Effect of Moisture on Bending and Breaking Resistance of Commercial Oriented Strandboards

This is a short addendum to an earlier paper (Wu and Suchsland 1997) on bending resistance (E·I) and breaking resistance (R·S) of commercial oriented strandboard (OSB). It is shown that for a moisture content (MC) change from 4 to 24%, the combined effect of increased MC and thickness swelling led to an average E·I loss of 37% in the parallel direction and 51% in the perpendicular direction; and to an average R·S loss of 31% in the parallel direction and 43% in the perpendicular direction. Predictive equations expressing E·I and R·S as functions of moisture content were established for various products

Prediction of Moisture Content and Moisture Gradient of An Overlaid Particleboard

Equilibrium moisture contents (EMCs) and diffusion coefficients of a high pressure laminate (HPL) overlay, a wood particleboard (PB) substrate, and an HPL backer (BCK) were measured at different levels of relative humidity (RH). The EMCs as a function of RH were fitted to the Nelson's sorption isotherm. It was found that Nelson's model reproduced accurately the experimental data of these different materials. Over a given RH interval, the PB face layer had a smaller diffusion coefficient than the core layer. Diffusion coefficients for both PB face and core layers decreased with increase in moisture content (MC). For overlays, diffusion coefficients increased with MC for both HPL and HPL backer.A model based on the diffusion theory was developed to predict MC and moisture distribution for a multi-ply wood composite panel. The model's prediction of the mean MC for a three-layer PB, a two-ply HPL+PB panel, and a three-ply HPL+ PB+BCK panel compared favorably with experimental data. Developments of asymmetric moisture distributions within the HPL+PB and HPL+PB + BCK laminates were demonstrated, and their implication for the panel's warping potential was discussed

Surface Characterization of Chemically Modified Wood: Dynamic Wettability1

Dynamic wettability of chemically modified yellow-poplar veneer was investigated with sessile water droplets in this study. Dynamic contact angle, decay ratio, spreading ratio, and their changing rates (the wetting slope and K value) were used to illustrate the dynamic wetting process. Dynamic contact angle (α) and droplet height decay ratio (DRh) followed the first order exponential decay equation, whereas the droplet base-diameter spreading ratio (SRφ) fitted the Boltzmann sigmoid model. Wetting behavior of Epolene G-3015 [a maleated polypropylene (MAPP) copolymer with a high molecular weight]-treated wood surface was independent of the retention and wetting time. The retention effect on wetting slopes of >, DRh, and SRφ on poly(ethylene and maleic anhydride) (PEMA)-treated specimens was opposite to that on Epolene E-43 (a MAPP copolymer with a low molecular weight)-treated specimens. Based on these two models, the wetting slope and K value were used to interpret the kinetics of wetting. Therefore, these methods were helpful to characterize the dynamic wettability of wood surfaces modified with different coupling agents

Surface and Interfacial Characterization of Wood-PVC Composite: Imaging Morphology and Wetting Behavior1

An imaging technique was used to investigate wetting behavior of wood-PVC composites in this study. Two-dimensional and time-dependent profiles of water droplets on maleated wood surface and wood-PVC interface were observed. Experimental results indicated that coupling agents Epolene E-43 (a maleated polypropylene copolymer with low molecular weight)- and polyethylene-maleic anhydride (PEMA)- treated veneers had a hydrophilic surface, whereas the coupling agent Epolene G-3015 (a maleated polypropylene copolymer with high molecular weight)-treated veneer had a hydrophobic surface. For E-43- and PEMA-treated veneers, a water droplet had an elliptical shape after initial contact with the wood surface. However, a sessile droplet on G-3015-treated specimens was closer to a circular shape. During wetting, contact angle changes on E-43- and PEMA-treated specimens were larger than those on G-3015- treated specimens. Contact angles on maleated specimens with heat treatment and maleated interphases were almost independent of wetting time. Initial contact angle was influenced by coupling agent type, acid number, and retention and directions of wood grains. Initial contact angle decreased with increase of E-43 retention, but it was proportional to PEMA retention. However, it was independent of G-3015 retention. Wettability of fractured wood-PVC interface was similar to that of maleated wood surface with heat treatment. Thus, the interfacial characteristics of wood-PVC interface can be simulated with maleated wood surface with heat treatment

In-Plane Dimensional Stability of Three-Layer Oriented Strandboard

In-plane swelling and bending properties of three-layer oriented strandboard (OSB) were investigated under the interactive influence of flake alignment level (FAL), flake weight ratio (FWR), resin content (RC), vertical density gradient, and moisture content (MC) levels. Mathematical models based on lamination theories were developed to predict effective modulus (EM), linear expansion (LE), and internal swelling stresses. The model's prediction was compared with actual experimental data.It was shown that the relationship between LE and MC change for OSB was curvilinear with larger expansion rates at lower MC levels. FAL and FWR were two primary variables that significantly affected the magnitudes of LE, modulus of elasticity (MOE), and modulus of rupture (MOR). Increase in RC from 4% to 6% led to little change in all three properties.The model predicted general trends of change in LE, EM, and swelling stresses as a function of FWR at the two alignment and two RC levels. The model's prediction in both EM and LE compared favorably with the experimental data. Prediction of the in-plane swelling stresses showed the effect of the panel MC change and directional dependency. The model provides an analytical tool for optimizing flake alignment level and panel flake weight ratio to achieve a proper balance between EM and LE for OSB manufacturing