Treesearch

The first models used to describe electrical conduction in cellulosic materials involved conduction pathways through free water. These models were abandoned in the middle of the 20th century. This article re-evaluates the theory of conduction in wood by using a percolation model that describes electrical conduction in terms of overlapping paths of loosely bound or capillary water (Type II water). The model contains two physical parameters: w[subscript]c, the critical moisture fraction, which is the amount of water required to form a continuous path of Type II water in wood; and [sigma]c,...

Accelerated leaching methods are needed to better estimate emissions from treated wood used above ground or above water. In this study, we evaluated leaching methods using continuous immersion, dip immersion, and simulated rainfall approaches. Copper and/or boron emissions were measured for specimens treated with either chromated copper arsenate Type C (CCA-C) or a borax-copper (BC) preservative. The results of these leaching tests were compared with the extent of wetting and drying within the specimens and with the published reports of leaching and MC under natural exposures. Release per...

Spent sulfite pulping liquor (SSL) contains lignin, which is present as lignosulfonate, and hemicelluloses that are present as hydrolyzed carbohydrates. To reduce the biological oxygen demand of SSL associated with dissolved sugars, we studied the capacity of Pichia stipitis FPL-YS30 (xyl3[delta]) to convert these sugars into useful products. FPL-YS30 produces a negligible amount of ethanol while converting xylose into xylitol. This work describes the xylose fermentation kinetics of yeast strain P. stipitis FPL-YS30. Yeast was grown in rich medium supplemented with different carbon...

We have had the opportunity to subject cross-machine paper strips from two mills to both ultrasound and optical "fiber-orientation" tests to examine the relationships between the results. Both determine an orientation angle, in degrees. Both measure sheet anisotropy as an MD/CD orientation ratio. The optical test has no counterpart to the ultrasonic test’s ability to measure MD and CD tensile stiffness index (TSI). On the other hand, the optical test can measure orientation separately on each side of the sheet, and possibly at several depths, while the ultrasonic test produces measurements...

Eucalyptus species are native to Australia but grown extensively worldwide as short rotation hardwoods for a variety of products and as ornamentals. We describe their general importance with specific emphasis on existing and emerging markets as energy products and the potential to maximize their productivity as short rotation woody crops. Using experience in Florida USA and similar locations, we document their current energy applications and assess their productivity as short-term and likely long-term energy and related products.

The challenges of reducing gate leakage current and dielectric breakdown beyond the 45 nm technology node have shifted engineers’ attention from the traditional and proven dielectric SiO2 to materials of higher dielectric constant also known as high-k materials such as hafnium oxide (HfO2) and aluminum oxide (Al2O3). These high-k materials are projected to replace silicon oxide (SiO2). In order to address the complex process integration and reliability issues, it is important to investigate the mechanical properties of these dielectric materials in addition to their electrical properties....

The standard Oliver–Pharr nanoindentation analysis tacitly assumes that the specimen is structurally rigid and that it is both semi-infinite and homogeneous. Many specimens violate these assumptions. We show that when the specimen flexes or possesses heterogeneities, such as free edges or interfaces between regions of different properties, artifacts arise in the standard analysis that affect the measurement of hardness modulus. The origin of these artifacts is a structural compliance (Cs), which adds to the machine compliance (Cm), but unlike the latter, Cs can vary as a function of...

Paper materials consist of a porous web of cellulose polymeric fibers held together by entanglement and fiber-to-fiber bonding. These materials usually contain lignin and hemicellulose carbohydrates remaining from the pulping process. Pulped fibers are a flattened ribbon shape on the order of 30 microns wide, 10 microns thick and from one to four mm long. Paper web porosity typically varies between 30 and 60% by volume. All of these features increase the anisotropy and non-homogeneity of paper materials and complicate the characterization of mechanical properties. The z-direction modulus...

A recently described plant cell wall dissolution system has been modified to use perdeuterated solvents to allow direct in-NMR-tube dissolution and high-resolution solution-state NMR of the whole cell wall without derivatization. Finely ground cell wall material dissolves in a solvent system containing dimethylsulfoxide-d6 and 1-methylimidazole-d6 in a ratio of 4:1 (v/v), keeping wood component structures mainly intact in their near-native state. Two-dimensional NMR experiments, using gradient-HSQC(heteronuclear single quantum coherence)1-bond 13 C-1H correlation spectroscopy, on nonderivat...

The introduction of short, tilted rods to reinforce polymer composite laminates has resulted in near doubling the strength of lap shear specimens. Paperboard is predominantly a multi-layered structure, similar to composite laminates in many ways. Improved bonding between layers should have a positive influence on mechanical performance. Tilted fibers, or z-direction oriented fibers, can improve performance by bonding non-adjacent plies. Presence of fiber tilt should enhance shear and compression behavior without additional fiber. Our goal in this work was to test for the existence of fiber...