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Commercial medium-density fiberboard (MDF) products, specifically manufactured for water resistance, were evaluated over 8 days under three water exposure regimes: 90 percent relative humidity, one-sided water spray, and one-sided wet pad. A three-cycle wet-pad and drying exposure test was also performed. Rate of swelling, extent of swelling, and irreversible thickness swelling were determined. Acetylated MDF (AMDF) had the best overall performance, followed by steam-injection pressed MDF (SMDF) and polymeric methylene-diphenyl-diisocyanate--bonded moisture-resistant MDF. The fastest rate of thickness swell and linear expansion occurred with exposure to one-sided water spray and the slowest with 90 percent relative humidity exposure. While AMDF was clearly superior after 24-hour exposure, the other MDF products were nearly identical. Significant difference in thickness swell and water absorption between moisture-resistant MDF and SMDF developed after 24 hours. Regardless of the method of water exposure, the trend of best to worst MDF performance was the same., Resistance to water, in particular, dimensional stability in the presence of changing moisture environment, is a desirable characteristic for medium-density fiberboard (MDF). Water resistance is important for interior products, such [...]

Development of moisture gradients within wood and wood-based composites can result in irreversible moisture-induced damage. Accelerated weathering (AW), generally employing harsh environmental conditions, is a common tool for assessing moisture durability of wood composite products. Use of milder AW conditions, such as cyclic changes in relative humidity (RH), may be of interest to the wood-based composites industry in assessing moisture durability under more realistic conditions. The primary objective of this study was to determine whether moisture profile development in oriented strand board and plywood during cyclic RH changes could be reasonably predicted with a simple moisture transport model, which may be practical for wood-based composite industry members seeking to develop new AW protocols. The diffusion model based on Fick's second law with empirically determined moisture transport parameters fits the experimental data reasonably well for the purpose of screening RH parameters., As hygroscopic materials, wood-based composites exchange moisture with the surrounding environment. Rapid changes in external conditions or differing climates on opposing faces lead to moisture gradient formation within the cross [...]

Moisture intrusion can be significantly higher along specimen edges, particularly at edges where longitudinal grain is exposed, which is referred to as the edge effect. The influence of edge effects on moisture durability are assumed to decrease as the edge area to total-surface-area ratio decreases. Moisture durability assessment of laminated veneer lumber (LVL) is commonly evaluated using accelerated weathering (AW) and outdoor exposure methods, where small specimens are analyzed. The influence of specimen size (i.e., edge effect) on moisture durability evaluation of LVL was investigated in this study. To vary specimen size, three widths with constant length and thickness were evaluated. In addition, three AW methods were used to characterize how the method of inflicting degradation influenced edge effects. No consistent trends in mechanical property loss were found across AW methods, indicating that the influence of specimen size varied with AW method. The greatest influence of specimen size occurred when cyclic vacuum-soak-dry was included, where water absorption decreased significantly with increasing width, and three of four mechanical properties evaluated displayed an influence of specimen size. The smallest influence of specimen size occurred when a single soak-dry procedure was included, where only one of four mechanical properties evaluated displayed an influence of specimen size. Results from this study provide evidence that edge effects may occur during LVL moisture durability assessment but that the severity is dependent on AW conditions., Laminated veneer lumber (LVL) is an engineered wood composite in the structural composite lumber (SCL) category (APA 2010). LVL is produced by laminating multiple layers of rotary-peeled veneer with a [...]

Abstract The potential for using pretreatment with cinnamon leaf oil or juniper foliage oil to improve the durability of viscoelastic thermal compression (VTC)-treated hybrid poplar was explored in a field [...]

Abstract To produce a highly stable wood-based product with increased mechanical properties, various types of chemical modifications were combined with the viscoelastic thermal compression (VTC) process. Dimensional stability and bending [...]

Abstract Product quality and cost efficiency continue to grow in importance for the wood-based composites industry. The complex dynamics of the manufacturing process lends itself to the adoption of simulation [...]

Abstract This research considered how flake thickness, flake alignment, and changing mat density during consolidation influences oriented strandboard mat permeability, through its thickness and in the plane of the panel. [...]

Unlike constant moisture effects on the behavior of composite materials, transient moisture effects are not well studied and known. Armstrong and Kingston have shown that the creep of wood under transient humidity levels could be greatly accelerated over that at any constant moisture content. Later this phenomenon was termed "mechano- sorptive". In this paper, the authors show that aramid fibers (Kevlar® 29, Kevlar® 49, and Kevlar® 149) and Kevlar® 49/epoxy composites exhibit mechano-sorptive phenomenon. Kevlar® composites were studied using both creep and dynamic mechanical analysis while undergoing desorption. Creep of single Kevlar® fibers was studied during relative humid ity conditions cycled between 5 % and 95 %. The results observed with Kevlar are consis tent with those reported for other natural polymeric materials.

An optimum amount of adhesive penetration is desirable for economy of production and development of bond strength in wood composites. A general method that allows quantitative measurement of gross adhesive penetration in wood is described. Staining techniques have been developed that can provide sharp contrast between a cured adhesive and the wood substrate using fluorescence microscopy. An image analysis system utilizes this contrast to quantify gross adhesive penetration in wood. An example of this technique is provided, whereby the effect of molecular weight distribution of phenol formaldehyde prepolymers on gross adhesive penetration into yellow poplar (Liriodendron tulipifera) flakes is observed and quantified. Adhesive penetration into wood flakes was shown to be correlated with the molecular weight distribution of the prepolymer, decreasing with higher weight average molecular weight. Gross adhesive penetration into hardwoods is likely to be dominated by flow into vessel elements, as demonstrated by the wood species studied here.