Elastic moduli and stiffness optimization in four-point bending of wood-based sandwich panel for use as structural insulated walls and floors

Several wood-based sandwich panels with low-density fiberboard core were developed for structural insulated walls and floors, with different face material, panel thickness, and core density. The elastic moduli with and without shear effect (E _L, E ₀) and shear modulus (G_b) were evaluated in four-point bending. Generally, the stiffer face, thicker panel, and higher core density were advantageous in flexural and shear rigidity for structural use, but the weight control was critical for insulation. Therefore, optimum designs of some virtual sandwich structures were analyzed for bending stiffness in relation to weight for fixed core densities, considering the manufactured-panel designs. As a result, the plywood-faced sandwich panel with a panel thickness of 95 mm (PSW-T100), with insulation performance that had been previously confirmed, was most advantageous at a panel density of 430 kg/m³, showing the highest flexural rigidity (E _L I = 13 × 10⁻⁶ GNm²) among these panels, where E _L, E ₀, and G _b were 3.5, 5.5, and 0.038 GN/m², respectively. The panel was found to be closest to the optimum design, which meant that its core and face thickness were optimum for stiffness with minimum density. The panel also provided enough internal bond strength and an excellent dimensional stability. The panel was the most feasible for structural insulation use with the weight-saving structure.     

Sandwich panel of veneer-overlaid low-density fiberboard

Low-density sandwich panels of veneer-overlaid fiberboards of 12 mm thickness for structural use were manufactured at densities of 0.3–0.5g/cm³ using an isocyanate compound resin adhesive and steam injection pressing method. The effects of board density, veneer thickness, and resin content on the fundamental properties of sandwich panels were examined, with the following results: (1) The dry moduli of rupture and elasticity in the parallel direction of sandwich panels with thicker veneers were superior. The dry moduli of rupture and elasticity in the parallel direction of sandwich panels with 2.0 mm thick veneer at densities of 0.4–0.5 g/cm³ were 40–60 MPa, and 5–8 GPa, which were two and four times as much as those of homogeneous fiberboards, respectively. (2) The higher-density panels exhibited tensile failure at the bottom veneer surface during static dry bending in a parallel direction, whereas lower-density panels experienced horizontal shear failure in the core. (3) The dimensional stability of sandwich panels had good dimensional stability, with negligible springback after accelerated weathering conditions. (4) The thermal insulation properties of sandwich panels were found to be much superior to other commercial structural wood composite panels.Part of this report was presented at the 47th annual meeting of the Japan Wood Research Society, Kouchi, April 1997     

Characterization of wood-based molding bonded with citric acid

The wood-based moldings were fabricated by using only citric acid as an adhesive. The mechanical properties, water resistances, thermal properties and chemical structure were investigated. Wood powder obtained from Acacia mangium was mixed with citric acid under certain weight ratios (0–40 wt%), and each powder mixture was molded using two types of metal molds at 200°C and 4 MPa for 10 min. The modulus of rupture and the modulus of elasticity values of the wood-based molding containing 20 wt% citric acid were 35.8 MPa and 5.4 GPa, respectively. The maximum impact strength was 0.94 kJ/m² with the same citric acid content. The water resistance increased with increasing citric acid content, and the good resistance to boiling water was also recognized. However, some elution of substances derived from citric acid was observed at high levels of citric acid, causing a decrease in the thermal properties. The ester linkages were detected by Fourier transform infrared spectroscopy, indicating that the citric acid reacted with the wood. Our results demonstrated that citric acid brought about good adhesiveness for fabricating the wood-based molding.     

Supplementing pine with European beech and poplar in oriented strand boards

Abstract

The objective of the study was to compare the properties of oriented strand boards (OSBs) made from the following mixtures: European beech and poplar, beech and pine, poplar and pine and 100% pine (i.e. the conventional raw material for OSB in Europe). Panels with 50–50% of beech-poplar/beech-pine/poplar-pine at two density levels of 650 kg/m³ and 720 kg/m³ were made with 5% pMDI (poly methylene di-isocyanate) as binder at 180°C and 240s as press conditions. Results showed that panels comprising a mixture of European beech and poplar have higher mechanical properties compared to panels made with mixtures of pine-beech or pine-poplar. In addition, for all panels, when density is increased from 650 kg/m³ to 720 kg/m³, mechanical properties increased. Internal bond values for all designs were in the same range, especially at higher density (720 kg/m³). The pure pine panels showed lower values between different designs. Thickness swelling, an important physical property of OSB, improved when face and core layers consisted of a mixture of beech and poplar strands.     

