Heat transfer from a flowing gas to a fixed bed of dried Dougas-fir wood chips has been studied by a transient method. Hot air at about 130°C flowed upward through 0.2 m dia x 1 m deep beds of commercially prepared wood chips which had been screened for thickness. Four different wood chip sizes were used, which varied in mean thickness from 2.44 to 7.26 mm. The thickest chips were 18.4 mm wide x 36.3 mm long. Gas temperatures were measured at a number of axial positions as the bed temperature rose from its initial temperature of about 20°C. Heat transfer coefficients were calculated by fitting the air temperature profiles to a transient mathemical model for plug flow of gas through a bed of slab-shaped particles with finite internal thermal resistance. The heat transfer model was solved analytically using an approach pioneered by Amundson (10) for fixed beds of spherical particles and based on Rosen's (6,7) function. This solution has not appeared elsewhere in the literature, and is shown to converge to that of Anzelius (1) if the Biot number for the particle approaches zero. Experiments were done at a series of air velocities with four wood-chip thicknesses and with spherical catalyst particles to provide a check on the technique. The effect on heating rate of 30% by volume steam in the incoming air was investigated. For selected experiments, solid temperatures within the wood chips were measured. A correlation of the heat transfer coefficients is presented. Pressure drop was measured as a function of air velocity for different sizes of wood chips at room temperature and the results are compared with predictions of the Ergun equation. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Initiation and maintenance of motion within a pulp suspension is necessary for effective mixing. This requires imposition of forces greater than the network strength and depends on suspension rheology once motion begins. As pulp suspensions display non-Newtonian and solid-like behaviour, studies were conducted using profiled rotors which imposed stress within the body of suspensions contained in cylindrical devices. A concentric cylinder device capable of high torques (85 N-m) and high rotational speeds (524 rad/s) was built to study pulp suspension dynamic behaviour. Most work used a profiled rotor 0.1 m in diameter with baffled housings 0.13 and 0.22 m in diamter. The yield stress of low consistency pulp suspensions were measured with a Haake RV12 Ro-tovisco concentric cylinder viscometer. Semi-bleached kraft pulp was used throughout the study. Some tests were made with stone groundwood and thermomechanical pulps. Yield stress measurements were made for nylon and Spectra-900 fibre suspensions. The yield stress of pulp suspensions, ty, have been measured and correlated with mass concentration (Cm) and volumetric concentration (Cv) over the range 0.4 ≤ Cm(%) ≤ 33. It was found that because of increasing gas content that correlations developed using the mass concentration were inaccurate above approximately 20% Cm. Correlations developed using the volumetric concentration were accurate over the full range tested. For a West-Coast semi-bleached kraft pulp, ty(Pa) = 1.40CV(%)²ֹ⁷². Once rotor motion was initiated, pulp suspensions exhibited two distinct regimes of behaviour. The first was a tangential-cavity regime in which predominantly tangential motion grew to fill the chamber as shear rate increased. When motion reached the outer housing wall a flow transition occurred, likely triggered by flow interaction with the housing baffles. The subsequent post-transition regime was characterized by radial and axial flow that effectively mixed the suspension on both the macroscale and fibre-scale. The flow transition appeared to be what earlier workers reported as the onset of "fluidization". During tangential-cavity flow, phase segregation occurred. Gas present in the suspension collected around the rotor and reduced momentum transfer from the rotor to the suspension. This caused the torque for the pulp suspension to fall below that for water at the same rotational speed, and the cessation of flow development in the chamber. If sufficient momentum transfer was attained to initiate post-transition flow, the chamber contents became effectively mixed. The torque could still fall below that of water depending on the effective density of the suspension in the rotor vicinity. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Changes in wood chemistry could have significant impact on both environmental and economic aspects of the pulp and paper industry. Consequently, a considerable amount of effort has been devoted to altering lignin content and/or modifing lignin monomer composition, a cell wall component whose removal is a major part of the chemical pulping process. Analysis of poplar transformed with a cinnamate 4-hydroxylase (C4H):ferulate5-hydroxylase (F5H) construct confirmed significant increases in the mole percent syringyl lignin in transgenic lines. Further, this study demonstrated significant increases in pulping efficiency from greenhouse grown transgenic trees. Compared to wild-type pulp, decreases of 23 kappa units (residual lignin) and increases of >20 ISO brightness units were observed in tree lines exhibiting high syringyl monomer concentrations (93.5% mol S). These changes were associated with no significant change in total lignin content or observed phenotypic differences in the trees. Additionally, pulp yields were not affected by the enhanced removal of lignin.. Furthermore, transgenic lines exhibit reduced fibre coarseness and increased cellulose viscosity. These results suggest that C4H-F5H transformed trees could be used to produce pulp for paper with substantially less severe delignification conditions (lower chemical loading or less energy), and that the pulp produced is of comparable quality to that of the wild-type poplar. Consequently, the ecological footprint left on the environment, measured by the amount of deleterious pulping by-products released into the environment may be significantly reduced. / Forestry, Faculty of / Graduate

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

Arborists use formulas to estimate the risk of failure in trees with decay. The study investigates the appropriateness of using formulas to determine the risk of tree failure. Two variables were examined, whether trees improve wood toughness in the vicinity of mechanical stress concentrations, and how well the formulas estimate the loss in moment of inertia due to decay. Red maple (Acer rubrum) callus wood toughness was consistently greater than for normal wood, but, in some cases, the formulas significantly underestimated the actual loss in moment of inertia. The improvement of callus wood toughness is not related to increases in mechanical stress on the tree, but instead seems to be related to callus cell anatomy.

Wood composites industry has been growing for decades. However, wood composites have been associated with some health concerns due to the presence of formaldehyde. A promising bio-based resin Epoxidized Sucrose Soyate (ESS) was investigated as a potential primary binder in particleboards. The goal of this research was to find a strong and durable resin for wood composites. Several ESS-MDI based formulas were found that were able to match the performance criteria for particleboard. / North Dakota Soybean Council

archives@tulane.edu / 1 / Blas Isasi gutiérrez

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Although incipient fungal decay of wood may be difficult to detect early, it causes a significant decrease in wood strength. Developing a reliable method of decay identifica-tion to overcome wood replacement costs by non-destructive methods is necessary. This study investigates a possibility of identifying fungal volatile organic compounds (VOCs) as means of fungal detection using solid phase micro-extraction (SPME) coupled with gas chromatography–mass spectrometry (GC-MS). Volatile emissions from two brown rot (Gloeophyllum trabeum and Postia pla-centa) and two white rot (Trametes versicolor and Irpex lacteus) fungi on pine and aspen and their profiles related to wood mechanical strength and mass loss were investigated over 12 weeks. Principal component analysis of VOCs spectra differentiated volatiles from decayed and sound wood. Volatiles from two fungal species revealed distinct pat-terns of early and late degradation stages. SPME combined with GC-MS showed promissing results for non-destructive identification of incipient decay in wood struc-tures.