Wood and Fiber Science (E-Journal)
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Mechanism of Voc Release From High-Temperature Southern Pine Lumber Drying
Get PDFHydrocarbon (Method 25A) emissions from drying southern pine lumber have been measured in full-scale experiments. The mechanism proposed comprises three components: release of turpentine dissolved in the surface layer of water on the wood, water-mediated transport of turpentine from the interior of the wood to the surface, and evaporation of turpentine during the falling rate period. The result allows the total Method 25A release to be estimated without knowledge of the airflow through the kiln. Full-scale Method 25A emissions from lumber can be predicted from laboratory work on sawdust, indicating that the mechanism is independent of the type of furnish
In-Plane Dimensional Stability of Oriented Strand Panel: Effect of Processing Variables
Get PDFSingle-layer oriented strand panels were fabricated under a combination of three alignment levels, four densities, and two resin contents. Flake orientation, density gradient across panel thickness, linear expansion (LE), and bending properties were measured. Flake orientation was characterized with the von Mises distribution using mean flake angle and concentration parameter.It was shown that the shape of the LE-moisture content change curve varied with alignment level and test direction. The variation was attributed to whether the LE of a panel was controlled by transverse or longitudinal wood swelling along a particular test direction. Total LE from oven-dry to water-soak condition, modulus of elasticity (MOE), and modulus of rupture (MOR) varied significantly with flake orientation distribution and density. Effects of resin content at the levels used on LE, MOE, and MOR was relatively small and was more diversified. The LE, MOE, and MOR were correlated with the concentration parameter, density, resin content, and moisture content using a power form equation. The experimental data form a database of layer properties for modeling three-layer, cross-laminated oriented strandboards (OSBs) manufactured under hot pressing
The Influence of Small Grain Angle Variation on Toughness
Get PDFToughness of solid wood as determined by ASTM D143-52 is known to be sensitive to slope-of-grain in the specimen. Although samples with observed sloping grain are routinely rejected, localized grain deviations in the center of nominally straight-grained specimens may escape detection. The acceptance of this sample is often aided by the difficulty in identifying the grain orientation at a point and by the usual large number of toughness tests that are conducted in any one experiment. In this study 226 standard toughness specimens of redwood were carefully machined to be straight-grained. However, close scrutiny of the center of the specimens (often after they had been failed) showed that only 10 of the 226 samples had truly straight grain and that localized grain deviations ranged from zero to 15°. Regression analysis showed that the slope-of-grain on the specimen face parallel to the impact direction explained a significant amount of variation in toughness. If this slope was accounted for, the coefficients of variation of toughness were reduced from 33 and 30% to 22 and 18% for impact in the radial and tangential direction, respectively. The results of the study showed that toughness was very sensitive to small localized grain deviations and that truly straight-grained toughness samples are rare. A significant amount of the usual high variation in toughness data could be attributed to these small grain deviations
Effects of Precommercial Thinning on Annual Radial Growth and Wood Density in Balsam Fir (Abies balsamea)
Get PDFThis study examined effects of precommercial thinning (PCT) on annual radial growth (ring width) and wood density in balsam fir [Abies balsamea (L.) Mill.]. In addition, the responses to PCT were measured and compared at several stem heights (0.2 m, 0.7 m, 1.3 m, 3 m, 5 m, 7 m, 9 m). Fifty-four trees were collected from plots subjected to moderate thinning (nominal stand density of 2,150 stems/ha), and light thinning (nominal stand density of 4,200 stems/ha), and from control plots. Ring width and wood density of individual rings were measured by X-ray densitometry. Our results show that in balsam fir the annual radial growth rate showed a positive response to PCT, especially in the low part of the stem (up to 5 m high), and this response lasted for 7 years. To achieve a significant increase in annual diameter growth in this species, however, a moderate thinning intensity is needed. This study also revealed that the response of annual radial growth to PCT was limited primarily to the earlywood width, whereas the latewood width showed little response. As a result, the latewood percentage was affected by the moderate thinning. The light thinning and the control plots, however, had a comparable earlywood width and latewood percentage. Both earlywood density and latewood density showed little response to PCT. However, the wood density of growth rings tended to decrease following the moderate thinning, due to a decreased latewood percentage. In addition, the moderate thinning might somehow reduce the intra-ring variation in wood density and thus produce more uniform wood. This study also revealed that the responses to thinning in this species tended to weaken appreciably with increasing stem height. The remarkable responses were observed in the low part of the stem (up to 5 m high), whereas little response was found at the upper part of the stem. As a result, an increased stem taper may result from PCT in balsam fir
A Study of Loblolly Pine Growth Increments—Part III Refining Characteristics of Tracheids from Kraft Pulps
Get PDFGrowth increments of loblolly pine were divided into five growth zones and kraft-pulped according to four different digestion schedules of 1 1/2, 1 3/4, 2, and 3 hours. Each of the 20 pulps was subjected to four periods of beating and Canadian Standard Freeness (CSF) was determined for each. It was found that all pulps independent of the extent of digestion or origin of wood from the growth ring had about the same CSF after short periods of beating. After 35 minutes in the beater, latewood pulp freeness was drastically reduced whereas earlywood pulps changed very little. In general, significantly less energy, as indicated by shorter beating times, was needed for latewood pulps to achieve a specific CSF level than for earlywood pulp. Pulps of low yield were easier to refine than those of high yield. Scanning electron microscopic observations revealed that all pulps underwent a tracheid cell-wall peeling sequence. The layer removed from latewood tracheids by beating separated into long fibrillar bundles while earlywood lamellae freed from tracheids remained intact. The influence of this external fibrillation was attributed to differences between the pulps in refining
