A study is described on the occurrence of wetwood in black cottonwood, found in the Lower Fraser Valley of British Columbia, Canada. Wetwood first appears when trees are 8 to 10 years old, and in 12 year and older trees, wetwood is always present. Further extension of wetwood is similar to that of a normal heartwood, A large number of microorganisms with different 0₂ requirements (i.e., aerobes as well as facultative and obligate anaerobes) were found in the wetwood. Wood-destroying fungi were absent in the wetwood. In the majority of the black cottonwoods examined, very low 0₂ concentrations (<0.1% or microaerobic conditions, detected by a Field-lab 0₂ analyzer) were found in the wetwood during the summer. Generally the 0₂ concentration increased during the winter while the reverse was true for CO₂ (detected by gas chromatography). CH₄ was also present, but only in small quantities, in most trees. Mechanical wounding of wetwood resulted in an increase in the 0₂ concentration and decrease in the CO₂ and CH₄ concentrations. However, sealing of the wound re-established the original gas composition. Presumably the microbial flora of wetwood is primarily responsible for the microaerobic conditions. The ability of 2 wood-destroying fungi (Polyporus delectans Peck and Ganoderma applanation [Pers.] Pat.) to cause a weight loss in wood under microaerobic and aerobic conditions (10 weeks incubation each) was determined, using a soil-block experimental technique, Microaerobic conditions prevented weight loss in wood (average 0.1%) and therefore wood decay, whereas under aerobic conditions, the average weight loss was 41.7%. Special characteristics of wetwood such as high pH (average 7.8) or high moisture content (approximately 160%) did not contribute significantly to the decay resistance. Also, microorganisms associated with wetwood showed no antagonism to the growth of wood-destroying fungi. Exposure of wood-destroying fungi to microaerobic conditions subsequent to aerobic conditions arrested their growth and ability to cause weight loss. On the other hand, exposure of these fungi to aerobic conditions following the microaerobic conditions, induced a significant weight loss in wood (average 10.9%), but it was considerably less than when the fungi were grown under aerobic conditions alone (average 41.7%). The 2 wood-destroying fungi survived 10 weeks exposure to microaerobic conditions, A 13 weeks exposure to anaerobic conditions (<0.002 % 0₂), however, resulted in the death of these, wood-destroying fungi. Eight wood-destroying fungi differed in their abilities to survive under anaerobic conditions; generally brown-rot fungi tolerated anaerobic conditions better than the white-rot fungi. Therefore, if anaerobic conditions exist in the tree trunks for long durations, some fungi (probably white-rot fungi) may die during that period while others (probably brown-rot fungi) may survive such an exposure and resume decay activity when 0₂ becomes available. These findings led to the concept that the microaerobic conditions found in the wetwood of black cottonwood may prevent the development of decay. / Forestry, Faculty of / Graduate

The primary purpose of this study was to measure experimentally the uniaxial (tangential direction) equilibrium moisture profiles in moisture-sealed wood samples subjected to constant but different temperatures T on opposite faces, and to compare these profiles with those predicted by each of several theoretical models. Each test assembly consisted of eight end matched wood laminae, each 0.2 cm thick, for a total thickness of 1.6 cm in the tangential direction. Opposite faces of each moisture-sealed assembly were exposed continuously for approximately five weeks to different but constant temperatures until the original uniform moisture content M redistributed itself to a new constant but non-uniform moisture profile. At moisture equilibrium, the individual wood laminae were removed from the assembly and their moisture contents measured gravimetrically. Both temperature, T vs x, and moisture profiles, M vs x, where x is the distance from the cold face were plotted for each test. The experimental variables considered were wood species (yellow poplar and hard maple), initial moisture content (9%, 12%, and 15%), and temperature range (15°C to 35°C, and 25°C to 45°C). Each condition was replicated 3 or 4 times, giving a total number of 44 different tests. At the steady state, a moisture content profile opposite to the temperature gradient was established. The temperature gradient dT/dx was constant in all cases, with the moisture content profile increasing almost exponentially with decreasing temperature. The absolute magnitude of the calculated ratio dM/dT was found to vary with initial moisture content, temperature range, and species. The Soret coefficient, defined as - ( 1/M )( dM/dT ), was also calculated and was found to vary with the above variables as the dM/dT ratio. These two quantities always increased with wood moisture content. They were also slightly higher at the higher temperature range. There was only a small difference between species, with yellow poplar giving somewhat higher mean values. The Soret coefficient was generally in the range of 0.03 to 0.05 per degree Kelvin, except for the extremely high moisture contents near and above fiber saturation, where the calculated values approached 0.5 per degree Kelvin. The ratio dM/dT was analyzed in terms of five different theoretical models, two of which are based on nonequilibrium thermodynamics (NET) and three on classical thermodynamics. All models require sorption isotherm and heat of sorption data; and in some cases, the activation energy for moisture transport through wood. Adsorption and desorption isotherm data were obtained at 30°C for both species. Heat of sorption and moisture transport activation energy data used in testing the models were taken from the literature. The two NET models provided the best agreement with the experimental values of dM/dT. The Siau model gave the next best prediction, followed by the Stanish model, with the Skaar- Siau model giving the poorest agreement with the experimental results. The heat of transfer was also computed using the two NET models as well as those of Stanish and Siau. Values ranged from 5500 to 17000 cal/mol and from 8100 to 9900 cal/mol based on the Nelson model. The corresponding values for the Stanish for the general NET model and from model range from 15200 to 16500; while those of the Siau model varied between 11700 to 13600 cal/mol. Calculations of other quantities from the information generated in these experiments revealed that at the steady state, vapor pressure and spreading pressure were not constant across the thickness of the material; the chemical potential of water vapor and sorbed water were equal at all points indicating local equilibrium; and that the sorbed water and water vapor entropies were more or less constant across the thickness of the sample. / Ph. D.

