Wood and Fiber Science (E-Journal)
Not a member yet
2592 research outputs found
Sort by
Effects of Environmental Factors on Decay Rates of Selected White- and Brown-Rot Fungi
Get PDFAssessing the impact of fungal decay in wood structures poses a major challenge for building inspectors. Although models have been developed to predict degradation rate of building components in varying climatic conditions, most are hampered by the lack of fundamental data on effects of fungal attack on engineering properties. Developing data on degradation rates in differing conditions would help enhance these models. The ability of two brown-rot and one white-rot fungus to degrade wood of three species was assessed in varying temperature and moisture conditions. Modulus of elasticity (MOE) was the most sensitive measure of fungal attack, whereas modulus of rupture (MOR) was affected more slowly. Wood species had no effect on MOR losses, but wood durability did influence fungal effects on MOR. The white-rot fungus caused comparable MOE losses to the brown-rot fungi but had a much decreased effect on MOR. Moisture content, within the range tested, had little influence on decay rates. Fungal effects tended to be slower at the lowest temperature tested (15°C) but differed little between 25 and 35°C. Results suggested that removal of wood that has been wet for some time is advisable if dynamic properties are critical. Results also supported incorporating temperature and time of wetting factors into building models
Chemical Composition of Cork from Quercus Variablis
Get PDFCork is a natural and renewable raw material harvested from the outer bark of oak (Quercus spp.) trees. Unique and valuable properties of cork include low density, low permeability, high elasticity, good heat and acoustic insulation properties, and resistance to chemical and microbial attack. Chemical composition of cork is affected by many factors including the Quercus species and the number of times that cork has been harvested from the tree (ie virgin vs reproduction cork). Differences in chemical composition can significantly influence cork properties. In this study, chemical composition of virgin and reproduction cork from Quercus variablis trees in Shaanxi Province, China, was investigated. Cork samples were sequentially extracted with dichloromethane, ethanol, and water in a Soxhlet extractor. Eluted fractions were analyzed using ion chromatography. Chemical composition of virgin Q. variablis cork was 34.3% suberin, 20.6% lignin, 17.4% extractives, and 15.2% polysaccharides. Composition of reproduction cork was 36.9% suberin, 19.9% lignin, 12.7% extractives, and 12.0% polysaccharides. These results show that composition of virgin and reproduction Q. variablis cork was similar. Virgin Q. variablis cork had greater extractives and polysaccharides content than reproduction cork but a little less suberin. Chemical composition of Q. variablis cork from China is significantly different from that of Quercus suber L. cork from Europe
Moisture Properties of Heat-Treated Scots Pine and Norway Spruce Sapwood Impregnated with Wood Preservatives
Get PDFAn experiment was conducted on commercially heat-treated (HT) Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies [L.] Karst.) sapwood collected from Ht Wood AB, Arvidsjaur, Sweden. Secondary treatment on HT wood was performed in laboratory scale by impregnating with water-repellent preservatives (a commercial one and pine tar) to evaluate their retention and different moisture-related properties. Preservative solutions were impregnated using a simple and effective method. Wood samples were heated at 170°C in a dry oven and were immediately immersed in preservative solutions. Considerable retention was observed in HT wood, particularly in pine. Moisture adsorption properties were measured after conditioning in a high-humidity environmental chamber (4°C and 84% RH). Experimental results showed that secondary treatment enhanced moisture excluding efficiencies by decreasing equilibrium moisture content, suggesting better hydrophobicity. Soaking test in water showed that antiswelling and water repellence efficiencies improved, especially in tar-treated wood. In addition, this type of treatment significantly decreased water absorption. It was also possible to decrease volumetric swellings. Thus, secondary treatment of HT wood with preservative, in particular with tar, improved dimensional stability and water repellency
Numerical Modeling of the Medium-Density Fiberboard Hot Pressing Process, Part 2: Mechanical and Heat and Mass Transfer Models
Get PDFIn this study, coupled mechanical and heat and mass transfer models describing mat compression and heat and moisture transfer occurring during hot pressing of medium-density fiberboard mats are presented. The mat is considered an aging linear elastic material and is described by a mechanical model in three dimensions. Rheological properties of the mat depended on time, space, temperature, moisture content, and resin cure. Hardening and softening phases of the material behavior were accounted for and treated with separate constitutive laws. Press closing was taken into account, and a coupling procedure between mechanical and heat and mass transfer models was elaborated. Development of the vertical density profile was dynamically predicted by the model. Both mechanical and heat and mass transfer models were discretized in space by the finite element method. An implicit second-order backward finite difference scheme was used for time discretization. All calculations were carried out on a moving geometry whose deformation (compression) was a function of a press closing schedule. Model results exhibited good agreement with experimental results. Under various press closing schedules, the model gave information on variables such as density profile, total gas pressure, air and vapor pressure, temperature, moisture content, RH, and degree of resin cure
