Outdoor exposure tests of structural laminated veneer lumber I: evaluation of the physical properties after six years

To investigate the durability of structural laminated veneer lumber (LVL), outdoor exposure tests have been conducted since 1990 at a field-testing site at the Forestry and Forest Products Research Institute. This paper is an interim report on the results after 6 years' exposure. Seven kinds of structural LVL with no preservative treatment were subjected to the tests. These specimens were sampled at the testing site each year and then stored for more than 1 year in a testing room conditioned at 20°C and 65% relative humidity. We then measured the modulus of elasticity (MOE) by longitudinal vibration frequency, the penetration depth by the Pilodyn method, weight loss, color difference (E ^*) by the CIEL ^* a ^* b ^* system, swelling, compression strength, and bending-shear strength. Deterioration caused by outdoor exposure was obvious in the color, weight, MOE, and compressive strength of LVLs, but not in the penetration depth by the Pilodyn method or the bending-shear strength. The retention values of MOE and compressive strength after 6 years of exposure were 78% and 77%, respectively. The difference in durability among material species was not significant in general, except that heavy decay by brown rot fungi took place on some of the grand fir specimens. It should be noted that no significant delamination occurred in any of the adhesive layers, although slight checks developed on the surface of the specimens.     

Study of the release in water of chemicals used for wood preservation. Effect of wood dimensions

Summary Various chemicals are used for protecting wood samples against fungi, and some of them are released in water, leading to pollution of the water. The kinetics of pentachlorophenol release in water has here been studied by considering the diffusion through the wood along the three principal axes of diffusion. The experiments and the modelling of the process is successfully coupled. The numerical model takes into account the three principal diffusivities, the partition factor, the volumes of wood and water. The effect of wood sample length along the longitudinal axis of diffusion is studied especially, as longitudinal diffusivity is much higher than the other two principal diffusivities. The effects of the relative volumes of wood and water are also of considerable interest not only for the concentration of the chemical in water but also for the rate of release.Symbols C concentration of liquid (g/cm³)_ - C _c ,C _eq concentration of liquid on the surface, at equilibrium with the surrounding, respectively - C _i,j,k concentration of liquid in the wood at positioni, j, k - D diffusivity (cm²/s) - h coefficient of mass transfer on the surface (cm/s) - K partition factor - i, j, k integers characterizing the position in the wood - M _L ,M _R ,M _T dimensionless numbers - M _t ,M amount of chemical released after time t, after infinite time, respectively - t increment of time - L, R, T thickness of the slices taken in the wood for calculation - N _L ,N _R ,N _T number of slices taken in the wood - x, y, z coordinates - V _water volume of the surrounding water     

Delignification of cell walls of <Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis> during alkaline nitrobenzene oxidation

To clarify the behavior of whole lignins in wood cell walls during alkaline nitrobenzene oxidation, the delignification process from cell walls in normal and compression woods of Chamaecyparis obtusa Endl. (Cupressaceae) was observed using ultraviolet and transmission electron microscopies. The lignin content conspicuously decreased to around 10% after 35min in normal wood. The lignin content in compression wood finally leveled off at aroumd 10% after 50min. In gel filtration of oxidation products in ethyl acetate, a high molecular weight fraction was prominent in extracts from the early stage of the reaction. As the oxidation progressed, the high molecular weight fraction became less prominent in both normal and compression wood. Changes in the weights of cell wall residues during reaction indicated that approximately half of the components other than lignin were also removed from the cell walls. This shows that the majority of lignin with relatively high molecular weight is removed from the cell walls together with polysaccharides in the early stage of the reaction and that further oxidative degradation occurs in solution in later stages. Only a small amount of the lignin with low molecular weight could be analyzed by gas chromatography.Parts of this report were presented at the 47th (Kochi, April 1997) and 48th (Shizuoka, April 1998) Annual Meetings of the Japan Wood Research Society, and at the Lignin Symposium, Sapporo, October 1997     

