Showing papers in "Wood and Fiber Science in 1974"

Hydrogen Peroxide and Iron: A Proposed System for Decomposition of Wood by Brown-rot Basidiomycetes

Abstract: Low concentrations of H 2 O 2 and Fe ++ caused rapid weight loss of wood of sweetgum and loblolly pine. The degree of polymerization of cellulose in treated woods decreased rapidly at low weight loss and then diminished gradually. The alkali solubility of exposed woods increased rapidly at low weight loss and was inversely related to the degree of polymerization. The H 2 O 2 -Fe system solubilized hemicelluloses of both woods more readily than cellulose. Lignin of sweetgum, but not pine, was changed so that it was solubilized by strong acid hydrolysis. The optimal pH for weight loss was about 3.3 for sweetgum and 3.0 for pine. Wood of both species absorbed much of the available Fe from solution. The literature suggests that brown-rot is oxidative rather than being strictly hydrolytic. The H 2 O 2 -Fe ++ system oxidizes cotton cellulose, and it essentially reproduced in wood and wood cellulose, characteristics of brown-rot basidiomycetes. These fungi produce H 2 O 2 from native substrates in wood (Koenigs, 1974) and the optimal pH for degradation. Thus, it is proposed that these fungi may attack cellulose and partly decay wood via an H 2 O 2 -Fe ++ system.

Effect of Size on Tension Perpendicular-To-Grain Strength of Douglas-Fir

Abstract: The strength of wood in tension perpendicular-to-grain has been studied by several authors and found to depend on specimen geometry In this paper, the weakest-link concept has been applied to predict the relationship between specimen volume and load-carrying capacity for Douglas-fir specimens loaded in uniform tension perpendicular-to-grain The theory allowed the prediction that logarithm of maximum strength should decrease linearly with logarithm of volume Experimental data taken from the literature were used to evaluate the theoretical model and agreement was found to be high (R 2 ≥ 085) Average strength of a unit volume is approximately 460 psi, whereas the predicted strength of a 10- X 10- X 20-inch specimen (2000 inches 3 ) is approximately 100 psi The magnitude of the size effect may depend on the quality of material in the specimens, but certainly any rational development of working stresses for tension perpendicular-to-grain must consider effects of specimen (or structural component) size

Relative Permeability and the Gross Pore Structure of Wood

Abstract: Water-saturated, longitudinal core samples of nine hardwoods and three softwoods were measured for specific permeability and also for relative permeability to water and nitrogen gas. Constant flow rates were achieved for specific permeability. Relative permeability curve shapes were influenced more by the pore structure of wood than by its specific permeability. It appears that softwoods could be drained much lower in degree of saturation than hardwoods. In imbibition-type measurements, the softwoods were higher in saturation but lower in relative permeability than the hardwoods.

Some Physical Properties of Birch Carbonized in A Nitrogen Atmosphere

Abstract: The dynamic mechanical properties, mass loss, and shrinkage data of birch carbonized in a nitrogen atmosphere to different temperatures from 473 to 973 K have been investigated. The dynamic elastic modulus data decreased as the heat treatment temperatures approached 673 K. Major mass loss and shrinkage accompanied the decrease in the modulus data. Treatments at higher temperatures (> 673 K) produced substantially less additional mass loss and shrinkage but produced increased rigidity in the char. The internal friction behavior of the char was complex.

permeability of twenty-two small diameter hardwoods growing on southern pine sites

Abstract: Gas permeability of hardwoods growing on southern pine sites is significantly affected by moisture content in the longitudinal direction The ratio of permeability in the transverse to longitudinal directions is from 12,000:1 for post oak to over 1,000,000:1 for other oaks, but it is not affected by moisture Although variation in longitudinal permeability varies greatly between and among species, for most species there was no height effect A significant difference was detected between sapwood and corewood only in the longitudinal direction Gas permeability tended to be somewhat less than liquid permeability

The Effects of Dwarf Mistletoe on The Wood Properties of Lodgepole Pine

Abstract: The effects of dwarf mistletoe ( Arceuthobium americanum Nutt. ex. Engelm.) on the wood properties of lodgepole pine ( Pinus contorta Dougl.) were studied. The results indicate: a decline in modulus of elasticity, modulus of rupture, and work to proportional limit in both infected and noninfected wood from the infected trees; a higher specific gravity of the infected wood; a higher percentage of alcohol-benzene extractives in the infected wood; an increase in longitudinal shrinkage in both infected and noninfected wood from the same tree; a lower percentage of latewood in wood from infected trees; no significant difference in growth ring width between infected and control wood; narrower growth rings in the noninfected regions of infected trees; a decrease in tracheid length in both infected and noninfected wood from the same tree; an increase in microfibril angle in both infected and noninfected wood from the same tree. This is the first study to show that both infected wood and noninfected wood from the same tree are definitely inferior to wood from noninfected trees in strength and longitudinal shrinkage characteristics.