Although the drying process can improve the overall quality and usefulness of forest products, if drying is not carefully controlled, drying loss can be substantial. As most drying defects occur when the lumber moisture content is above fiber saturation point (FSP), measurement of moisture content (MC) above FSP is critically important. In this study, a technique was developed which permits use of an electrical resistance moisture meter RDX-1 (Delmhorst Instrument Company) to measure MCs of red oak and yellow-poplar during drying when MC is above FSP. The Lignomat in-kiln probe electrode was used throughout experiments. Two experiments were conducted. The first dealt with developing a two-point technique to measure MC above FSP. The other evaluated the effect of the moisture gradient on the MC reading from the meter. During the drying, pin electrode also was used when oven-dry MC was about 40% in order to compare the MC readings by the pin electrode and the probe electrode. The experimental results show the correlation between the MC readings and oven-dry MC of the sample is quite high during drying; the correlation of each sample is higher than 0.9. Based on this relationship, two-point technique of measuring MC above FSP was developed. This technique can predict MC above FSP of red oak within 5%, and the MC of yellow-poplar within 10%. From the experiment, it was found, when MC is above FSP, MC readings measured by probe electrodes are significantly different from those measured by pin electrodes. It was also found that the moisture gradient affects the MC readings dramatically. The depths of probes inserted into the boards are an important parameter for measuring MC. Different depths yield different MC readings. / Master of Science

In this paper, the application of the diffusion equation to the problem of moisture movement below the fiber saturation point is investigated. The general diffusion equation was solved by numerical methods for the case of a concentration-dependent coefficient and a boundary condition of a specified concentration variation. Experimental concentration-distance curves were generated from the drying of yellow poplar. Solutions to the diffusion equation using coefficients from the literature were then compared with the experimental data. The diffusion coefficient of yellow poplar was determined directly from the concentration-distance curves by the method of Matano. On the basis of the above information, a diffusion coefficient was determined which accurately describes the drying of yellow poplar between 61 and 181 moisture content. / Master of Science