Effect of impregnation on mechanosorption in wood and paper studied by dynamic mechanical analysis

The results of dynamic mechanical measurements in dual cantilever and uniaxial tension of untreated Scots pine veneer and unbleached sulphate paper under stepwise changes in the relative humidity of the surrounding atmosphere between 5% and 85% are compared to corresponding results for acetylated samples and samples treated by impregnation with poly(ethylene oxide) (PEO), glycerol or melamine formaldehyde resin. The treatments resulted in significant reductions in the transient mechanical losses associated with stepwise humidity changes. Although acetylation of wood and impregnation with PEO or glycerol both result in greatly improved dimensional stability with respect to humidity changes, the two types of treatment appear to be fundamentally different in terms of the models used here to interpret the results.We find that it is helpful to consider the dynamic process of moisture sorption/ desorption in these samples in terms of two coupled processes: the diffusion of moisture into or out of the sample, with a characteristic diffusion time given approximately by t^* = /16)h²/D where h is the sample thickness and D a characteristic diffusion constant for the moisture in the material, and the attachment/detachment of (clusters of) water molecules to binding sites in the samples, apparently with characteristic chemical relaxation times of the order of seconds or minutes. Clearly, when the sample thickness is quite small, 0.8 mm in our case, and the diffusion coefficient of the order of 50 × 10^–8 cm²/s, then the characteristic diffusion time is about 40 minutes, already for these small dimensions more than an order of magnitude larger than the characteristic chemical relaxation time. By varying the frequency of the dynamic mechanical measurements these characteristic processes for untreated and treated samples can be probed in some detail.     

Manufacture and mechanical properties of binderless boards from kenaf core

Binderless boards were prepared from finely ground powders of kenaf (Hibiscus cannabinus L.) core under varying manufacturing conditions. This research was designed to investigate their mechanical properties and evaluate the various manufacturing conditions: pressing temperature and time, pressing pressure, board density, board thickness, grain size of raw materials, and addition of furfural. The mechanical properties (i.e., modulus of rupture and elasticity, internal bonding strength) of boards increased with increasing board density and met the requirement for 15 type medium-density fiberboard (MDF) by JIS A 5905-1994. Thickness swelling and water absorption of boards exceeded the maximum permitted levels for 15 type MDF and S20 grade hardboard by JIS A 5905-1994, which indicates the low water-resistant property of binderless boards. In contrast to that in usual wood-based materials, internal bonding strength showed significant correlations with other board properties: modulus of rupture and elasticity, thickness swelling, and water absorption. We confirmed experimentally that the best manufacturing conditions proved to be as follows: pressing temperature 180°C, time 10min; pressing pressure 5.3MPa; board thickness 5mm; board density 1.0g/cm³; average grain size 53µm; and powder with no furfural content.Part of this paper was presented at the 52nd Annual Meeting of the Japan Wood Research Society, Gifu, April 2002     

Bearing properties of engineered wood products I: effects of dowel diameter and loading direction

The embedment tests of laminated veneer lumber (LVL) with two moduli of elasticity (MOE; 7.8 GPa and 9.8GPa), parallel strand lumber (PSL), and laminated strand lumber (LSL) were conducted in accordance with ASTM-D 5764. The load-embedment relation for each of these engineered wood products (EWPs) was established. The directional characteristics of bearing strength (_e), initial stiffness (k _e), and effective elastic foundation depth were obtained from the tested results. The effective elastic foundation depth (=E/k _e,E = MOE), based on the theory of a beam on elastic foundation, was obtained from thek _e and MOE. An of 90° (perpendicular to the grain) was calculated by dividingE ₉₀ [MOE of 90° from the compression test, but MOE of 0° (E ₀), parallel to the grain, obtained from the bending test] byk _e90, the initial stiffness of 90°. This study aimed to obtain the bearing characteristics of each EWP, taking into consideration their anisotropic structures, for estimating the fastening strength of a dowel-type fastener. The relations between the bearing coefficients ( _e,k _e,) on the loading direction and dowel diameter were established from the load-embedment curves. Based on the results of the embedment test, tested EWPs showed different tendencies in all directions from wood and glued laminated timber.Part of this study was presented at the 49th Annual Meeting of the Japan Wood Research Society, Tokyo, April 1999     

