Roger E. Hernández

A NMR study of water distribution in hardwoods at several equilibrium moisture contents

The water state of one tropical (Robinia coccinea) and two temperate (Acer saccharum and Fagus grandifolia) hardwoods was determined at different equilibrium moisture contents (EMC) during desorption at 25°C. NMR technique was used to separate different components of water in wood. The species studied presented different structures, which were apparent on the spin–spin relaxation T2 values. Three different water components were separated: slow T2 (liquid water in vessel elements), medium T2 (liquid water in fiber and parenchyma elements) and fast T2 (bound or cell wall water). The NMR results showed that even at equilibrated conditions a region exists where loss of liquid water and bound water takes place simultaneously. This region will vary according to the wood structure. Finally, liquid water was present at EMC lower than the fiber saturation point, which contradicts the concept of this point when considered as a bulk property of wood.

Changes in physical properties of tropical and temperate hardwoods below and above the fiber saturation point

Changes in physical and mechanical properties of wood were analyzed using sorption tests combined with dimensional measurements and perpendicular-to-the-grain tangential compression tests. In order to determine the influence of wood structure on these changes, three hardwood species (Fagus grandifolia, Brosimum alicastrum and Cariniana domestica) presenting different anatomical structures were studied. Two experimental techniques were used to perform moisture sorption tests at 25°C. The first technique used saturated salt solutions (from 33 to 90% relative humidity) and the second used the pressure membrane method (above 96% relative humidity). Special attention was given to the “fiber saturation region”, where changes in wood properties started to take place. Results showed that at equilibrium moisture content (EMC), radial, tangential and volumetric shrinkage, as well as changes in transverse strength occurred above the fiber saturation point (FSP). This behavior can be explained by the effect of hysteresis at saturation on wood properties. This hysteresis indicates that loss of bound water takes place in the presence of liquid or capillary water, which contradicts the concept of FSP. The initial EMC at which bound water starts to be removed varied largely among the wood species.

Effects of abrasive mineral, grit size and feed speed on the quality of sanded surfaces of sugar maple wood

Sanding is a common practice required in order to prepare wood surfaces for coating. Little literature is available regarding the effect of sanding parameters on the quality of surfaces. Sugar maple wood surfaces were evaluated in samples that had been sanded using two types of abrasive minerals, three grit sizes and four feed speeds. Roughness, wetting properties and cell damage were used to assess surface quality. Both abrasives decreased roughness and cell damage from 100- to 120-grit sanding stage. Addition of a 150-grit stage did not further reduce the roughness, whereas the cell damage continued to decrease. Increasing feed speed led to rougher surfaces due to higher fibrillation. Surfaces produced by silicon carbide were smoother and less damaged than those obtained with aluminum oxide. However, the surfaces sanded with aluminum oxide were more wettable and showed no significant difference in wetting time as a function of grit size. For these surfaces, the wetting time was reduced as feed speed increased.

Identification of internal defect of sugar maple logs from CT images using supervised classification methods

