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

Effect of Moisture on The Flexural Properties of Commercial Oriented Strandboards

Moisture content (MC), thickness swelling (TS), and bending properties of five commercial oriented strandboards (OSBs) made of two wood species were measured. The measurements were made after specimens were conditioned to equilibrium at 35, 55, 75, 85, 95% relative humidity (RH) and 24°C. It was shown that bending modulus of elasticity (MOE) and modulus of rupture (MOR) decreased with increases in board MC. Both MOE and MOR followed a linear relation with MC over the given MC change. Thickness swelling of these OSBs was shown to have a large nonrecoverable component, which mainly occurred with MC increases above the 8 to 10% level. For an MC change from 4 to 24%, the combined effect of increased MC and TS led to an average MOE loss of 72% in the parallel direction and 83% in the perpendicular direction; and to an average MOR loss of 58% in the parallel direction and 67% in the perpendicular direction. Predictive equations expressing the bending MOE/MOR and thickness swelling as a function of MC and MOE/MOR loss as a function of thickness swelling were established for various products

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

Mechano-Sorptive Deformation of Douglas-fir Specimens Under Tangential Tensile Stress During Moisture Adsorption

Small specimens (3.2-mm thick) of Douglas-fir heartwood were tested for mechano-sorptive (MS) deformation in tangential tension during moisture adsorption. Tests were made at 65.5° with moisture content (MC) changing from 5 to 20% under four levels of stress: 0.276, 0.552, 0.827, and 1.24 MPa. The results confirmed that a large MS deformation occurs during the first MC increase after the load is applied. In a sorplion history of matched loaded and load-free specimens, the MS strain was shown to be proportional to applied stress, and the material parameters describing the interaction of stress and moisture change were independent of stress level

Mechano-Sorptive Deformation of Douglas-fir Specimens Under Tangential Tensile Stress During Moisture Adsorption

Small specimens (3.2-mm thick) of Douglas-fir heartwood were tested for mechano-sorptive (MS) deformation in tangential tension during moisture adsorption. Tests were made at 65.5° with moisture content (MC) changing from 5 to 20% under four levels of stress: 0.276, 0.552, 0.827, and 1.24 MPa. The results confirmed that a large MS deformation occurs during the first MC increase after the load is applied. In a sorplion history of matched loaded and load-free specimens, the MS strain was shown to be proportional to applied stress, and the material parameters describing the interaction of stress and moisture change were independent of stress level