Study of the release in water of a chemical used for preservation of wood. Effect of the dimensions of the wood

Summary Various chemicals are used for protecting wood samples against fungi, and some of them are released in water, leading to pollution of the water. The kinetics of release of pentachlorophenol in water has here been studied, by considering the diffusion through the wood along the three principal axes of diffusion. The experiments and the modelling of the process is successfully coupled. The numerical model takes the three principal diffusivities, the partition factor, the volumes of wood and water into account. The effect of the length of the wood sample taken along the longitudinal axis of diffusion is especially studied, as the longitudinal diffusivity is much higher than the other two principal diffusivities. The effect of the relative volumes of wood and water is also of considerable interest not only for the concentration of the chemical in water but also for the rate of release.Symbols C concentration of liquid (g/cm³) - C_s, C_eq,t concentration of liquid on the surface, at equilibrium with the surrounding, respectively - C_i,j,k concentration of liquid in the wood at position (i, j, k) - D diffusivity (cm²/s) - h coefficient of mass transfer on the surface (cm/s) - i, j, k integers characterizing the position in the wood - K partition factor - L, R, T dimensions of the parallelepipedic wood sample - Mini amount of chemical contained in the wood at the beginning of the desorption - M_L, M_R, M_T dimensionless numbers - M_t, M amount of chemical released up to time t, up to infinite time, respectively - N half-number of slices taken in the wood parallelepiped along each dimension - V_water volume of the surrounding water - x, y, z coordinates - L, R, T thickness of the slices taken in the wood for calculation - t increment of time     

Veneer grades, recoveries, and values from 5-year-old eucalypt clones

Context

Processing young, small eucalypt logs into veneer is a burgeoning industry across southern China. However, plantations supplying these logs were mostly established for pulpwood; little information is available on variation and selection among commercial eucalypt clones/varieties in regards to suitability for veneer production.

Methods

Tree growth and log form were assessed on 11 eucalypt clones from a 5-year-old trial in southern China. Logs from these were rotary peeled for veneer; recovery percentages plus a range of quality and value traits were assessed on the outturn.

Results

Tree volumes, green veneer recovery ratios (%), veneer quality grades, log value, and value m^?3 varied significantly among both clones and log positions up the stem. The clone with the best veneer recovery ratio (50.5 %) provided nearly twice that of the poorest clone (28.4 %). Average veneer value log^?1 by clone ranged from RMB 6.7 (US$1) up to RMB 15.1 (US$2) and average value m^?3 by clone ranged from 589 RMB?m^?3 (US$88) up to 925 RMB?m^?3 (US$139). Overall, sweep was the key factor influencing veneer recovery ratio and value. Knots, especially dead knots, holes and splitting were major factors influencing veneer quality grade. Middle and upper logs had significantly higher veneer recoveries, grades, and values m^?3 than the lower logs.

Conclusions

Excellent potential exists for selecting among eucalypt clones, and even among log positions within trees, for optimizing veneer production.     