Woody biomass transportation costs and market values/costs are strongly correlated with the woody biomass moisture content. Properly managing moisture content can potentially lead to economic and environmental advantages in biomass energy markets. Good management requires accurate moisture content measurements. Therefore, availability of accurate, precise, reliable, and efficient tools to assess woody biomass moisture content is essential. In this study, six different tools (Fibre-Gen HM200, IML Hammer, Humimeter BLW, Timbermaster, Humimeter HM1 and Wile Bio Meter) were evaluated. The six tools employed three different measurement technologies; acoustic, conductance, and capacitance. Woody biomass samples were collected over one season (summer 2011) at three different locations in western Oregon (Corvallis, Dallas, and Clatskanie) for three softwood species and three hardwood species: Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), Ponderosa pine (Pinus ponderosa L.), western hemlock (Tsuga heterophylla (Raf.) Sarg.), hybrid poplar (Populus spp.), Madrone (Arbutus spp.), and Garryana Oak (Quercus garryana Dougl. ex Hook). Twenty 3-meter long log (20 to 400mm diameter) specimens were collected per species; 18 specimens were divided into two different treatments (open vs. covered), and the two remaining specimens were chipped. In addition, approximately 100 kilograms per species of hogfuel (limbs and tops) were collected and chipped. Moisture content measurements of logs, chips, and hogfuel were made regularly over a four month period. These data was used to develop multiple linear regression models for assessing the moisture content of the six species using the six tools. The major factors considered in the regression models were species (6), treatment (2), and tools (6). The data were also used to estimate the sample size needed for each tool. The best tool from each technology type was identified. The results generated from this study show that (1) none of the tools are accurate without calibration for different species, (2) the best model/tool combination could only explain about 80% of the variability in measurements, (3) further product development is required in some cases to ensure that the tools are robust for industrial application, and (4) there is a wide range in efficiency of the tools (i.e., 50 minute tool efficiency range). The Fibre-Gen HM200 and Wile Bio Meter were the most accurate, precise and efficient tools tested. The cost of transporting woody biomass from the forest to woody biomass plants is "optimized" when the moisture content drops to approximately 30% (wet basis). Validation of the models developed for three of the tools tested (Fibre-Gen HM200, Humimeter BLW and the Wile Bio Meter) indicates that the tools are accurate below 35% MC (wet basis). This suggests they could be used for making threshold transportation decisions, i.e., determining when to haul. / Graduation date: 2013

One of the major processes in lumber industry is wood drying. This process consumes large amounts of energy and capital, and due to the length of time it takes, it acts as a governing factor in lumber production levels. Development of improvements in processes and equipment used in wood drying can be expedited through computer simulation of various drying procedures. These numerical simulations depend on the accuracy of numerical models representing wood transport properties, including functional dependency of liquid permeability through wood with respect to local saturation level. Data available in the literature mainly represent wood permeability properties at fully saturated levels. This is an indication of steady state flow methods used in determining these values which are based on wide spread use of similar methods utilized in studies on fluid flow through soil. This research determines unsaturated wood permeability using transient liquid flow methods that are more representative of actual drying process. Initially saturated wood samples are spun in a low speed centrifuge to induce liquid migration through the cell structures. Transient local moisture profiles along the sample are measured using a scanning gamma ray densitometer. Numerical integration and curve fitting procedures are used to process these data. Finally, utilizing liquid continuity equation the functional dependency of permeability with respect to saturation is calculated. Some permeability results appear to be reasonable when compared with actual wood behavior during drying. Measurement procedures prove to yield accurate results for moisture content and saturation levels in wood with less than 5% relative error in average saturation level of .75. However, due to natural inhomogeneities in wood cellular structure, the final calculated results for unsaturated permeability show high levels of uncertainty (up to 112% relative error).

Previous research on coarse woody debris (CWD) indicated that moisture content and initial heterotrophic colonization of decaying wood can affect the decomposition process. Six heterotrophic treatments were created to simulate the effects of physical penetration of the bark and wood and the transmission of ascomycetes versus basidiomycetes into CWD. In 1995, 360 Douglas-fir (Pseudotsuga menziesii) were randomly placed at five replicate sites in old-growth stands. Each site had 6 heterotrophic (HET) x 2 moisture combinations (TENT). One set of logs representing the treatment combinations was used for sampling respiration and another set was used to measure volume affected by insect gallery excavations and fungal rot and to determine decay rates. Respiration was sampled three times during the summer of 2001. The results indicated that the HET treatments were no longer affecting respiration rates. Analysis of the average of the three sampling periods revealed no TENT effect but examinations of the individual sampling dates suggests that tented logs might have higher respiration rates than non-tented logs as summer progresses. In the aggregate, the TENT treatment reduced moisture content from 45% to 36%, a 20 percent reduction in moisture levels. The HET and the TENT treatments did not affect decay rates. The mean density change for the logs was -0.072 g/cm�� �� 0.03 and the mean decay constant was 0.026 �� 0.011. The TENT treatment did affect heterotrophic activity. The mean volume of wood borer excavation and extent of brown rot was higher in the tented logs (256 cm��) than in the non-tented logs (59.9 cm��). There was also a statistically significant interaction between the HET and TENT treatments. The largest differences in volume affected by wood borers and fungal rot were found in treatments that injected ascomycetes into the experimental logs. In sum, there was limited evidence that the differences in moisture content caused by the TENT treatment affected the decomposition process but the HET treatments appear to not be directly influencing decomposition after six years. The findings suggest differences in the initial community composition of heterotrophs have a decreasing impact on the decomposition process as it progresses. / Graduation date: 2004