Sugar maple logs (Acer saccharum Marsh.) were scanned using X-ray medical scanner in order to develop a classification procedure for this type of imagery (CT images). The classification procedure was required in order to separate sapwood from colored heartwood, knots, rot and bark. Five logs coming from a freshly cut tree (group 1) and three logs sampled from a sawmill yard (group 2) were chosen for this purpose. Two parametric supervised classification algorithms, a minimum distance (MDC) and maximum likelihood (MLC) ones, were qualitatively and quantitatively tested and the resulting thematic maps were filtered by a 5×5 median filter. The classification accuracy was evaluated with confusion matrix and Kappa analyses. Sapwood is known to be the key factor determining sugar maple lumber value. The sapwood identification accuracy was found to be 98.6% (MDC) and 97.2% (MLC) for group 1 and 80.7% (MDC) and 81.8% (MLC) for group 2, respectively. Misclassification of defects occurred mainly between knots and colored heartwood. The overall accuracy of classification was about 83.1% (MDC) and 82.6% (MLC) for group 1 and 76.4 (MDC) and 78.0% (MLC) for group 2, respectively. The Kappa value from MDC and MLC was 0.622 and 0.624 for group 1 and 0.440 and 0.470 for group 2, respectively. These Kappa values indicate the existence of strong and moderate degree of conformity between the reference data and the classification procedure for groups 1 and 2 of logs, respectively. Both classifiers show no statistically significant differences in their capability of separation of sapwood from the other classes. Nevertheless, as MLC accuracy for colored heartwood is higher than MDC accuracy in logs without bark (normal situation in sawmills), MLC appears at this stage as the better alternative for analysing CT images of sugar maple logs. ZusammenfassungAm Beispiel von Zuckerahorn-Stammabschnitten (Acer saccarum Marsh.), die mit einem Computertomographen gescannt wurden, wurde ein Auswerteverfahren für die CT-Bilder entwickelt. Dieses Verfahren war erforderlich, um Splintholz von Farbkernholz, Ästen, Fäule und Rinde unterscheiden zu können. Dazu wurden fünf Stammabschnitte von frisch gefällten Bäumen (Gruppe 1) und drei Stammabschnitte aus einem Sägewerk (Gruppe 2) entnommen. Zwei vorwissensbasierte Auswerteverfahren, Minimum Distance (MDC) und Maximum-Likelihood (MLC), wurden sowohl qualitativ als auch quantitativ getestet. Die daraus resultierenden thematischen Karten wurden mit einem 5×5 Medianfilter gefiltert. Die Auswertegenauigkeit wurde anhand einer Konfusionsmatrix und mittels Kappa-Analysen bewertet. Splintholz ist der entscheidende Faktor, der den Wert von Zuckerahorn-Schnittholz bestimmt. Splintholz konnte in der Gruppe 1 mit einer Genauigkeit von 98.6% (MDC) und 97.2% (MLC) und in der Gruppe 2 mit 80.7% (MDC) und 81.8% (MLC) erkannt werden. Auswertefehler ergaben sich hauptsächlich bei der Unterscheidung zwischen Ästen und Farbkernholz. Insgesamt lag die Auswertegenauigkeit in der Gruppe 1 bei 83.1% (MDC) und 82.6% (MLC) und in der Gruppe 2 bei 76.4% (MDC) und 78.0% (MLC). Der Kappa-Wert von MDC und MLC lag in der Gruppe 1 bei 0.622 und 0.624 bzw. in der Gruppe 2 bei 0.440 und 0.470. Diese Kappa-Werte weisen auf einen hohen bzw. mittleren Übereinstimmungsgrad zwischen den Referenz- und den Auswertedaten für Stammabschnitte der Gruppen 1 bzw. 2 hin. Beide Verfahren unterscheiden sich statistisch nicht signifikant bezüglich ihrer Fähigkeit, Splintholz von den anderen Holzmerkmalen zu trennen. Dennoch erscheint zum gegenwärtigen Zeitpunkt MLC die bessere Alternative zur Auswertung von CT-Bildern von Zuckerahorn-Stammabschnitten zu sein, da MLC Farbkernholz in Stammabschnitten ohne Rinde (Normalsituation in Sägewerken) mit höherer Genauigkeit identifiziert als MOC.

Influence of moisture sorption history on the swelling of sugar maple wood and some tropical hardwoods

SummarySamples of nine tropical hardwoods from Peru and sugar maple wood from Quebec were selected to perform moisture sorption tests associated with swelling tests at 25 °C. The results demonstrate that, for a given equilibrium moisture content, tangential and radial dimensions, and hence the volume of wood, are greater after desorption than after adsorption. The importance of these differences, so-called second-order effects of moisture sorption, varied with the species and with the direction of swelling. These effects are proportionally greater in the tangential direction of wood than in its radial axis. Finally, two types of samples showed similar swellings for three equilibrium moisture contents.

Improving the Sanding Process of Black Spruce Wood for Surface Quality and Water-Based Coating Adhesion

The sanding of black spruce wood prior to coating application was optimized for feed speed and grit size. As feed speed increased, the surface roughness and the surface energy of the samples increa...