Assessment of hygroscopic conditioning performance of interior decorative materials IV: Sorption characteristics of wood under high relative humidity condition

The equilibrium moisture content (EMC) of six wood species under desorption conditions of 20°C and 100% 0% relative humidity (RH), and the rate of adsorption at various depths of three wood species blocks under 98% RH at 22.5°C were studied. There were no significant differences among the EMC values for these six wood species over the RH range 40% 0%, but there were highly significant differences over the RH range 100% 50% at constant 20°C. The amount of moisture absorbed in the wood decreased curvilinearly with the increase of depth in the specimens as sorption time increased, and their relation could be represented by a semilogarithmic equation. Time-dependent adsorption behavior at various depths of the wood specimens could be represented by an exponential equation as a function of the product of the difference between moisture contents at equilibrium and initial conditions and the term (1 – e^–t/). The value of of various wood species was found to increase linearly with the increased depth of the specimen and showed the following trend: hard maple (Acer sp.) > China fir (Cunninghamia lanceolata) > Japanese cedar (Cryptomeria japonica D. Don).Part of this report was presented at the 47th annual meeting of the Japan Wood Research Society, Kochi, April 1997.     

Methods to estimate the length effect on tensile strength parallel to the grain in Japanese larch

To find a desirable method for estimating the length effect on tensile strength ( _t), we used three methods to analyze the _t data from a Japanese larch (Larix kaempferi) small, clear specimen. These methods included a nonparametric method, the projection method of Hayashi, and a proposed method. The estimated length effect parameters (g) by the nonparametric method were 0.0237 and 0.0626 for 50th and 5th percentile _t distributions, respectively. The projection method requires a standardE _f level (E ^*: dynamic Young's modulus), arbitrarily chosen for calculating theg value. Theg values from the projection method were 0.1122 for lowE ^*, 0.0898 for averageE ^*, and 0.0759 for highE ^*. The estimatedg values by the proposed method using selected _t data were 0.1020 and 0.1838 for the 50th and 5th percentiles, respectively. Among the three methods, the nonparametric method did not consider the different distribution of Young's modulus among specimens, and the estimated length effect parameters (g) by this method were small. The projection method reduced the influence of Young's modulus, but the length effect parameters varied with theE ^* level. The proposed method minimized the dependence onE _f distributions among specimens. we believe the latter method is desirable for estimating the length effect on tensile strength.     

Working mechanism of adsorbed water on the vibrational properties of wood impregnated with extractives of pernambuco (Guilandina echinata Spreng.)

To clarify the lowering mechanism of loss tangen (tan) of sitka spruce (Picea sitchensis Carr.) wood impregnated with extractives of pernambuco (Guilandina echinata Spreng. synCaesalpinia echinata Lam.), we examined the vibrational properties of the impregnated wood in relation to the adsorbed water. The results obtained were as follows: (1) The equilibrium moisture content (EMC) of impregnated sitka spruce decreased to some extent compared with untreated wood. (2) Frequency dependencies of tan a about 400–8000Hz showed that impregnated wood has much lower tan than untreated wood at around 9% mois ture content (MC), except for the high-frequency region. At high relative humidity, impregnated wood has a minimum tan (at around 4000Hz); and at other frequency ranges the tan of impregnated wood did not differ considerably from that of untreated wood. (3) The apparent activation energy of the mechanical relaxation process (E) concerned with adsorbed water molecules was higher for impregnated specimens than for untreated ones at moderately high relative humidity, whereas at high relative humidity the difference was not observed. Based on these results, it is thought that the tan of impregnated wood decreased at low rela tive humidity because of the formation of direct hydrogen bonds between impregnated extractives and wood components. However, when the specimen is at higher relativePart of this work was presented at the 48th annual meeting of the Japan Wood Research Society, Shizuoka, April 1998 humidity, the formation of direct hydrogen bonds are disturbed by the existence of a large number of water molecules, and some extractives act as a plasticizer.     

