Wood and Fiber Science (E-Journal)
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EFFECT OF CHIPPING EDGE INCLINATION ANGLE ON SIZE DISTRIBUTION OF PULP CHIPS PRODUCED BY A CHIPPER-CANTER
Full text linkThe effect of oblique cutting on the chipper-canter wood chipping mechanism was studied. A bent knife was modified to obtain inclination angles (IA) of 30° and 50° between the chipping edge and the log feeding direction. The standard knife had an IA of 40°. These three knives were tested on 15 logs each, under frozen (-10°C) and unfrozen conditions. Chip dimensions were assessed by thickness (Domtar distribution) and width/length (Williams distribution). Characteristics and physical properties of the log knots were also measured. Experiments revealed that IA had a significant effect on chip formation mechanism. The IA affected the chipping edge entering the log and the form of the wood slice that was transforming into chips. These changes provoked variations in chip size. An IA of 30° produced wider chips, mostly in the first half of the cut, shaped as an elongated parallelepiped that resulted from a tangential, oblique and radial splitting in a single chip. The shape of chips obtained with IAs of 40° and 50° was more like an upright parallelepiped that was detached mostly by radial and oblique splitting. At the beginning and at the end of the cut, chips were produced by tangential splitting. As a result, for a same chip length of 23 mm, weighted mean chip thickness (WCT) decreased almost 1 mm when IA decreased from 50° to 30°. The knot ratio (total knot area / cant total area) affected both chip size distributions and WCT. Chipping frozen wood at -10°C reduced the chip thickness by 0.55 mm with respect to unfrozen wood. The amount of fines and pin chips also increased nearly two times compared to unfrozen wood. The amount of the Williams accepts chip class increased by 6% when IA decreased from 50° to 30° and by 8% when chipping unfrozen wood compared to frozen wood
WOOD PROPERTY MAPS SHOWING WOOD VARIABILITY IN MATURE LONGLEAF PINE: DOES GETTING OLD CHANGE JUVENILE TENDENCIES?
Full text linkEstablished illustrations of juvenile wood in pines depict a central core of wood, varying little by diameter or cambial age, to be nested within mature wood tapering to the upper portion of the stem; alternative illustrations show greater complexity in attributing variability within this central core of wood to its proximity to the crown and/or the maturity of the tree when the wood was formed. The present study addresses the degree to which different representations of juvenile wood are applicable to a sampling of 70-yr-old longleaf pine (Pinus palustris Mill.) trees. Wood property maps were derived from X-ray densitometry data gathered from tree disks taken at every 61 cm along each tree bole. Unique to the wood property maps herein is that the two cardinal directions of the data (north and south) were preserved, thus providing true full-stem profiles. Compared with maps reported for younger southern pines, the central core of low-density wood extending the length of the tree boles was noticeably wider at the midheight than at the lower and higher relative heights. Another difference was that the higher ring specific gravity (SG) values, particularly at the lower heights, did not extend all the way to the wood closest to the bark. Narrower ring width and higher ring SG values above the 3Q height, normally being wood features associated with higher wood quality, can be attributed to the maturity of the study trees. Altogether, the wood property maps and data comparisons were consistent with an alternative juvenile wood illustration proposing that all the wood at the base of the tree, comprised of juvenile corewood and juvenile outerwood, as being different from the majority of the tree wood, upward from a one-quarter relative height
COLOR CHANGES OF VARIOUS WOOD SPECIES IN RESPONSE TO MOISTURE
Full text linkColor including texture and gloss is one of the most important esthetical attributes of wood. For any porous materials in contact with water, the phenomenon of surface darkening arises from a change in the refractive index, as water enters air-filled pores. For the first time, this research investigated to what extent MC differences affect the surface color, below fiber saturation and after the pores are filled with water, with respect to extractive contents. Samples from 13 wood species were exposed to various climates, and as soon as EMC was reached, the color was determined. Color changes were also recorded after water submersion and also after vacuum impregnation in water. Chromaticity parameters a* and b* widely increased, along with higher moisture contents. Lightness changesweremostly stable at lower moisture contents.An exceptionwas demonstrated by the heartwood species black locust, plum, walnut, and oak, which showed a brightening effect at lowermoisture contents, followed by the darkening phase. The overall darkening of wood at high RH is connected to capillary condensation. Liquid water present in the cell lumen most caused darkening and an intensification of hue (increase in a* and b*). Darkening was even more expressed after vacuum impregnation with water. In conclusion, with only limited fluctuations in moisture contents below fiber saturation, the expected color changes are minor to neglectab
