Volume 75, Issue 12

Acacia, including Acacia hybrids, are some of the most important species grown as part of the Vietnamese wood industry. Rapid methods to identify the variations in the wood properties of Acacia hybrids however, are a currently lacking and creating limits for their breeding programs. In this study, nine Acacia hybrid clones, including those that were diploid, triploid, and tetraploid were evaluated using near-infrared spectroscopy (NIR) and hyperspectral imaging (HSI). The standard normal variate (SNV) and second derivative (SP2D) were applied to compare the performances of NIR and HSI using partial least square regression. The HSI images were acquired at wavelengths from 1033 to 2230 nm and the SNV and SP2D described the variations in the wood properties. The NIR predicted the wood physical properties better than HSI, while they provided similar predictions for the mechanical properties. The mapping results showed low densities around the pith area and high densities near the bark. They also revealed that the air-dry moisture content changed at different positions within a disk and was dependent on its position within the tree. Overall, NIR and HSI were found to be potential wood property prediction tools, suitable for use in tree improvement programs.

The study of moisture migration in Norway Spruce may reduce the discrepancy between measurements and simulations of transfers in buildings and thus be helpful for improving their performance and durability. For this purpose, X-ray imaging was used to study moisture migration in Norway spruce during imbibition at tissue level. Moisture content kinetics in earlywood and latewood, based on X-ray attenuation, was observed and measured through rigorous protocol. The imbibition process was studied in both longitudinal and radial directions. The results showed an easier migration of liquid in latewood than in earlywood in the longitudinal uptake. In the radial direction, the impact of compression wood as a barrier and the role of the anatomical structure in the liquid migration were highlighted by the direct visualization of filled tracheids.

The non-destructive wave propagation technique is used to estimate the wood’s modulus of elasticity. The propagation speed of ultrasonic waves is influenced by some factors, among them: the type of transducer used in the test, the form of coupling and the sensitivity of the transducers. The objective of the study was to evaluate the influence of the contact pressure of the transducers on the ultrasonic speed. Ninety-eight tests were carried out on specimens of the species Eucalyptus grandis , with dimensions of 120 × 120 × 50 mm. The calibration of the pressure exerted by the transducer was controlled by a pressure gauge using a previously calibrated load cell. The robust statistical analysis allowed to validate the experimental results and to obtain consistent conclusions. The results showed that the wave propagation speed is not influenced by the pressure exerted by the transducer.

Oak wood is popular for use in construction and as flooring. Evaluating the mechanical strength of oak timber is difficult and time consuming. Therefore, models for predicting mechanical properties, based on easy-to-obtain variables, may be useful. The purpose of the study was to build models for predicting shear strength parallel-to-grain in oak clear wood. With this goal, the shearing resistance was tested on 198 defect-free specimens (target dimensions 50 × 50 mm in tested section) obtained from a sample of 40 oak trees felled in north-western Spain. The mean shear strength of the sampled oak wood provenance was 15 N mm −2 , which was almost equal to the highest mean value reported in previous studies. Analysis of the relationships between the variables tested enabled development of a model relating shear strength parallel to grain at 12% moisture content, with air-dry wood density and angle between tangential and shear plane as predictor variables ( R adj 2 ${R}_{\text{adj}}^{2}$  = 0.61, p  < 0.01, bias = −0.80%, RMSE  = 13.66%, for wood with wavy grain; R adj 2 ${R}_{\text{adj}}^{2}$  = 0.36, p  < 0.01, bias = −1.46%, RMSE  = 17.22%, for wood without wavy grain). The independence of shear strength relative to the presence/absence of sapwood or the annual growth ring width was also demonstrated.

In this study, the sound absorption coefficient of three low density hardwoods – binuang, balsa and paulownia – were investigated. Their gas permeability and pore size were measured, and their pore shapes were classified into through pore, blind pored, and closed pore, as specified by the International Union of Pure and Applied Chemistry (IUPAC). Among the three species, obvious that paulownia had lowest sound absorption when the two of others showed higher sound absorption. Although paulownia is a high porosity wood, most of its vessels are blocked by tyloses; it is therefore difficult for sound waves to enter its pores, which results in poor sound absorption performance. This study showed that the higher the through pore porosity, the higher was the gas permeability, which led to improvement of the sound absorption performance. It was also found that the sound absorption coefficient of the three species woods increased at low frequencies as the size of an air cavity between the specimens and tube’s wall increased.

The thermal insulation properties of bark and wood of a poplar tree ( Populus nigra  ×  alba ) were investigated using a guarded hot plate device (GHP) and a purpose-built miniature heat flow meter (Mini-HFM). To reduce their density and improve their performance as insulation material, bark and wood were chemically treated. The correlation between thermal conductivity and test temperature as well as between thermal conductivity and material moisture was investigated. By means of the treatment 44 and 34% of the mass of bark and wood, respectively, was removed and the equilibrium moisture content of the both materials decreased significantly. For untreated bark, a thermal conductivity of 0.071 Wm −1  K −1 and 0.140 Wm −1  K −1 , respectively, were determined in transverse and axial direction. For wood, measurements showed comparably higher conductivities of 0.078 Wm −1  K −1 and 0.204 Wm −1  K −1 in transverse and axial direction. By reducing density, thermal conductivity of bark decreased up to 24%, whereas for wood reductions between 10 and 35% were found. It was shown that the self-constructed Mini-HFM is a useful and reliable instrument to determine the thermal conductivity on a small wood sample in the three main anatomical directions.

Citric acid together with sorbitol (SorCA) have been used to modify wood and improve its properties, such as dimensional stability and biological durability, which partly result from its swelling and sorption behavior. However, the underlying mechanism of water interaction with SorCA-treated wood is very complex and not fully understood. Previous research confirmed cell wall bulking and suggested cross-linking, however the extent of their contribution to moisture-induced changes has not been researched. This study investigated the effect of SorCA treatment on sorption properties of wood in the hygroscopic range (0–95% RH). Scots pine sapwood ( Pinus sylvestris L.) was chemically modified with an aqueous SorCA solution at different treatment levels and measured by dynamic vapor sorption (DVS). The observed permanent increase in oven-dry dimensions did not result in a decreased swelling compared to untreated specimens. It was ascribed to the excessive expansion of cell wall matrix caused by a degradation of cell wall constituents by the acidic impregnation solution. However, a reduction in moisture content in comparison to untreated reference was detected. Present findings suggest that the SorCA polyester structure is altered after impregnation inside the wood and affects its sorption behavior by covalent bonding and, presumably, cross-linking with wood polymer constituents.

Wood properties of furfurylation can be altered by reaction mechanisms of furfuryl alcohol polymer (PFA) and cell walls. Although chemical reactions between PFA and lignin have been studied, reaction mechanisms between PFA and cell wall components, including lignin, cellulose and hemicellulose are still not comprehensively understood. In order to elucidate chemical reactions regarding PFA with wood cell walls, model compounds of main cell wall components were used to investigate its reactions with PFA by 13 C NMR spectroscopy and differential scanning calorimetry (DSC). Results showed that there was no chemical bonding of PFA with either cellulose or hemicellulose. Condensations of uncrowded ring positions ( meta, ortho and para ) and side chains (α–C, β–C, β–OH, and γ–OH) of lignin with PFA did occur based on 13 C NMR spectra. Reaction enthalpy and activation energy also confirmed the condensation reactions between lignin and PFA. This study could provide design guidelines to control the chemical reactions of PFA in cell walls and lignin and, therefore, improve the properties of furfurylated wood.