In-plane shear properties of the wood-based sandwich panel as a small shear wall evaluated by the shear test method using tie-rods

 The fundamental in-plane shear properties were investigated for the wood-based sandwich panel of plywood-overlaid low-density fiberboard (SW) manufactured at a pilot scale to develop it as a shear wall. The shear test method using tie-rods standardized for shear walls was applied to SW with dimensions of 260 mm square and 96 mm thick as a small shear wall and to plywood (PW) and thick low-density fiberboard (FB). The shear modulus and shear strength of PW, FB, and SW were determined. To measure the shear deformation angle, a displacement meter and strain-gauge were used. The shear moduli of PW (0.68 g/cm³) and FB (0.25–0.35 g/cm³) were 460 and 21–58 MPa/rad, respectively. The shear modulus of SW as a composite was analyzed. Some experimental models of SW were proposed (i.e., rigid-α, rigid-β, flexible, and semirigid models). The shear modulus of SW (0.35–0.40 g/cm³) evaluated based on the rigid-α and semirigid models were 73–89 and 109–125 MPa/rad, respectively. The theoretical shear modulus of SW was calculated to be 110–129 MPa/rad. Received: May 9, 2001 / Accepted: June 26, 2002 RID="*" ID="*" Part of this report was presented at the 50th Annual Meeting of the Japan Wood Research Society, Kyoto, Japan, April 2000; and the 5th Pacific Rim Bio-Based Composite Symposium, Canberra, Australia, December 2000 Acknowledgments The authors express our deep gratitude to Mr. Noritoshi Sawada (Hokushin Co.), Dr. Wong Cheng, and their cooperative members for their expert technical support for the preparation of manufacturing the thick fiberboard and sandwich panel. We are grateful also to Drs. Min Zhang, Kenji Umemura, Wong Ee Ding, and Guangping Han for their great help and advice in manufacturing the thick panels. The authors are grateful to Hokushin Co. for the fiber and resin and to Ishinomaki Gouhan Co. for the plywood. We thank Mr. Makoto Nakatani for his expert assistance when preparing the specimens for the shear test. Funding provided by the Research Fellowship of the Japan Society for the Promotion of Science for Young Scientists as a JSPS Research Fellow is also gratefully acknowledged.     

Assessment of temperature and relative humidity conditioning performances of interior decoration materials in the Taipei area (II)

The purpose of this study was to explore the conditioning effects of wood panels (used as interior decorating materials). We examined hourly the temperature and relative humidity (RH) in a living environment based on the average values during winters from 1974 to 1990 in the Taipei area. Thirty-six interior finish materials attached to one inside surface of a 35cm³ simulation aluminum container were used in this study. An A/V value (surface area of interior decoration materials attached to container/inside volume of container) of 2.86m^–1 or various other A/V values and panel thicknesses had no significant effect on the room temperature changing ratio. The hygroscopic conditioning performances of these decorative materials were classified into four types in accordance withb values: type I (b>0.0200) included four solid woods (unfinished), two wood-based materials, three composite materials, and one inorganic material. Type II (0.0170<b<0.0199) included one solid wood, eight wood-based materials, and two inorganic materials. Type III (0.0070<b<0.0169) included 11 wood-based materials and four inorganic materials. The RH changing ratio decreased curvilinearly with increasing interior decorating panel thickness and A/V values in a sealed container, whereasb values increased with increasing interior decorating panel thickness and A/V values in a sealed container.Part of this report was presented at ICEUPT'99, Chi-Tou, Taiwan, ROC, May 21–23, 1999     

Assessment of temperature and relative humidity conditioning performances of interior decoration materials

