Moisture Sorption Properties of Hardwoods as Affected by their Extraneous Substances, Wood Density, and Interlocked Grain

Wood samples of nine tropical hardwoods from Peru and sugar maple from Quebec were selected for moisture sorption tests using a multiple step procedure at 25°C. Cold-water and hot-water extractives, sequential cyclohexane, acetone, and methanol extracts, ash content, wood density, and interlocked grain also were evaluated on matched samples. Wood extractives, interlocked grain, equilibrium moisture content (EMC), and hygroscopic stability were highly variable within and among wood species. Sequential extraction with organic solvents was the most suitable method for evaluating the effect of extractives on sorption behavior in tropical hardwoods. Cyclohexane extractives had a little influence on EMC. The acetone fraction was the most significant variable affecting EMC and hygroscopic stability of tropical hardwoods, while the methanol fraction had a negligible effect on the sorption behavior of these species. In general, EMC decreased and hygroscopic stability increased as the concentration of acetone extractives increased. The influence of these acetone-soluble compounds on EMC decreased as relative humidity increased. However, the acetone fraction of copaiba (Copaifera sp.), and probably caoba (Swietenia sp.), appeared to play a hydrophilic role in controlling the EMC of wood. Finally, EMC also decreased as wood density and interlocked grain increased

Influence of Moisture Sorption on the Compressive Properties of Hardwoods

Samples of nine tropical hardwoods from Peru and sugar maple wood from Quebec were selected to undergo moisture sorption tests associated with either a parallel to grain compression test or a perpendicular to grain tangential compression test at 25 C. Results indicated that, for a given equilibrium moisture content, the transverse strength is lower after desorption than after adsorption. The magnitude of this phenomenon, called second-order effects of moisture sorption, varied with the species and with the mode of measurement of the strain. Hence, it seems that the distribution of deformation influences the second-order effects in tangential compression. Also, it was shown that second-order effects of moisture sorption associated with parallel to grain compression strength are explained by those related to the transverse swelling of wood. These effects are thereby proportionally greater in the perpendicular to grain direction of wood than in the parallel to grain direction

Swelling Properties of Hardwoods as Affected by their Extraneous Substances, Wood Density, and Interlocked Grain

Samples of nine tropical hardwoods from Peru and sugar maple wood from Quebec were selected to perform moisture sorption tests associated with swelling tests using a multiple step procedure at 25°C. Cold-water and hot-water extractives, sequential cyclohexane, acetone, and methanol extracts, ash content, wood density, and interlocked grain also were evaluated on matched samples. Swelling properties were highly variable within and among wood species. The wood density corrected for the extraneous substances was the most significant variable positively affecting the transverse and volumetric swelling of tropical hardwoods. Sequential extraction with organic solvents was the most suitable method for evaluating the effect of extractives on swelling properties of tropical hardwoods. The extractives soluble in cyclohexane were the more accessible, but they virtually did not contribute to wood swelling. The substances dissolved in acetone appeared to be located within cell walls. After wood density, these compounds were the most significant variable negatively affecting the radial swelling. The substances dissolved in methanol were located within cell walls. After wood density, this extracted fraction was the most significant variable negatively affecting the tangential swelling. The acetone and methanol extracted fractions positively affected the dimensional stability of tropical hardwoods. Finally, the effect of the interlocked grain on swelling was only indirect given that this grain pattern reduces the equilibrium moisture content

Effect of Re-Wetting Treatment on the Dimensional Changes of Sugar Maple Wood

Air-dry wood samples are often simply re-wetted by direct immersion in order to raise the moisture content above the fiber saturation point. It is assumed that this treatment has no effect on the properties of wood and is equivalent to the green condition. A preliminary study was undertaken here to evaluate the influence of water re-saturation processes on the dimensional changes in sugar maple wood. Matched samples were subjected to three different full-water saturation treatments, from a four-step mild procedure to a one-step drastic procedure. Results showed that the re-wetting process had a significant effect on swelling and shrinkage of sugar maple wood

The Influence of Cutting Parameters on the Surface Quality of Routed Paper Birch and Surface Roughness Prediction Modeling

The objective of this study was to characterize the routing process to better understand the machining conditions that affect surface finish. Experiments were designed to determine the impact of cutting depth, feed speed, and grain orientation of the workpiece on the surface quality of paper birch wood. Statistical analysis showed that the cutting depth did not influence surface finish. Roughness depended greatly on feed speed and grain orientation, increasing linearly as the feed speed increased. The roughest surfaces were obtained by routing against the grain between 120 and 135° grain orientation, depending on the feed speed. Two models able to predict the surface finish based on initial cutting parameters were developed and compared. Both the statistical regression and neural network models were subjected to a validation procedure in which their performance was confirmed using data that were not used for the learning process. Results indicated that the neural network system estimates the surface roughness with less error than the statistical regression model

