Volume 73, Issue 9

The use of acoustic velocity for different purposes is becoming widespread in the forestry industry. However, there are conflicting reports on how well this technology reflects the mechanical properties of trees. In this study, the prediction of timber quality using acoustic technology was evaluated on mature standing trees of three softwood species. The velocity in 490 standing trees was measured in several directions (longitudinal, radial and tangential). A sub-sample of trees was felled and the acoustic velocity was measured in 120 logs which were then sawn into structural-sized timber. A total of 1383 boards were tested for bending, as were small clear specimens extracted from the structural-sized boards. The mean tree values of the timber grade-determining properties (elastic modulus, bending strength and density) of both specimen sizes were related to the acoustic velocities and tree slenderness. The correlations between the mean tree mechanical properties and acoustic velocities were relatively low, most likely due to a high ratio of diameter to measurement distance. The transverse directions showed similar correlations with mechanical properties in larger-diameter trees to the longitudinal direction, as did tree slenderness. The results suggest that while the acoustic velocity in the longitudinal direction can reflect the mean tree mechanical properties in small-diameter trees, alternatives are needed to achieve the same in larger-diameter trees.

Field measurements were carried out to assess the feasibility of ultrasound velocity and damping for the non-invasive testing of standing trees. A total of 87 trees of European beech ( Fagus sylvatica L.) and 68 trees of Norway spruce ( Picea abies Karst.) were measured in the field, felled and assessed individually for the presence of red heartwood or butt rot. The field assessment of these internal structural defects at the stump level (SL) of the trees was compared with the ultrasound measurements recorded at two tree heights [(i.e. at the SL and 0.5 m above the stump level (ASL)] and in several directions, all perpendicular (PP) to the tree stem. Lower ultrasound velocity and higher damping were found in both species with the presence of internal defects in both the radial and tangential directions of the tree stem. The diameter at breast height (DBH) had a varying effect on both ultrasound velocity and damping. A binary logistic regression was used to test the potential of ultrasound velocity and damping to predict the presence of internal defects. Both the approaches offer similar levels of prediction accuracy (0.72 and 0.76 in beech, and 0.83 and 0.82 in spruce). Due to the significant reduction in measuring time when using ultrasound damping only, this principle is recommended for the detection of red heartwood in beech trees and butt rot in spruce trees.

As the strength of wood is greatly affected by its three-dimensional (3D) grain angles (the dive angle and the surface angle), the wood industry today requires automatic, rapid, and robust measurement techniques for measuring them simultaneously. In the present study, a near infrared spatially and spectrally resolved imaging (NIR-SSRI) system was designed in a line scan model, mainly including an NIR hyperspectral imaging camera and a halogen spotlight source (Ø 1 mm). Spatially resolved diffuse reflectance images at three target wavelengths (1002 nm, 1217 nm, and 1413 nm) were obtained from Hinoki cypress [ Chamaecyparis obtusa (Siebold & Zucc.) Endl.] samples at various (0°, 3°, 6°, … 45°) dive angles and surface angles (0°, 3°, 6°, … 45°). The scattering patterns caused by the “tracheid effect” were almost elliptical. Subsequently, nonlinear least squares fitting was used to determine their eccentricities ( e ) and rotation angles ( θ ). The e values at each selected wavelength were highly correlated with the dive angle reference values; and the global identification model developed using Gaussian process regression (GPR) under five-fold cross-validation (CV) reached a determination coefficient ( r 2 ) of 0.98 with a root mean square error (RMSE) of 2.2°. On the other hand, local surface angle identification models developed using linear regression analysis achieved determination coefficients higher than 0.90 on r 2 and an RMSE of CV lower than 3.8° when the dive angle was lower than 30°.

This study investigated using the stress wave method to predict the properties of thermally modified wood by means of an adaptive neuro-fuzzy inference system (ANFIS) and neural network (NN) modeling. The stress wave was detected using a pair of accelerometers and an acoustic emission (AE) sensor, and the effect of heat treatment (HT) on the physical and mechanical properties of wood as well as wave velocity and AE signal is discussed. The AE signal was processed in the time and time-frequency domains using wavelet analysis and different features were extracted for network training. The auto-associative NN is used as a dimensional reduction method to decrease the dimension of the extracted AE features and enhance the ANFIS performance. It was shown that while the stress wave velocity using the accelerometer did not result in an accurate model, the network performance significantly increased when trained with the AE features. The AE signal exhibited a significant correlation with wood treatment and porosity. The best ANFIS performance corresponded to predicting the wood swelling coefficient, equilibrium moisture content (EMC) and water absorption (WA), respectively. However, the AE signal did not seem suitable for predicting the wood density and hardness. The performance of ANFIS was compared with the “group method of data handling” (GMDH) NN. Both the ANFIS and GMDH networks showed higher accuracy than the multivariate linear regression (MVLR) model.

