were calculated from experimental details by Njankouo et al. (Constr Build Mater 19(5):376–386, 2005) and Cachim and Franssen (Fire Mater 33(3):129–143, 2009), respectively. Then, these theoretical charring rate results were again compared with tested charring rate results from Njankouo et al. (Constr Build Mater 19(5):376–386, 2005) and Cachim and Franssen (Fire Mater 33(3):129–143, 2009). The results showed that the cone calorimeter can be equal to the furnace for studying wood charring when the heat flux is considered. The precision of the power integral model is higher with the increase in burning time. The EC5 model, Australian code AS 1720.4, Ulg model and White’s model are not entirely satisfactory. The power integral model is acceptable for medium density as well as high density, while unsafe at a density of less than 290 kg/m3.

Probabilistic sensitivity analysis to understand the influence of micromechanical properties of wood on its macroscopic response

This paper investigates the influence of the uncertainty in different micromechanical properties on the variability of the macroscopic response of cross-laminated timber plates, by means of a probabilistic sensitivity analysis. Cross-laminated timber plates can be modelled using a multiscale finite element approach which although suitable, suffers from high computational cost. Investigating parametric importance can incur considerable time penalty since conventional sensitivity analysis relies on a large number of code evaluations to produce accurate results. In order to address this issue, we build a statistical approximation to the code output and use it to perform sensitivity analysis. We investigate the effect of a collection of parameters on the density and Young’s moduli of wood. Additionally, the influence on the response of cross-laminated timber plates subject to bending, in-plane shear and compression loads is investigated due to its relevance within the engineering community. The presented results provide a practical insight into the importance of each micromechanical parameter, which allows research effort to be focused on important wood properties.

Influence of Heat Treatment on the Water Uptake Behavior of Wood

Dimensional stability is an important property of wood that is strongly influenced by its water uptake behavior. Heat treatment is one method to improve wood dimensional stability. This study investigated the effects of heat treatment on the water uptake behavior of wood using a wicking test. The thickness of the tested wood sample was similar to that of the surface wood panel in a 3-layer composite floorboard. It was treated at different temperatures ranging from 200 °C to 400 °C under a nitrogen atmosphere for 10 min to provide the test data to investigate the basic theory relating to dimensional stability of heat-treated wood processed at higher temperatures for a short length of time. During the test, the water uptake of larch (Larix gmelinii) and red oak (Quercus rubra) were recorded continuously. The heat-treated wood had a much lower water uptake ability than untreated wood during the early stage of the wicking test; untreated wood exhibited higher total water uptake. Compared with the untreated sample, the red oak wood treated at 400 °C had an average water uptake rate that decreased from 0.28 mg/mm3 per hour to 0.038 mg/mm3 per hour.