Changes in Physical Properties of Yellow Birch Below and Above the Fiber Saturation Point

Two experimental techniques were used to perform moisture sorption tests at 25°C on specimens of yellow birch sapwood. The first used saturated salt solutions (from 33% to 90% relative humidity), and the second used the pressure membrane method (above 96% relative humidity). These sorption tests were combined with dimensional measurements and perpendicular-to-the-grain tangential compression tests. Results showed that at equilibrium moisture content, radial, tangential, and volumetric shrinkage, as well as changes in transverse strength, occur above the fiber saturation point. 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 water, which contradicts the concept of FSP. The initial equilibrium moisture content at which bound water is removed from yellow birch was about 41%

Analysis of Cutting Forces in Straight-Knife Peripheral Cutting of Wood

Effects of rake angle, wavelength, and depth of cut on cutting forces during straight-knife peripheral milling of sugar maple were determined. Progressions of normal (FN) and parallel (FP) force components during a typical up-milling cycle were determined. Results showed that at the initial step of the cut, FN was negative, ie the knife edge pushed the workpiece downward. The part of the knife path that remained visible on the machined surface was always created in such a situation. As the knife edge advanced in the cutting path, FN increased, reached a maximum negative value, then decreased to 0 N/mm, turned positive, and continued upward. FP was always positive and increased as chip thickness increased. Positive FN and FP reached a maximum just prior to emergence of the knife from the workpiece at about the maximum thickness position. However, when chip splitting occurred, the maximum positive FN and FP occurred before that maximum thickness position was reached. Maximum negative FN and FP increased as rake angle decreased and as wavelength increased. Maximum positive FN increased as rake angle and wavelength increased. Maximum positive FN and FP were also affected by depth of cut but to a lesser degree. Impact of these maximum cutting forces on production of defects was analyzed, and ways to decrease them were discussed

Performance of Three Alternative Surfacing Processes on Black Spruce Wood and Their Effects on Water-Based Coating Adhesion

Surface quality and water-based coating performance of samples prepared by oblique cutting, helical planing, and face milling were studied. Oblique cutting and helical planing generated surfaces with similar features. Samples had little subsurface damage and fibrillation, and few cell lumens were accessible on the surface to favor coating penetration. As a result, these samples had lower surface roughness and wetting properties than face-milled ones. Face-milled samples were defined by more subsurface damage, fibrillation, and open lumens that favored coating penetration. However, the pull-off strength of face-milled samples was significantly lower after accelerated weathering than the oblique-cut or helical-planed samples. Hence, oblique cutting and helical planing are suitable for preparing surfaces of black spruce prior to coating application. No correlations were detected between surface quality parameters and adhesion, which indicates that pull-off tests have to be determined to quantify coating adhesion on surfaces of this wood species

Effect of Knife Jointing on the Gluing Properties of Wood

Jointing is a common practice required to produce the same cutting circle for all knives mounted in a culterhead of a peripheral knife planer. This practice also is sometimes used wrongly to refresh slightly dulled knives. Initially the jointed land at the cutting edge has a 0 degree clearance angle, which becomes negative with the workpiece motion relative to the cutterhead and as the cutting edge wears. The jointing operation potentially could crush a thin layer of the planed board and affect the wood quality and performance. The gluing properties of sugar maple, red oak, and spruce woods were evaluated using four jointed land widths. A wider jointed land affected the surface quality and resulting gluing shear strength differently depending on anatomical differences of the specific woods. The effect of knife jointing was more pronounced where the moisture content of the samples had fluctuated

Evaluation of Four Surfacing Methods on Black Spruce Wood in Relation to Poly(Vinyl Acetate) Gluing Performance

Oblique cutting, peripheral planing, face milling, and sanding were used to surface black spruce wood prior to gluing with a two-component poly(vinyl acetate) adhesive. Surface roughness, anatomical features of surfaces, and glueline interfaces as well as the glueline shear strength before and after aging were evaluated. Oblique-cut surfaces presented no subsurface damage, little fibrillation, low roughness, thin gluelines, and little adhesive penetration. Peripheral-planed and face-milled surfaces both showed slight cell deformation and a higher level of fibrillation. The large number of cell lumens available and the fibrillation appeared to favor the penetration of adhesive as well as to increase surface roughness. Sanded surfaces were the smoothest, and their anatomical structures were the least visible of the four machining processes. These samples also showed more important subsurface damage, which limited the penetration of adhesive. For the glueline shear strength before and after weathering, no significant differences occurred among the surfacing treatments. The microscopic and topographic differences among the surfacing treatments were not sufficient to generate significant differences in glueline shear strength. Peripheral planing and face milling should be better alternatives with respect to productivity