Morphological and Bark Strength Characteristics Important to Wood/Bark Adhesion in Hardwoods

Dormant season wood/bark adhesion was determined for twenty-four hardwood species using a previously described Instron testing machine method. Wood/bark adhesion was compared, using simple and multiple correlation techniques, with bark specific gravity, inner bark strength, bark toughness, wood specific gravity, wood toughness, percent bark fibers, and percent sclereids. Wood/bark adhesion was found to be positively correlated with percent bark fibers, bark toughness, and inner bark strength. Wood/bark adhesion was negatively correlated with percent sclereids in the bark. Morphologically, it appeared that the presence of fibers increased inner bark strength, sclereids decreased inner bark strength, and inner bark strength had a major influence on wood/bark adhesion. A multiple correlation comparison employing wood toughness and inner bark strength accounted for 69% of the wood/bark adhesion encountered

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

Genetic Variation of Wood Density in Luanta Fir Tested in Central Taiwan

Forty-nine wind-pollinated families representing 8 provenances of Luanta fir (Cunninghamia konishii) were sampled from the species' range in Taiwan. The study plantation was established in central Taiwan with 49 ten-tree linear plots in each of 5 blocks in the randomized complete block design. In July 1998 at plantation age 25, a 0.45-cm caliber increment core sample was extracted at breast height in the east cardinal direction from the best tree per plot; altogether 245 cores (1 core/family/plot X 49 families X 5 blocks) were sampled. From each core, only the 6 outermost growth rings (near the bark) were used to determine extracted specific gravity according to the maximum moisture content method. Genetic variations among provenances and among families within provenances were tested following a general linear model. There was no apparent geographic variation pattern, and the main source of specific gravity variation was attributable to differences among families within provenance. Overall specific gravity was 0.36 and the narrow-sense family heritability was 0.46. Wood specific gravity is strongly controlled by additive genetic variance, suggesting that this trait would respond to selection breeding. The importance of family selection was emphasized in the improvement of this wood property in Taiwan

Fungal Decay Resistance and Dimensional Stability of Loblolly Pine Reacted with 1,6-Diisocyanatohexane

Wood reacted with 1,6-diisocyanatohexane resisted fungal attack and had improved dimensional stability. At 25.8% chemical weight gain, the reacted wood had no weight loss by the brown-rot fungus Gloeophyllum trabeum; at 20.9% and 23.8% chemical weight gains, the reacted wood had antishrink efficiencies (ASEs) of 58% and 61%, respectively, with a small loss of 3% ASE after four cycles of water swelling and drying treatment. At 26.1% chemical weight gain, the reacted wood lost 5.8% bonded diisocyanate in a 12-week soil-block decay test. Evidence of cross-linking between wood and 1,6-diisocyanatohexane was provided by the characteristic carbamate infrared absorption. In the absence of water, 1,6-diisocyanatohexane reacted with wood to form cross-linking wood as the only product; in the presence of water, diisocyanate reacted preferentially with water to form mainly ureas with a small amount of biurets. These chemicals were deposited in the cell lumen of wood. Water vapor sorption of wood reacted with 1,6-diisocyanatohexane indicated that the decay resistance of this modified wood is probably due to the inability of the modified cell wall of wood to absorb sufficient water to support decay

The Uniformity Factor-a Proposed Method for Expressing Variations in Specific Gravity

Existing measures of uniformity of specific gravity, as obtained by X-ray densitometry, are examined in light of how well they fulfill the requirements thought to be necessary for a uniformity indicator. Based upon an examination of mass and volume specific gravity distributions, a new indicator is proposed. This indicator, the uniformity factor, relates the volume distribution of specific gravity within an increment of wood to a selected reference base. The suitability of the uniformity factor for estimating wood uniformity is shown using data from two species of different uniformities. This approach appears to have potential as a new tool in predicting wood quality

Comparison of Exclusion Values for Lumber Strength

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

Effect of Load Rate on Flexural Properties of Wood-Plastic Composites

With the increase in wood-plastic composite (WPC) products in the commercial marketplace, it is important that the material properties of WPC products are accurately determined. Many of these products are targeted for use in flexural applications; thus the ability to accurately determine the flexural properties is of critical importance if WPC products are to compete as a structural material. Third-point bending tests were conducted on selected WPC formulations at rates ranging from 4.6 mm/min to 254 mm/min and flexural properties were determined. It was found that rate-of-load effects were present for both modulus of rupture and modulus of elasticity over certain ranges of load rate values. Specifically, significant decreases in flexural properties were observed for load rates slower than 62.5 mm/min

Grid-Based Tactile Sensor System for Shrinkage Pressure Measurement

A study was conducted to determine the applicability of a grid-based tactile pressure sensor system in monitoring the shrinkage pressure in wood during drying. The sensor was attached to green red oak (Quercus sp.) and loblolly pine (Pinus taeda L.) boards through a mortise fitted with a two-piece metal insert. As current sensor models could not withstand actual kiln-drying temperatures, the boards were allowed to dry under room conditions (70°F and 60% RH).Results indicate that the pressure sensor system could accurately monitor the shrinkage pressure within the sample boards. Frame-by-frame recordings of the pressure profile across the loaded sensor grids showed not only a visual manifestation of the stress development and reversal phenomena in drying, but also the magnitudes of the internal compressive stresses. For the first time, both real-time visual graphics and quantitative data on compressive drying stresses in wood are made available. The current sensor system is designed exclusively for measuring compressive stresses, and is incapable of monitoring the magnitude of the internal tensile stresses that occur simultaneously with the compressive stresses

Moisture Effects on Load-Duration Behavior of Lumber. Part I. Effect of Constant Relative Humidity

The effect of moisture content on the load-duration behavior for structural lumber is presented. Select Structural and No. 2 Douglas-fir 2 by 4 specimens were tested in bending at relative humidities (RH) of 35%, 50%, and 95% with a constant temperature of 73 F maintained during the tests. Constant loads based on the 15th percentile of the static strength distribution for each grade at 73 F and 50% RH were used to load the beams. The results indicate a trend toward shorter times-to-failure at higher moisture contents subjected to equal mechanical stress ratios. The effect, however, was no more evident in the No. 2 grade specimens than in the Select Structural specimens. Survival rates were likewise reduced at higher humidities