Relationship of Climate to the Specific Gravity of Four Costa Rican Hardwoods: An Exploratory Study

Abstract: In the summer of 1970, increment cores were removed at breast height from trees of four hardwood species growing on ten different sites in Costa Rica. On the basis of Holridge's Life Zone Classification System, these sites ranged from Tropical Dry to Premontane Rain. Expressed in terms of Holdridge's Life Zone System, climate has the most pronounced effect on the specific gravity of Cordia alliodora; —specific gravities for Tropical Dry and Premontane Moist sites being significantly greater than those for Tropical Moist, Premontane Wet and Tropical Wet sites. The specific gravities of Virola Koschnyi and Cedrela mexicana are also significantly different on some sites. For Brosimum spp., no significant differences in specific gravity were found.

The Role of Extractives in the Hydrophobic Behavior of Loblolly Pine Rhytidome

Abstract: Wettability, as indicated by contact angle with water, of phellogen and old phloem surfaces of loblolly pine ( Pinus taeda ) rhytidome was determined after extraction, heating, and aging. These two tissues are the predominant surfaces exposed after milling pine bark into small particles. Contact angles measured for bark surfaces were over 50% higher than those published for wood. Old phloem gave an average angle of 118° while phellogen was significantly more wettable with an average contact angle of 106°. Extraction of bark by diethyl ether and methanol increased wettability. Furthermore, large contact angles were measured on glass plates covered with condensed bark extractives. Heat treatments at 105 C for 78 hr increased the contact angle, thus decreasing wettability. The influence of heating time on contact angle was described by an exponential function whose coefficients were used for quantitative assessment of the treatment effects. Surface aging was shown to involve the same general physico-chemical processes as heating. Effects of heating were shown to be related to ether and methanol soluble extractives in loblolly pine bark.

A Technique for Determining The Transverse Dimensions of the Fibres in Wood

Abstract: For softwoods, fibre width can be calculated from a count by optical microscopy of the number of cells per unit area (N) in the cross-sectional face of a small block of wood. Assuming a square cross section for the average fibre, the fibre width (b) is given by b = (1/N) 1/2 . Lumen width (a) can be calculated from the fibre width thus obtained and a measurement of the bulk density of the wood (D B ) using the theoretically derived relationship a/b = (1 - D B /D C ) 1/2 . D C is the cell-wall density, which to a good approximation is a constant from one wood to another. For hardwoods, the count of cells per unit area is restricted to areas occupied by the libriform fibres, and the bulk density used is that of the part of the wood occupied by these fibres. This bulk density may be calculated from the bulk density of the whole wood using a measurement of the fraction of the total volume occupied by vessels and ray cells. The results so obtained are in close agreement with those obtained by direct measurement using scanning electron microscopy and are believed to be superior to those previously obtained by the usual expedient of direct measurement by optical microscopy. This is particularly true of cell-wall thickness, (b-a)/2, the direct measurement of which has recently been shown to be subject to many sources of error. A simple experimental procedure for measuring the dry-bulk density of small samples of wood is described and the work is illustrated by measurements of the fibre width, cell-wall thickness, and fibre coarseness of some thirty species of wood.

Measuring Dependence of Diffusion Coefficient of Wood on Moisture Concentration by Adsorption Experiments

Abstract: The dependence of the diffusion coefficient on moisture concentration of aspen wood at 110 F was determined by using an experimental method that requires a series of adsorption experiments and by applying a numerical method that includes using a finite difference technique to solve the diffusion equation with a diffusion coefficient that is dependent on concentration. The analysis showed that the diffusion coefficient increases with mosture content. Between 2.5 and 18.0% moisture content, the diffusion coefficient increases by a factor of 8.