The objective of this research was to evaluate the influence of acetyl and methyl bonds on the physical, mechanical, photochemical and biological resistance properties of hornbeam wood. Carpinus betulus (hornbeam) wood is considered to be a less valuable species due to poor durability. In order to improve its properties, a novel and simple method was applied to modify wood samples. Hence, wood samples were modified by either acetylation or methylation at four treatment levels. Reactions between hornbeam wood and the formalin and acetic acid treatment system were successful as exemplified by increased mass [weight percent gain (WPG)], slightly better compression strength and considerably improved impact bending strength. Furthermore, the biological decay resistance of the treated wood samples increased for all of the treatments.

In this study, in situ graft polymerization of ε-caprolactone (CL) was studied for its potential to limit boric acid (BA) leaching from wood, and to increase the dimensional stability and biological durability of wood against Coniophora puteana and Trametes versicolor fungi. For this purpose, CL monomer with/without BA was impregnated into wood, and the monomer was polymerized in wood cell walls using various methods and combinations of reactants. It was found that biodegradable polycaprolactone (PCL) grafting at high monomer concentrations could inhibit fungal degradation of wood cell walls, as well as improve the dimensional stability of wood up to 55% and reduce water uptake (WU) by about 50%. However, inductively coupled plasma-optical emission spectrometry (ICP-OES) analysis revealed that in situ graft polymerization of CL is not an effective method to prevent BA leaching from wood.

The anatomical characteristics of oak wood, which is usually employed for making wine barrels, affect the properties of the wine, because these characteristics are related to the chemical compounds that can be potentially transferred to wine during the aging process. Grain, as the rate of tree growth, is the most commonly employed parameter to define the quality of the oak wood used in cooperage. Nevertheless, oxygen is a key factor in this process and there are few articles that evaluate the oxygen transmission rate (OTR) of the wood employed in cooperage. This work presents the evaluation of the anatomical characteristics of the French oak ( Quercus petraea Liebl.) measured with X-ray computed tomography and the OTR of 267 wood samples extracted from recently constructed wine barrels. This study demonstrates that the OTR is dependent on the anatomical features of oak wood, the first step to classify a natural material as wood for custom oxygenation barrel making. OTR cannot be determined from the wood grain or any other single property because it depends on the overall anatomical characteristics of each wood sample, the grain and the average earlywood and latewood width being the three parameters with a stronger correlation with the OTR.

Waterborne coatings are widely used for environmental protection. However, they lead to many defects and lower the mechanical properties when applied to wood surfaces. To address this challenge, the effects of multilayer waterborne polycrylic coatings on the mechanical properties of southern pine cell walls were investigated by nanoindentation. The experimental results indicated that the coating layers significantly reduced the elastic modulus ( E r ) and hardness ( H ) values than the wood cell walls. The E r and H values measured along the coating layer thickness direction increased significantly as the distance of the indents to the wood surface decreased. Intact cell walls adjacent to or away from the coating layers had higher E r and H values than partial ones. This study will also be useful in helping to understand the bonding mechanism at the interface between coatings and wood cell walls.

In order to increase the curing rate of polymeric diphenylmethane diisocyanate (PMDI) resin, different contents of lignin-containing cellulose nanofibrils (L-CNFs) were blended into the PMDI. Differential scanning calorimetry (DSC) was used to examine how the addition of L-CNFs influences the curing kinetics of PMDI resin. The activation energy ( E a ) of the curing reaction of PMDI/L-CNF systems was calculated using the Kissinger, Friedman and Flynn-Wall-Ozawa model-free methods. The results showed that E a values calculated by the aforementioned three methods varied in a similar trend with the increase in the L-CNF content. Adding L-CNFs could decrease the E a value of the curing reaction of PMDI and speed up the curing reaction. The acceleration of the cure rate of the PMDI resin upon the addition of L-CNFs may be attributable to the effective dispersion of the L-CNFs into the PMDI resin as well as the reaction between the hydroxyl (-OH) groups of the L-CNFs and the isocyanate (-NCO) groups of the PMDI.