On the activation energy of diffusion of water in wood

Summary The diffusion equation for water in wood is expanded in terms of temperature and moisture gradient on the assumption that the driving force for the diffusion of water in wood is the partial pressure of water vapour. An analytic expression is then developed for the activation energy of diffusion in terms of enthalpy and entropy changes associated with the sorption process. The expression is compared with another published curve and some similarity was observed.Symbols C water concentration, kg/m³ - D diffusion coefficient for water vapour in wood with vapour pressure as the driving potential, kg/ms Pa - D_c diffusion coefficient for water vapour in wood with water concentration as the driving potential, m²/s - D_c a constant value of D_c, m²/s - E activation energy of diffusion, J/kg - F flow density, kg/m² s - f h/l - h specific enthalpy, J/kg - L l/R T - l latent heat of vapourization of free water, J/kg - l_s latent heat of vapourization of sorbed water, J/kg - p partial pressure of water vapour, Pa - p_s pressure of water vapour at saturation, Pa - R specifc gas constant for water, J/kg K - r relative humidity - s specific entropy, J/kg K - w dry basis moisture content - x length coordinate, m - a constant temperature equal to 6,800 K - -/ln r - _w density of wood (dry mass/moisture volume) at a given moisture content, kg/m³ - s/R - L style as 2 lines above - free water relative to sorbed water The author is grateful to the Editorial Board in relation to the use of (4)     

Characterization of cellulose in compression and opposite woods of a Pinus densiflora tree grown under the influence of strong wind

Summary Structural factors in a Pinus densiflora tree grown under the influence of strong wind were measured. No difference for cellulose molecules was noticed between compression and opposite wood, but the was somewhat lower in the region where the compression wood was concentrated. The degree of crystallinity of cellulose was 45–50% in compression wood, about 50% in normal wood, and 50–60% in opposite wood. The crystallinity decreased with increasing height above the ground. The maximum point of crystallographic b-axis (fiber axis) orientation distribution for cellulose crystallites in compression wood was located at 30°, in normal wood at 25° and in opposite wood at 0°. The cellulose crystallite dimension in the transverse direction was 3.2 nm, corresponding to four cellulose unit cells, a value that was almost constant throughout the wood. In the longitudinal direction, there were large differences in cellulose crystallite dimensions between compression and opposite woods. In compression wood the cellulose crystallite dimensions was 12 nm corresponding to 11–12 cellulose unit cells. In opposite wood it was 17–32.5 nm corresponding to 17–32 cellulose unit cells. These structural factors were apparently affected by the environmental conditions, and the mechanical properties of the wood were influenced by these factors. Opposite wood had longer crystallites, a higher degree of crystallinity and a better orientation distribution of cellulose crystallites in the longitudinal direction. Compression wood, on the other hand, had shorter crystallites, a lower degree of crystallinity and a large angle between the stem and the direction of the crystallites.     

Plastic deformation in small clear pieces of Scots pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis>) during densification with the CaLignum process

Specimens made of clear wood from Scots pine (Pinus sylvestris L.) were compressed semi-isostatically at 25°C in a Quintus press. Pressure ranged from 0 to 140MPa and the maximum decrease in the crosscut area was about 60%. Quarter-sawn and plain-sawn specimens were densified with the inside face (pith side) up or down. A laser-made dot grid on the crosscut area of the uncompressed specimen was used to calculate plastic strains by image analysis of the displacement of dots after compression. Multivariate models were developed to determine the causes of deformation. The lower face was restrained by the press table and remained flat whereas sides attached to the rubber diaphragm became more irregularly shaped when compressed. Most of the total compression occurred below 50MPa and was determined exclusively by pressure. Above 50MPa, wood density was more important and compression was lower in the interior of specimens and in heartwood. Plastic compressive strain occurred predominately in the radial direction and toward the rigid press table. Strains were dependent on the sawing pattern and orientation. The growth rings of quarter-sawn specimens oriented with the outer face (bark side) down tended to buckle.     