The effects of initial particle moisture content, wood-cement ratio and density on physical (thickness swelling and water absorption) and mechanical properties (MOE, MOR, IB and edgewise compression) were investigated. Five initial particle moisture content levels - 0-6%, 8-15%, 25-30%, 40-50% and 60-80%; three wood-cement ratios - 1:1, 1:1.5 and 1:2; and three density levels at each wood-cement ratio - 1:1 -0.472 g/cm³, 0.528 g/cm³ and 0.622 g/cm³, 1:1.5 - 0.636 g/cm³, 0.707 g/cm³ and 0.809 g/cm³; and 1:2 - 0.763 g/cm³, 0.847 g/cm³ and 0.939 g/cm³ were used. Combinations of the above variables gave 45 treatments. Three replicate boards were made for each treatment thus giving a total of 135 panels for the study. A total of 135 test specimens were used for each property tested. Results from the tests were compared to the German and ISO Standards for similar boards and to the Canadian Waferboard Standard. Initial particle moisture content was highly significant in the development of physical and mechanical properties of magnesite cement-bonded particleboard. Increasing initial particle moisture content from 0-6% to 60-80% resulted in the reduction of the physical and mechanical properties of the boards. The highest initial particle moisture content of (60-80%) yielded the lowest physical and mechanical properties. For manufacture of boards of favourable mechanical properties, an initial particle moisture content of not more than 15% is recommended. On the other hand, a higher initial particle moisture content (>40%) is considered desirable if board thickness and water absorption are to be minimized. All the mechanical properties tested consistently increased by increasing wood-cement ratio and density and were highest at 1:2 wood-cement ratio and density level 3 of each wood-cement ratio. Thickness swelling and water absorption were consistently reduced by increasing wood-cement ratio and density. In both physical properties tests, the 1:2 wood-cement ratio and density level 3 yielded the lowest values. Thirty-two of the forty-five treatment combinations of initial particle moisture content, density and wood-cement ratio pass the MOE requirement of the German Standard DIN 52 362 for Portland cement-bonded particleboard; forty-one treatments met the minimum MOE Canadian Waferboard Standard requirements, while no treatment meet the MOR requirements for this Standard. Eleven of the forty-five treatments met the minimum IB Canadian Waferboard Standard requirements. All the 45 treatments pass the ISO building board requirements in thickness swelling, while 18 treatments pass the water absorption requirements for this Standard. Most of the treatment combinations compare favourably with results obtained in tests conducted in Europe for cement-bonded particleboard. / Forestry, Faculty of / Graduate

No description available.

Wood with a uniform moisture distribution is known to have different mechanical properties compared to wood with a non-uniform moisture distribution. Moisture gradients are likely to develop in full-size members tested in the In-Grade Testing Program and might therefore affect the test results. The purpose of this study was to mathematically model the effect of desorption moisture gradients on the stiffness and strength of yellow-poplar beams. An additional objective was to experimentally determine gradient effects in yellow-poplar beams. Three-dimensional finite-element modeling was employed and several subsidiary models were developed. Among these was a three-parameter segmented model for fitting digitized tension and compression stress-strain curves. Unlike previous models (such as the Ramberg-Osgood model), this model has a linear slope up to the point approximately corresponding to the proportional limit. A methodology was also devised whereby most hardwood and softwood elastic constants can be estimated at any moisture content. Data are required at one moisture content. Equilibrated uniaxial testing was conducted at four moisture contents to acquire data for the finite-element model. It was found that the longitudinal Young's moduli in tension and compression were approximately equal at 6% and 18% moisture content; the compression modulus was greater at 12%, but the tension modulus was greater for green specimens. Intersection points for tension and compression mechanical properties may be different. Tests of small clear yellow-poplar beams indicated that moisture gradients induced at 12% equilibrium moisture content had little effect on the modulus of rupture up to 19% average moisture content. At higher moisture contents, gradient-containing beams were significantly stronger than equilibrated beams when comparisons were made at identical moisture contents. Modulus of elasticity data exhibited a similar trend, although differences between equilibrated and non-equilibrated beams were observed below 19% moisture content. The finite-element program was moderately successful in predicting the effects of moisture gradients on the strength and stiffness of yellow-poplar beams. Computer time and storage constraints limited the accuracy of the solutions. Predicted trends were verified by the experimental data. Modeling of full-size lumber indicated that significant moisture gradients will likely influence the stiffness and strength of higher quality lumber. / Ph. D.