The purpose of this study was to explore conditioning effects on wood panels (used as interior decorative materials). We examined hourly the temperature and relative humidity (RH) in a living environment based on the data of average values from 1974 to 1990 in the Taipei area. Thirty-six interior finish materials attached to one inside surface of a 35³ cu cm simulation aluminum container were used in this study. An A/V ratio (surface area/volume) of 2.86 (m^–1) or various other values and the panel thickness had no significant effect on the room temperature changing ratio. The hygroscopic conditioning performances of these decorative materials were classified into four types in accordance with b values: type I (b > 0.0200) included four solid woods (unfinished), seven wood-based materials, three composite materials, and one inorganic material. Type II (0.0170 <b < 0.0199) included one solid wood, five wood-based materials, and two inorganic materials. Type III (0.0070 <b < 0.0169) included nine wood-based materials, and four inorganic materials. The RH changing ratio decreased curvilinearly with increasing interior decorative panel thickness and A/V values in a sealed container, whereas theb values increased with increasing interior decorative panel thickness and A/V values in a sealed container.Part of this report was presented at IUFRO All Division 5 Conference, Washington State University, Pullman, WA, USA, July 7–12, 1997     

Feasibility of supercritical carbon dioxide as a carrier solvent for preservative treatment of wood-based composites

 Supercritical carbon dioxide (SC-CO₂) was tested for its potential as a carrier solvent for preservative treatment of solid wood and wood-based composites. A preliminary trial showed that the treatability of solid wood varied with its original permeability and that the SC-CO₂ treatment was not promising for refractory timber species such a Larix leptolepis Gordon. In contrast, 3-iodo-2-propynyl butylcarbamate (IPBC)/SC-CO₂ treatment resulted in enhanced decay resistance without any detrimental physical or cosmetic damage in all structural-use wood-based composites tested: medium density fiberboard, hardwood plywood, softwood plywood, particleboard, and oriented strand board (OSB). Further trials under various treatment conditions [25°C/7.85 MPa (80 kgf/cm²), 35°C/7.85 MPa, 45°C/7.85 MPa, 35°C/11.77 MPa (120 kgf/cm²), and 45°C/11.77 MPa] indicated that although small changes in the weight and thickness of the treated materials were noted the strength properties were not adversely affected, except for a few cases of softwood plywood and oriented strand board. The results of this study clearly indicated that the treatment condition allowed SC-CO₂ to transport IPBC into wood-based composites, and the optimum treatment condition seemed to vary with the type of wood-based composite. Received: October 24, 2001 / Accepted: February 15, 2002 Part of this work was presented at the 51st Annual Meeting of the Japan Wood Research Society, Tokyo, April 2001; and the 32nd Annual Meeting of the International Research Group on Wood Preservation, Nara, May 2001 Correspondence to:M. Muin     

Manufacture and properties of ultra-low-density fiberboard

Low-density fiberboards with densities ranging from 0.05 to 0.50g/cm³ were manufactured with steam injection pressing. Bond-type and foam-type isocyanate compound resin adhesives were used separately at 10% and 30% resin content levels. Two types of different-size fibers from softwood were used. Mechanical, dimensional, thermal, and sound insulation properties of the fiberboards were tested. The results are as follows: (1) Bond-type isocyanate adhesive showed higher mechanical and dimensional properties of low-density fiberboards than the foam-type adhesive. (2) Fiberboards produced from small fibers have better mechanical and dimensional properties than those made from large fibers. (3) Thermal conductivity of fiberboards depends more on the board density than on the type of resin or fiber dimension. At a board density lower than 0.2 g/cm³, the thermal conductivity is almost equivalent to those of thermal insulation materials such as polystyrene foam and rock wool, (4) Generally, the sound absorption coefficient of low-density fiberboards tends to increase at higher sound frequency. As the board thickness increases, low-frequency sounds are more readily absorbed by boards.Part of this report was presented at the 46th annual meeting of the Japan Wood Research Society, Kumamoto, April 1996     

Thermal properties of interior decorative material and contacted sensory cold-warmth I: relation between skin temperature and contacted sensory cold-warmth