RBF based sliding mode control method for lumber drying system
Full text linkLumber is an indispensable raw material for people’s daily life. Drying process is a crucial stage in lumber manufacture. As to ensure a suitable and usable end product of lumber, most of its MC must be removed by drying. Improving the quality of lumber drying requires efficient control scheme. This article presents a design of radical basis function (RBF) neural network–based sliding mode controller for lumber drying system. RBF neural network is introduced to optimize the conventional slidingmode controller. The proposed strategy has been theoretically and experimentally investigated to demonstrate the applicability for lumber drying process. Comparative study of conventional sliding mode control (SMC) scheme and proposed control scheme is also presented. It was found that the control performance of RBF-based sliding mode controller was superior to the conventional slidingmode controller in computer simulation. Furthermore, in the field conditions, time and energy consumption reduction were noticed with RBF-based sliding mode controller compared with conventional SMC strategy using the same drying schedule, although the drying quality using the two control methods were similar
Effect of wood density and cracks on the moisture content of coated Norway spruce (Picea abies (L.) Karst)
Full text linkA protective coating is often used on the cladding of wooden facades to limit the absorption of moisture. Low wood moisture content (MC) is essential to obtain satisfactory durability performance. Wood density is known to influence the water sorption and crack formation of uncoated wood. However, the effect of density on the aforementioned behaviors of coated spruce is not yet fully understood. Six-years of data on the crack formation and the MC variation of outdoor exposed panels are analyzed in this article. The outdoor test was complemented by a subsequent laboratory experiment, wherein the MC variation was monitored at different depths on the board during artificial water spraying. The aim of this research was to increase the knowledge about how wood density and aging affect the water sorption of coated spruce through the crack formation. The results indicated that wood density had an impact on the overall sorption behavior of coated spruce. Low-density spruce contributed to faster water absorption and desorption processes than coated samples with higher density. However, the observed correlation to density was limited to a condition with an intact coating. High-density characteristics contributed to more crack formation, and the density–sorption relationship reversed with a cracked coating. A cracked coating caused a strong local increase in the MC of the wood at the location of the cracks. Weather-exposed replicates without cracks had a higher MC in the core of the board compared with the value beneath the coating. The higher MC is probably due to the water sorption of the uncoated backside of the panel. Such an occurrence raised awareness for future studies to account for multidimensional sorption behavior from all sides of the panel. The local difference in MC also raises awareness for future studies to investigate local MC variations (as opposed to the global average of the panel) in research on the durability of coated wood
DISTRIBUTIONS OF MODULUS OF ELASTICITY AND MODULUS OF RUPTURE IN FOUR MILL RUN LUMBER POPULATIONS
Full text linkThe modulus of elasticity (MOE) and modulus of rupture (MOR) of graded lumber populations are commonly modeled by normal, lognormal, or Weibull distributions, but recent research has cast doubt on the appropriateness of these models. Such modeling has implications for ultimate performance and efficiency of resource use. It has been shown mathematically that the distribution of MOR in a graded subpopulation does not have the same theoretical form as the full, ungraded (or “mill-run”) population from which it was drawn; rather, its form is pseudo-truncated, exhibiting thinned tails. Although the phenomenon of pseudo-truncation in graded populations has been well substantiated, the form of the underlying full distribution—an essential factor in characterizing the distribution of the graded population—remains unsettled. The objective of this study was to characterize the distributions of both MOE and MOR in four diverse mill-run lumber populations to determine if and to what extent the distributions of strength and stiffness in mill-run lumber are similar from mill to mill. The authors collected a mill-run sample of 200 southern pine 24 specimens from each of four sawmills, for a total of 800 test pieces. After measuring MOE and MOR, they fit candidate distributions to those data by mill and evaluated each distribution for goodness of fit. Results suggest that perhaps none of the traditional distributions of normal, lognormal, or Weibull is adequate to model MOE or MOR across all four mills; rather, MOE and MOR in full lumber populations might be better modeled by skew normal or mixed normal distributions
A REVIEW OF WOOD-BARK ADHESION: METHODS AND MECHANICS OF DEBARKING FOR WOODY BIOMASS