The Birefringence of Wood Pulp Fibres and The Thickness of the S 1 and S 3 Layers

Abstract: The birefringence of pulped softwood fibres has been measured and found for several species to decrease with decreasing cell-wall thickness. This is explained theoretically by the compensation of the retardation of light in the S 2 layer by the transversely wound S 1 and S 3 layers. These layers are of similar thickness for all fibres and thus have a greater effect on thin-walled fibres. Measurement of birefringence over a range of fibre wall thicknesses permits a determination of the thickness of the S 1 and S 3 layers, and the results are in good agreement with data from other methods.

The Interdependence of the Lignin Content and Electrical Properties of Wood

Abstract: A linear relationship was found to exist between the percentage of acid-insoluble lignin content and both the permittivity and DC conductivity of vacuum-dried woods, woods conditioned at 65% relative humidity, and in both of the two major grain directions. This study shows that dielectric measurements could be developed into a nondestructive analytical tool for estimating acid-insoluble lignin content in woods.

Chemical and Physical Properties of Tumor-Affected Sitka Spruce

Abstract: The chemical composition, fiber properties, and pulpability of a Sitka spruce ( Picea sitchensis ) massive trunk and root tumor were compared with normal second-growth wood. In general appearance the tumored tissue looked like normal wood in that it had annual rings and definite sapwood and heartwood zones. However, the trunk tumor showed no visible evidence of compression wood, whereas the trunk of the affected tree above and below the tumor contained about 30% compression wood. The tumor tracheids were short, curved, and twisted; and numerous traumatic resin canals were present. The wood rays and bark showed no apparent abnormalities. Paper prepared from kraft pulp tumor wood was lower in burst, tear, tensile, and opacity, and higher in fold and shrinkage, density and air resistance compared to pulp from the second-growth control. Chemical analysis indicated that the tumor-affected tree had a higher hemicellulose content, primarily as galactan-containing polymers, than the second-growth control. The factor causing the tumor growth was not ascertained in this study.

Penetration of Water into Hardwoods

Abstract: The longitudinal penetration of water into hardwoods was studied by continuously measuring swelling and uptake in a swelling cell apparatus. Mathematical equations were developed to relate swelling, bound moisture uptake, free moisture uptake, and time of penetration. The initial stages of bound moisture uptake and free moisture uptake were each shown to be linear when plotted against the square root of time. Bound and free moisture penetration constants were calculated from swelling and uptake data for different wood species at different temperatures. The transport of bound water by vapor and water diffusion became more important than transport by capillarity as temperature increased, or when wood species with obstructed vessels were used. The relative amount of water uptake distributed between bound moisture and free moisture was shown to change with increasing temperature.

Longitudinal Diffusion and Permeability of Nonpolar Gases in Eastern Hemlock

Abstract: Longitudinal ethane diffusion and nitrogen permeability were measured in oven-dry eastern hemlock sapwood. Samples were selected from 2 trees, 3 heights, and 4 quadrants, and either air- or solvent-dried for aspirated or unaspirated conditions. An IR method was used to detect ethane concentration in nitrogen at 25 C from which diffusion coefficients were calculated. The mean diffusion coefficient of the solvent-dried samples was 40% of free diffusion; the air-dried coefficient was about 16% of the free diffusion coefficient. No significant differences were found between position in the tree or oven-dry density and the diffusion coefficients. Diffusion coefficients were used to determine tortuosity differences in air- and solvent-dried wood. Effective pore openings obtained from permeability measurements, the Klinkenberg equation, and the temperature coefficient of diffusion confirmed that diffusion was occurring in the Kundsen end of the slip-flow region. A linear relationship was found between the permeability constant and diffusion coefficient. Diffusion and permeability measurements produce separate and complementary data that can be used to determine the mode of conductivity of gases in wood.

A Note on the Protection of Wooden Beams Exposed to an Acidic, Humid Atmosphere

Abstract: By means of standard lignin and carbohydrate analyses, together with pH measurements, the cause of strength losses in beams exposed to an acidic, humid atmosphere was shown to be due to acid hydrolysis of wood carbohydrates. It is recommended that wooden beams used in such an acidic environment be adequately finished with a flexible, moisture-proof coating and the finish be inspected and maintained at regular intervals.

Comparison of Exclusion Values for Lumber Strength

Abstract: There exists a temptation to utilize the distribution-free methods of ASTM D2915-70T for the comparison of the strengths of lumber populations, a use outside the intent of the standard. It is shown that the precision of such procedure is highly dependent on the form of the parent distribution of strength. Since this form is in general unknown, the confidence to be ascribed to inferences concerning near-minimum values of two lumber populations is also unknown and may well be inadequate.