The purpose of the study was to investigate the relation between the skin temperature of the palm and sensory cold-warmth after contact with some materials. Ten men and ten women were selected and introduced to 21 kinds of material for a contact test of 30 min without seeing the specimens in a climate-controlled room at 25±1C and 65% relative heemidity. The palm-contacted test materials and skin temperature of the palm, central fingertip, and back of the palm were measured during the experiment. A sensory evaluation test was applied to evaluate the contacted sensory cold-warmth. Results showed that the maximum temperature decrease of the fingertip (T _d) was positively related to the natural logarithm of the material's specific gravity (ln _u) and to the natural logarithm of the material's thermal conductivity (ln). There were also negative linear relations between the contacted sensory cold-warmth (S) with ln _u and ln; and there was a negative linear relation betweenS withT _d and betweenS with the value ofT _d by . The thermal osmotic coefficient (b) of wood and wood-based materials ranged from 3.63 to 3.97, and the materials were qualified as good thermal insulation materials. Furthermore, there was a negative linear relation betweenS andb. Accordingly, it is possible to evaluate the contacted sensory cold-warmth relying on the basic thermal properties of material.Part of this report was presented at the 49th Annual Meeting of the Japan Wood Research Society, Tokyo, April 2–4, 1999     

Difference in mass concentration of airborne dust during circular sawing of five wood-based materials

The object of this study was to compare the mass concentration of airborne dust during circular sawing of five wood-based materials: solid sugi (Cryptomeria japonica) lumber, tropical hardwood plywood, softwood plywood, particleboard, and medium-density fiberboard. Specimens were sawn at a constant feed per tooth (0.05 mm) using two saw speeds. The mass concentration of airborne dust of diameter 7.07 μm or less (respirable dust) was measured with a light-scattering dust monitor. The mass concentration showed a log-normal distribution, and the geometric means of mass concentration at saw speeds of 2000 and 3000 rpm were 2.33 and 2.89 mg/m³ for tropical hardwood plywood, 1.13 and 2.84 mg/m³ for particleboard, 0.91 and 2.28 mg/m³ for medium-density fiberboard, 1.09 and 1.38 mg/m³ for softwood plywood, and 0.32 and 0.66 mg/m³ for sugi lumber. The mass concentration for all five wood-based materials increased with the revolution speed of the circular saw.     

Shrinkage-related degrade and its association with some physical properties in Eucalyptus regnans F. Muell

Summary Assessments of internal checking and the physical properties of 124 trees of Eucalyptus regnans F. Muell. have shown that for material dried under relatively mild predryer conditions (30 °C, 65% RH) internal checking was highly positively correlated with each of collapse, moisture content and normal shrinkage, and weakly negatively correlated with total external shrinkage. Collapse alone explained 47% of the variation in internal checking. Incidence of internal checking in sample boards could be estimated with moderate success by each of the following properties measured on board ends: collapse, the number of internal checks and initial moisture content. Material with high mean basic density above 530 kg/m³ was associated with low levels of internal checking and collapse. However, the maximum naturally occurring density of E. regnans was not high enough to obviate collapse and internal checking. It was observed that growth rings in 100 × 50 mm backsawn boards in which the earlywood air-dry density was below 450 kg/m³ showed internal checking. The size and number of internal checks increased with a decrease in earlywood density. It was shown that drying E. regnans below temperatures of 24–30 °C does not eliminate collapse, thus raising doubt about the validity of a temperature threshold concept in that range. Received 17 September 1997     

Manufacture and properties of low-density binderless particleboard from kenaf core

Low-density binderless particleboards from kenaf core were successfully developed using steam injection pressing. The target board density ranged from 0.10 to 0.30g/cm³, the steam pressure used was 1.0MPa, and the steam treatment times were 7 and 10min. The mechanical properties, dimensional stability, and thermal and sound insulation performances of the boards were investigated. The results showed that the low-density kenaf binderless particleboards had good mechanical properties and dimensional stability relative to their low board densities. The board of 0.20g/cm³ density with a 10-min treatment time produced the following values: modulus of rupture 1.1MPa, modulus of elasticity 0.3GPa, internal bond strength 0.10MPa, thickness swelling in 24h water immersion 6.6%, and water absorption 355%. The thermal conductivity of the low-density kenaf binderless particleboards showed values similar to those of insulation material (i.e., rock wool), and the sound absorption coefficient was high. In addition, the boards are free from formaldehyde emission. Kenaf core appears to be a potential raw material for low-density binderless panels suitable for sound absorption and thermally resistant interior products.Part of this report was presented at the 52th Annual Meeting of the Japan Wood Research Society, Gifu, Japan, April 2002     