Influence of accessory substances, wood density and interlocked grain on the compressive properties of hardwoods

Wood samples of nine tropical hardwoods from Peru and sugar maple wood from Quebec were selected to perform moisture sorption tests associated with parallel-to-grain and tangential compression tests using a multiple step procedure at 25°C. Cold-water and hot-water extractives, sequential cyclohexane (CYC), acetone (ACE) and methanol (MET) extracts, ash content (ASH), wood density and interlocked grain (IG) were evaluated on matched samples too. Wood density corrected for the accessory substances was by far the major factor positively affecting the compressive properties of tropical hardwoods. The total amount of accessory substances is required in order to establish better relationships between physico–mechanical properties and density of tropical hardwoods. For a given wood density, the ultimate stress in parallel-to-grain compression was higher in tropical hardwoods than in temperate hardwoods. However, the compliance coefficients for both types of woods were quite similar. Sequential extraction with organic solvents was the most suitable method for evaluating the effect of extractives on compressive properties of tropical hardwoods. The CYC and ACE fractions did not contribute to variation in these mechanical properties. The substances dissolved in MET affected positively the compliance coefficient s11 in parallel-to-grain compression and negatively the compliance coefficient s33 in tangential compression. The IG decreased the compliance coefficient s11 but also decreased the ultimate stress in parallel-to-grain compression. Finally, variations in compressive properties that were due to changes in equilibrium moisture content (EMC) were clearly influenced by wood density; denser woods were more sensitive to changes in EMC than lighter woods.

Using Acoustic Sensors to Improve the Efficiency of the Forest Value Chain in Canada: A Case Study with Laminated Veneer Lumber

Engineered wood products for structural use must meet minimum strength and stiffness criteria. This represents a major challenge for the industry as the mechanical properties of the wood resource are inherently variable. We report on a case study that was conducted in a laminated veneer lumber (LVL) mill in order to test the potential of an acoustic sensor to predict structural properties of the wood resource prior to processing. A population of 266 recently harvested aspen logs were segregated into three sub-populations based on measurements of longitudinal acoustic speed in wood using a hand tool equipped with a resonance-based acoustic sensor. Each of the three sub-populations were peeled into veneer sheets and graded for stiffness with an ultrasonic device. The average ultrasonic propagation time (UPT) of each subpopulation was 418, 440 and 453 microseconds for the green, blue, and red populations, respectively. This resulted in contrasting proportions of structural veneer grades, indicating that the efficiency of the forest value chain could be improved using acoustic sensors. A linear regression analysis also showed that the dynamic modulus of elasticity (MOE) of LVL was strongly related to static MOE (R2 = 0.83), which suggests that acoustic tools may be used for quality control during the production process.

Anatomical evaluation of wood surfaces produced by oblique cutting and face milling

The condition of superficial tissues plays an important role in the behavior of adhesive/wood interfaces. Tissues at the wood surface should be the least distorted possible during surfacing in order to avoid the formation of mechanical weak boundary layers. These layers cause significant loss of adhesion of coating films and gluelines during utilization of wood. In this study, sugar maple (Acer saccharum Marsh.), northern red oak (Quercus rubra L.), and eastern white pine (Pinus strobus L.) were surfaced by oblique cutting and face milling, while paper birch (Betula papyrifera Marsh.) was face milled. Cell damage was considerably higher in face milling than in oblique cutting. This damage was manifested in the form of lateral distortion, bending, and rupture of tissues. In general, superficial cell damage presented similar patterns for all species studied, but its severity was quite variable as a function of species and cutting conditions. The present study describes damage patterns and discusses the possible implication of cell damage in wood finishing and gluing.

Characteristics of sugar maple wood surfaces machined with the fixed-oblique knife pressure-bar cutting system

Oblique cutting differs from orthogonal cutting by an inclination given to the knife edge, which induces several changes on tool geometry, cutting forces, as well as on the quality of machined surfaces. In this work, a pressure bar was used during oblique cutting to reduce the occurrence of torn grain. The effects of cutting depth, rake angle, and oblique angle on cutting forces and surface quality were studied. Surface topography, cell damage and wetting properties were used to assess surface quality. All force components were increased by increasing cutting depth and decreasing rake and oblique angles. The lateral force, however, increased as the oblique angle increased. The surface roughness increased with increasing the lateral cutting force. Higher cutting depths and oblique angles tended to provide higher surface roughness, while higher rake angles tended to reduce surface roughness. The pressure bar was not always able to completely prevent the occurrence of defects when cutting against the grain. The occurrence of machining defects increased at higher cutting depths and oblique angles. As the rake angle decreased, the type of machining defect tended to change from torn grain to slight fuzzy grain. Moreover, the best wetting properties were obtained at lower rake angles, as they induced higher surface roughness. A 25° rake angle, a 30° oblique angle, and thinner cutting depths should be preferred to reduce dependence on ulterior sanding.