Stephen M. Shaler

Comparing two measures of flake alignment

SummaryAlignment of particles in structural composites is desirable to increase the strength and stiffness of the panel in one direction. The magnitude of resulting orthotropic panel properties are influenced by the degree of alignment. Quantification of the degree of alignment in the literature has primarily been attained by a parameter known as percent alignment. Measures of flake alignment in probability distribution form have received some, though more limited attention. However, use of statistical distributions to describes particle orientation, such as that provided by the von Mises distribution are needed for simulations of composite panel properties. It is shown that percent flake alignment is a linear transformation of the first moment (arithmetic mean) of the absolute value of angles in the range ±90 degrees. Assuming the von Mises distributional form accurately measures flake alignment, this implies that percent flake alignment is a measure of both the variability in flake direction and the mean flake angle. The numerical relationship of percent alignment with mean angle and variability is presented with a look-up table provided for converting between the two systems of measure. The relation will permit verification of models which employ the von Mises distribution to describe flake alignment using information in the literature based on percent flake alignment. A computer program is available from the author which will calculate percent alignment and distribution parameters for an experimentally obtained samples of angles.

Urea-melamine-formaldehyde (UMF) resin penetration in medium-density fiberboard (MDF) wood fibers

Confocal microscopy has been used to investigate the behavior of urea-melamine-formaldehyde (UMF) resin after being sprayed onto wood fibers. Samples of wood fibers were dyed with Toluidine Blue O (TBO) to create a contrast between the resin and the fiber when studied under a confocal laser scanning microscope (CLSM). The resin droplet penetration into the fiber cell wall was evaluated from the three-dimensional images generated by the CLSM. Experimental conditions were varied to determine their influence on the penetration of the resin into the cell wall. The Washburn equation was used to model the penetration process. The model takes into account variations of the resin viscosity with temperature and time. The penetration rate was found to be related to resin viscosity. The penetration depth can be as low as 1 μm if the resin is applied on a dry spruce fiber in a drum mixer. The maximum penetration depth corresponds to the thickness of the cell wall, which can vary from 10 to 20 μm for spruce. Further work should lead to the development of a more effective resin that could be used to make boards with the same performance but less resin.

Comments on the experimental methodology for determination of the hygro-mechanical properties of wood

Abstract When wood is subjected simultaneously to load and moisture content changes below the fiber saturation point, the mechano-sorptive effect may be observed as an additional deformation that cannot be attributed to simple superposition of elastic deformation, free shrinkage or swelling, or creep in steady climate conditions. The phenomenon has been subject to research for more than half a century. Although numerous mathematical models and detailed theoretical descriptions have been proposed over time, the basic mechanism of mechano-sorption has remained unclear, the experimental data are scattered and lack logical classification, and the experimental determination of its basic parameters on a material level, understood as a local property decoupled from artifacts of the testing protocol, remains a serious challenge. In this paper basic requirements for adequate experimental methods for comprehensive determination of the mechano-sorptive behavior of wood are proposed and briefly discussed. The principal requirements are that the experimental research on mechano-sorption is focused on the material level properties and elementary loading modes (tension and compression); that proper attention is paid to the effect of changing distribution of moisture content within the tested volume; and that the tests are designed so that a comprehensive separation of strain components is enhanced.

Influence of hot-water extraction on ultrastructure and distribution of glucomannans and xylans in poplar xylem as detected by gold immunolabeling.

Abstract Pre-extraction of hemicelluloses from lignocellulosic feedstock has been a research focus during the last decade within the context of lignocellulosic biorefineries. In this study, the effect of hot-water extraction (HWE) on the topochemistry and ultrastructure of poplar wood (Populus sp.) was investigated based on scanning electron microscopy (SEM) and transmission electron microscopy (TEM) paired with immunogold labeling of the hemicelluloses. The cell walls of HWE wood (HWEW) differ significantly in their ultrastructure from neat wood, i.e., there are many distorted cells and agglomerations of lignin and extractives agglomerations in the cell lumina. Results of immunogold labeling indicate that different types of hemicelluloses are extracted at different stages and both their concentration and distribution within the wood cell wall layers are affected by the HWE. Hemicelluloses more closely associated with lignin appear to be more easily removed by HWE. Lignins are also extracted partially and altered. Results provide a holistic view of chemical and ultrastructural changes including the associated changes in hemicelluloses and lignin distribution in HWEW. The obtained data could be helpful to understand better the mechanical properties and adhesion related issues of HWEW for wood composite production.

Moisture movement in wood polypropylene composites.

AbstractMoisture movement in an extruded wood polypropylene composite was evaluated by exposure to high humidity and immersion of the material in both fresh and seawater. The saturation moisture content was approximately 20 and 19% when exposed to distilled water and seawater, respectively. The moisture diffusion coefficient (Dm) of thin specimens exposed to high humidity was 3.4 × 10−8 cm2

Mechanical Property Characterization of Fiber-Reinforced Polymer Wood-Polypropylene Composite Panels Manufactured Using a Double Belt Pressing Technology

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ENHANCING DIMENSIONAL STABILITY OF ORIENTED STRAND COMPOSITES WITHIN BIOREFINERY

s. The Dm of small cubic specimens with extruded surfaces removed submerged in distilled water and seawater were estimated to be 3.1 and 2.3 × 10−8 cm2