Full text linkDebarking systems and strategies are used to increase the value of woody biomass by separating wood and bark into two value-added product streams. Several debarking methods have been used for the removal of bark from wood. The selection of a debarking method is often based on the wood type and its end use. Debarking methods discussed briefly in this review include drum debarking, ring debarking, cradle debarking, chain flail debarking, high-pressure water jet debarking, compression debarking, and biodebarking. The performance of these debarking methods is highly dependent on operational parameters of machines, properties and type of woody biomass, and pretreatments. A universal applicable mechanistic model of the debarking process would be especially valuable for the development and optimization of debarking systems. In this respect, the competing objectives of high bark removal, low wood damage, high throughput, and low energy must be balanced against one another to arrive at a truly optimized approach. Wood-bark bond strength plays a vital role in impacting the effectiveness and efficiency of debarking technology. Thus, it is important to understand how mechanical properties of the wood-bark interface are influenced by different factors. Key factors that affect the wood-bark bond strength include MC, harvest season, wood species, temperature, and direction of applied load. The likely reason why MC affects the wood-bark adhesion strength is that the constituent elements of primary plant cell walls (cellulose, hemicellulose, and pectin) behave differently when they are exposed to water molecules. For example, there is negligible change in the length if cellulose microfibrils when exposed to water molecules. However, characteristics of hemicellulose and pectin behave differently than cellulose when they contact with water molecules. Also, the difference in the adhesion strength of wood-bark bond among varieties of woody plants is possibly due to the difference in density of cross linkages of homogalacturonan pectin by Ca2., and arabinan and galactan side chains of pectin. The relevance of this information to the debarking process is discussed
TECHNICAL NOTE: Effects of Polyurethane Resin on the Physical and Mechanical Properties of Wood Fiber/Palm Kernel Shell Composite Boards
Full text linkThis article investigates the effect of polyurethan (PU) resin as a binding agend for wood fiber (WF)_ and palm kernel shell (PKS) composite boardl in terms of physical and mechanical properties. A series of fiberboard samples consisting of WF/PKS at a ratio of 85/15 with different percentage of PU adhesive (40%, 50% and 60%) have been fabricated. The results showed that flexural modulus, flexural strength, tensile modulus, tensile strength and hardness of the boards were increased with the increase of PU adhesive percentage. The effects of the binder were also explained in terms of porosity and surface morphology. Based on the results, the board met the Japanese Industrial Standard A 5905 for type 5 and can be classified as medium density fibreboard, which could potentially be used in the decoration application. Replacing formaldehyde with the PU resin as a binding agent in fiberboard composites is one way to avoiding health issues.
WITHIN-MILL VARIATION IN THE MEANS AND VARIANCES OF MOE AND MOR OF MILL-RUN LUMBER OVER TIME
Full text linkThe literature related to the phenomenon of pseudo-truncation has emphasized that the mechanical property distributions of graded lumber subpopulations are determined by the mechanical property distributions of the mill-run (or full) lumber populations from which the subpopulations are formed. Whereas previous studies have shown that the means and variances of mechanical properties in the same visual grade of lumber can vary from mill to mill, there have been no studies on the stability of the means and variances of MOE and modulus of rupture (MOR) in mill-run lumber populations at the same mill over time. The objective of this study was to investigate if statistically significant differences between the means and variances of MOE and MOR in mill-run lumber populations at the same mill could be observed across samples taken several months apart. Two mill-run samples of 200 pieces of rough, dry 2x4 southern pine lumber were taken from each of four Mississippi sawmills: one in the summer and one in the winter. For each mill, the summer and winter means and variances of flexural MOR and MOE were compared. Whereas no significant differences were found between the mean MOE and/or mean MOR of the summer and winter samples from Mills 2 and 4, significant differences in mean MOE and/or MOR were found between the summer and winter samples from Mills 1 and 3. In addition, a Levene’s test on the MOR of Mill 1 showed significant differences in the variance between the summer and winter samples. Further analysis revealed that in addition to the fact that the winter mill-run sample from Mill 3 was made up of a larger percentage of lower grade material than the summer sample, there were pronounced strength differences between the summer and winter samples both around the median and at the lowest (near-minimum) percentiles within each grade. This reinforces the notion that changes in mill-run MOR distributions over time can have an important effect on the overall strength of a given mill’s visual grades over time. A theory of mixed distributions could account for these differences.