Estimation of evaporation rate from the forest floor using oxygen-18 and deuterium compositions of throughfall and stream water during a non-storm runoff period

Rainwater, throughfall, stream water during a non-storm runoff period, and soil water were sampled about every 10 days at six nested basins within the Hitachi Ohta Experimental Watershed in Japan from 1998 to 2001. Basins HA and HB are covered with an 80-year-old artificial forest of Japanese cypress and Japanese cedar. HC and HV are covered with 12-year-old forest of the same species. HO and HX are covered with various aged stands of the same species. The samples were analyzed for the isotopic compositions of ¹⁸O and deuterium (D). The weighted means of ¹⁸O (D) in HA and HB were –7.35 (–46.7) and –7.38 (–46.8), while they were –7.51 (–48.1) and –7.57 (n/a) in HC and HV, respectively. They were –7.50 (–47.6) and –7.41 (–47.1) in HO and HX, respectively. There was a relative difference of 0.2 (1.4) in ¹⁸O (D) between 80-year-old and 12-year-old forest. The stream water during a non-storm runoff period is considered to reflect the effect of evaporation from the forest floor. The evaporation rates from the forest floor were estimated using values in throughfall and stream water using the Rayleigh distillation equation under equilibrium conditions. They were estimated to be 5.5 (9.1), 5.2 (9.0), and 4.9 (8.7)% of annual throughfall in HA, HB, and HX (mature forests), respectively, using ¹⁸O (D), and 4.0 (7.6), 4.1 (8.1), and 3.5 (n/a)% of annual throughfall in HC, HO, and HV (young forests), respectively.     

The lamination influence on properties of agro-based particleboard

Abstract

Response surface methodology (RSM) based on a three-level, three-variable central composite rotatable design was applied to evaluate the effects of the parameters such as ratio of rice straw (Oryza sativa)/poplar (Populus deltoids) wood particle bonded with urea-formaldehyde resin in panels, species of wood veneer coating these panels and amount of adhesive in glue line on the modulus of rupture (MOR), internal bonding (IB), and thickness swelling (TS) of panels. Mathematical model equations were derived by computer simulation programming to optimize the properties of the particleboard. These equations that are second-order response functions representing MOR, IB, and TS were expressed as functions of three operating parameters of panel properties. Predicted values were found to be in a good agreement with experimental values (R ² values of 0.96, 0.98 and 0.98 for MOR, IB, and TS, respectively). This study has shown that the RSM could efficiently be applied for modeling panel properties. It was found that the variables affected the properties of panels. Straw usage up to 30% in the mixture did not cause a significant decrease in MOR, IB, and TS. Using beech veneer and 190 g/m² glue line had the highest MOR and lowest TS.     

Structure of xylan from culms of bamboo grass (Sasa senanensis Rehd.)

Xylan prepared from culms of kumaizasa (Sasa senanensis Rehd.), a representative species of bamboo grass, was hydrolyzed with-xylanase ofStreptomyces olivaceoviridis E-86. Four arabinoxylo-oligosaccharides and two glucuronoxylo-oligosaccharides were isolated from the enzymatic hydrolysate of the xylan by chromatography on a charcoal column, a Dowex 1-x8 column, a Toyo-pearl HW-40S column, and a LiChrospher 100 NH₂ column and on preparative paper chromatography. The results of the structural analyses of the saccharides showed that the isolated oligosaccharides had the structures of 3²--l-arabinofuranosyl-xylobiose, 3²--l-arabinofuranosyl-xylotriose, 3²--[-d-xylopyranosyl-(1 2)-l-arabinofuranosyl]-xylobiose, 3³--[-d-xylopyranosyl-(1 2)-l-arabinofuranosyl]-xylotriose, 2³--4-O-methyl-d-glucuronosyl-xylotriose, and 2³--d-glucuronosyl-xylotriose. From the structural analysis of the oligosaccharides derived from the xylan, kumaizasa xylan was concluded to be a kind of arabinoglucuronoxylan having not only stubs of singlel-arabinose and singled-glucuronic acid but also stubs of disaccharide units such as-d-xylopyranosyl-(1 2)-l-arabinofuranose.     