Bowtie Beams: Novel Engineered Structural Beams from Southern Pine Lumber
Get PDFThe intersection of decreasing resources and increasing population and its associated demands creates a need to develop alternative products to solid sawn lumber. This research used a modified form of sawn southern pine (SP) lumber in which cants were sawn into symmetrical double-trapezoidal shapes and glued together to form a bowtie beam. The result was a cross-sectional shape that was widest at the beam flanges and narrowest at the neutral axis. Cants were cut from logs and sawn into trapezoids, nondestructively tested, glued into the bowtie beams, and nondestructively and destructively tested to determine mechanical values as per ASTM D4761. The objectives of this study were to manufacture composite bowtie beams and to conduct nondestructive and destructive testing on the beams. Overall, the bowtie beams compared favorably with strength properties of No. 2 SP lumber of roughly equivalent size to the bowtie beams. The bowtie beam shows promise as an engineered product because a minimal amount of capital and technology is needed to process small-diameter trees into this value-added product
Predicting Load-Carrying Capacity of Dovetail Connections Using the Stochastic Finite Element Method
Get PDFThe goal of this study was to evaluate the load-carrying capacity of dovetail connections. Different tenon angles (θ), tenon neck widths (w1), tenon head widths (w2), and tenon heights (h) were used to analyze stress distribution and strength from dovetail connections using the finite element method (FEM). Although different stress distributions were found from the FEM models, shear and tension perpendicular to the grain stresses were found to be the most critical stresses controlling strength of the dovetail connection. Strength of the dovetail connection predicted from the deterministic FEM models was validated from the results of experimental tests. A combination of four geometric parameters for mortise and tenon from the dovetail connection maximizing load-carrying capacity was found. Allowable load-carrying capacity of the dovetail connection was estimated using the stochastic finite element method associated with allowable stress design and load resistance factor design concepts
Effect of Microcrystalline Cellulose, Species, and Particle Size on Mechanical and Physical Properties of Particleboard
Get PDFParticleboards made from both sweetgum (Liquidambar styraciflua) and southern pine (Pinus spp.) were made at a small and large particle size and at 0 and 10% microcrystalline cellulose loading. Modulus of rupture, modulus of elasticity, work to maximum force, and thickness swell (after 2 and 24 h) were measured for all treatment combinations. An increase in particle size had a positive influence on mechanical properties but also allowed for more thickness swell, particularly for the southern pine furnish. Conversely, adding cellulose actually decreased mechanical properties, increased thickness swell, and decreased springback. In the field, the ability to manipulate particle size to control particleboard mechanical properties is perhaps more cost-effective and practical than cellulose addition. Replacing southern pine with sweetgum was viable with equal or better mechanical and physical properties. This suggests that the hardwood species could be a feasible substitute for pine as the demand for woody resources in the southern US continues to grow
Spray-Drying Cellulose Nanofibrils: Effect of Drying Process Parameters on Particle Morphology and Size Distribution
Get PDFSpray-drying was chosen as an appropriately scalable manufacturing method to dry cellulose nanofibril (CNF) suspensions. Spray-drying of two different types of CNF suspensions—nanofibrillated cellulose (NFC) and cellulose nanocrystals (CNC)—was carried out using a laboratory-scale spray dryer. Effects of three spray-drying process parameters on particle morphology and particle size distribution were evaluated: 1) gas flow rate; 2) liquid feed rate; and 3) suspension solids concentration. Particle morphology was characterized by scanning electron microscopy (SEM) and a morphology analyzer. SEM showed that spray-drying of NFC formed fibrous particles and fibrous agglomerates, whereas spray-drying CNCs produced spherical and mushroom cap (or donut)-shaped particles. Particle morphology formation mechanisms are proposed for spray-drying nanocellulose suspensions. The effect of the three spray-drying process parameters on particle size distribution depended on the drying nature of the materials. The three parameters interacted to significantly affect particle size of CNC suspensions, whereas they did not interact to affect particle size of NFC suspensions. For the CNC suspension, a higher gas flow rate produced smaller particle sizes. The gas flow rate did not affect particle size for NFC suspensions. The effect of liquid feed rate and solids concentration on CNF particle size was negligible in this study. The smallest mean circle equivalent diameters produced in this study were 3.95 μm for NFC and 3.64 μm for CNC