Characterization and Modeling of Knots in Black Spruce (Picea Mariana) Logs
Get PDFA knot study on black spruce was performed on 21 trees originating from a natural stand located in Quebec. Branch (knot) frequency, distribution, and diameter along different directions in the trees were evaluated. A destructive protocol for dissection was developed to slice each knot into a series of sections for modeling the knot morphology (or internal distribution) within the log. In addition, attempts were made to establish the relationship between external branch parameters and internal knot morphology.The study showed that there were higher numbers of knots on the southern sides of the trees than on the northern sides, but the knot diameters on average were smaller on the southern sides. This heterogeneous distribution of knots around the stem may increase the chance of finding a log rotation that is optimal for lumber grade yield when the knots are considered during breakdown.The dissection data were smoothed with second degree polynomial equations using an SAS® program. The equations yielded knot angles and other knot dimensional characteristics. The study indicated that internal knots in black spruce logs showed large variations in their angles, but their diameters could be predicted from the external measurements. This information is particularly important for sawing and grading models that require precise diameter data
Transverse Compression Strength and Fracture of Spruce Wood Modified by Melamine-Formaldehyde Impregnation of Cell Walls
Get PDFIn comparison with mechanical properties in longitudinal direction, the transverse mechanical properties of wood are far from satisfying. In an attempt to modify wood for improved transverse compression strength and stiffness, spruce wood samples were impregnated with an aqueous solution of melamine-formaldehyde resin. After polymerization, the tangential compression strength of treated samples was 82% higher compared to the untreated reference, and radial compression strength had increased by 290%. The average resin concentration in the cell walls of treated samples amounted to 0.125 g g-1, as measured with the UV-microscope. In contrast, less than 2% of the cell cavities (lumina), were found to be filled with resin. Thus the improvement of strength and stiffness obtained is attributed to modification of the cell wall and not to filing of tracheid lumina. Yielding-behavior under excessive compression load changed from plastic buckling in the reference samples to brittle fracture of cell walls in the treated samples. Even though a certain increase of brittleness has to be tolerated, it is demonstrated that melamine-formaldehyde reinforcement of cell walls has a distinctly improving effect on the properties of spruce in transverse compression
Influence of Fungal Decay and Moisture Absorption on Mechanical Properties of Extruded Wood-Plastic Composites
Get PDFIn previous research on the effects of fungal decay on the mechanical properties of wood-plastic composites (WPC), results were inconclusive due to the influence of moisture absorption. This study was conducted to clarify the contributions of moisture and wood decay fungi to WPC damage. Changes in flexural strength (MOR), modulus (MOE), and weight of two extruded wood-polyethylene composite (WPC) formulations, yellow-poplar sapwood and redwood heartwood, were compared following 3 months of incubation with wood decay fungi. All materials were evaluated using modified agar-block tests in which the white-rot fungus Trametes versicolor and the brown-rot fungus Gloeophyllum trabeum were employed as test fungi. In addition, soil-block tests were performed with yellow-poplar, one WPC formulation, and T. versicolor as test fungus only. It was determined that stiffness of WPC was affected more severely by moisture absorption than by fungal colonization. Strength of WPC was not affected by decay fungi but significantly (p = 0.0001) reduced by moisture absorption for a formulation containing 70% wood filler. Calculation of weight loss in WPC was based on the wood fraction only. Modified agar-block and soil-block tests were equally suited for determining weight loss in WPC, but agar-block tests could be completed in a shorter time span. Weight loss of a formulation with 70% wood filler and incubated with T. versicolor was twice as high as that of redwood in a modified agar-block test (6% versus 3%); however, only 1% weight loss was obtained when the formulation contained 49% wood filler. These results indicate that WPC can be designed to provide high fungal durability by controlling the material composition of the formulation. Weight loss is a more sensitive indicator of fungal decay than strength and stiffness measurements in WPC as well as in redwood
Deuterium as a Novel Tracer for Determining Moisture Sources in Building Systems
Get PDFMany current problems in moisture-related deterioration of housing are found in the building envelope. Components such as interior surfaces, siding, millwork, sheathing, and framing are damaged due to excessive moisture accumulation, which leads to potential biodeterioration (mold and decay). The monetary and health implications of such widespread failures are severely impacting the housing industry. In certain individual cases of wood wetting, the source of liquid water is readily determined: typically, a failure of external sealing allows direct ingress of precipitation into the wall system. There is, however, still a debate on the role of subsequent moisture movement or condensation (from water vapor movement to a cool surface) in wall and roofing system failures. Here we show that deuterium-labeled water introduced into wood through either liquid or vapor phase can be recovered via distillation or mechanical expression. The use of deuterium as a moisture tracer can assist in determining the origin of moisture (particularly through the vapor phase transition), provide insight into current recommended practices for moisture control in buildings, and assess the application of current moisture modeling on existing moisture failures