Simultaneous drying and densification of silver birch (Betula pendula L.) veneers: analysis of morphology,thickness swelling,and density profile

In this study, birch (Betula pendula L.) veneers were simultaneously densified and dried using a contact drying method at pressures of 1.5 and 3 MPa at 130 °C and compared with veneer dried in a laboratory-scale convective type dryer. Compression rate, thickness swelling, and the density profiles of the veneers were investigated. Furthermore, the microstructure of densified veneers was studied by scanning electron microscopy (SEM). A maximum veneer compression rate of 9 % was achieved at a pressure of 3 MPa. Under these conditions, the veneers were, on average, densified from 504 to 574 kg m^?3 (approximately 14 %). After water soaking, full set-recovery—recovery to the initial thickness—occurred. However, the swelling rate was lower for the densified veneer. Density profiles measurements showed that densification occurs throughout the veneers. The SEM images showed that the surface of the densified veneers were smoother, whilst no cracks were detected due to densification. Densification seemed to occur in vessels. Typically, rays were bent when there was a vessel nearby.     

Veneer strand flanged I-beam with medium density fiberboard or particleboard as web material I: the forming method and fundamental properties

I-beams flanged with veneer strands with medium density fiberboard (MDF) or particleboard as web material were produced by hot pressing. The forming and pressing method used a special metallic mould that allowed flanges to be formed and bonded to the web at the same time. Many I-beams were able to be produced in a single hot pressing cycle and this method allows the utilization of residues and wastes from wood and wood-composite industries. The forming and pressing method was found to be technically suitable for the production of such I-beams. The fundamental properties of the specimens produced were assessed and the results indicated that the I-beams had promising mechanical properties; for example, the modulus of rupture ranged from 40 to 56MPa depending on the flange density. The bond quality between the web and flange was found to have a critical effect on the strength of the entire I-beam. The I-beams were found to have relatively high bond strengths between the web and flange, ranging from 3.3 to 5.0MPa in the parallel direction. The dimensional stability of the I-beams was found to be excellent in the thickness direction of the beam, but not in the compression (width) direction.Part of this paper was presented at the 53rd Annual Meeting of the Japan Wood Research Society in Fukuoka, March 2003     

Postbuckling of thin wood-based sandwich panels due to hygroexpansion under high humidity

This study was carried out to investigate the postbuckling behavior of thin wood-based sandwich panels under high humidity. Using the Rayleigh-Ritz method based on the von Karman nonlinear theory for the panel, the solutions for both the approximate and the closed form for postbuckling of orthotropic panels were derived to evaluate the deflection for the boundary condition of all clamped edges. The results suggested that the edge movement be considered for evaluation of a critical moisture content and deflection of thin wood-based panels fixed on the core with an adhesive. The numerical solution obtained from the derived model showed some discrepancy with the experimental results. The predicted results overestimated the center deflection of the panels because creep and plastic deformation might be caused by considerable in-plane stress on panels.Appendix: Abbreviations and symbols total potential energy of panel - A _ij ,D _ij extensional and bending stiffness, respectively - _x , _y midplane strains inx andy directions, respectively - _xy midplane shear strain inxy plane - N _x ^M , N _y ^M hygroscopic forces inx andy directions, respectively - h panel thickness - a, b panel length inx andy directions, respectively - x, y, z coordinate system - u, v, w displacement inx, y, andz directions, respectively - MC moisture content change - a _x ,a _y coefficient of linear expansion inx andy directions, respectively - LE linear expansion (MC) - s arc length - R radius of curvature - N _x ,N _y resultant in-plane forces per unit length inx andy directions, respectively - N _n nondimensional loadN _x ^M b ²/E ₂ h ³ - N _cr nondimensional critical load,N _x,cr ^M b ²/E ₂ h ³ - ratio of the core to the total width,a _c /a + a _c - E _c effective core MOE,E +E (i.e., the summation of MOE parallel to the grain and perpendicular to the grain) - h _c core thickness