Fire resistance of thick wood-based boards

Thick wood-based boards are used as construction materials for walls and floors in Japan. In this study, fire resistance tests (ISO 834-1) and cone calorimeter tests (ISO 5660-1) were conducted for thick plywood, particleboard, and medium density fiberboard with sample thicknesses of about 28–30mm, and their suitabilities for quasi-fireproof or fire-preventive structures were evaluated. In the ISO 834-1 fire resistance test, the heat-shielding performance (insulation criterion) for walls was evaluated and the results showed that the larger the apparent density of a woodbased board, the higher its insulation performance. The insulation performance of thick wood-based boards in the fire resistance test could be forecast from the results of the cone calorimeter test, especially when the second peak of heat release rate appeared. In the cone calorimeter tests, the surface layer density of the plywood, particleboard, and medium density fiberboard was the dominant parameter for the time to ignition and initial heat release rate. These results indicate that thick wood-based board is a suitable fire-preventive construction material. Part of this study was presented at the Annual Meeting of the Architectural Institute of Japan, Hokkaido, Japan, August 2004     

Sensory irritations and pulmonary effects in human volunteers following short-term exposure to pinewood emissions

Pinewood (Pinus ssp.) is widely used for furniture and building purposes. However, despite its widespread use, information on possible human sensory irritations and pulmonary effects caused by exposure to volatile organic compounds (VOC) emitted from pinewood is sparse. For this purpose, (1) sensory irritation of eyes, nose and throat, (2) lung function parameters (FVC, FEV₁), (3) exhaled nitrogen oxide (NO) concentration, (4) eye blink frequency, and (5) sensory evaluation (using the SD method) were investigated before, after, and partly during exposure of human volunteers to emissions from pinewood panels. Fifteen healthy nonsmokers were exposed for 2 h under controlled conditions to VOCs emitted from pinewood panels in a 48 m³ test chamber. VOC concentrations were about 5 mg/ m³ (loading rate, 1 m²/m³), 8 mg/m³ (loading rate, 2 m²/m³), and 13 mg/m³ (loading rate, 3 m²/m³), respectively. Terpene and aldehyde exposure concentrations ranged from about 3.50 ± 0.51 mg/m³ and 0.07 ± 0.008 mg/m³, 5.00 ± 0.95 mg/ m³, and 0.20 ± 0.02 mg/m³ or 9.51 ± 1.10 mg/m³ and 0.21 ± 0.04 mg/m³ for loading rates of 1, 2, and 3 m²/m³, respectively. The emissions consisted predominantly of α-pinene and δ³-carene. No concentration-dependent effects before or after exposure to the emissions were measured with respect to sensory irritation, pulmonary function, exhaled NO, and eye blink frequency. Only the odor of the emissions was perceived by the study subjects, rated as being closer to “pleasant” than to “unpleasant.” In conclusion, the results of our study suggest that short-term exposure to high VOC concentrations, even up to 13 mg/m³, released from pinewood does not elicit sensory irritation or pulmonary effects in healthy humans under controlled conditions.     

Microscopic structure and properties of wood-based foaming composites

In order to reduce the density of wood-based composites without causing a deterioration of their mechanical properties, we studied the process of manufacturing wood-based composites. A combination of polymer foaming technology and flat hot-pressing technology was used. The microscopic structure of the various wood-based composites was analyzed with a scanning electron microscope (SEM). Modulus of rupture (MOR), modulus of elasticity (MOE), impact strength, and thickness expansion rate of water sorption (TS) were all measured. The results showed that fibers loosely interweave, and fibers had been connected by micropore. They also showed that spaces between fibers had big micropore structure. MOR, MOE and impact strength were the highest among three levels of ratio. When the total content of resin and foaming agent were 20% by weight, TS was higher. A hot-pressing temperature of 120°C was optimal. At the low temperatures of 80°C, the foaming process was uncompleted. At a higher temperature, micropores burst at a certain pressure. Based on the variance analysis and maximum difference analysis, a significance test shows that the optimum conditions for the total content of resin and foaming agent is 20% by weight, with a hot pressing temperature of 120°C for 15 min. Under these conditions, the properties of wood-based foaming composites all achieved the industry standard. __________ Translated from Journal of Beijing Forestry University, 2007, 29(3): 154–158 [译自: 北京林业大学学报]     

On the measurement of formaldehyde release from low-emission wood-based panels using the perforator method

In Europe, the perforator method (EN 120) is the mostly used laboratory method of the wood-based panel industry. Usually, the measured perforator value depends on the moisture content of the boards. According to DIBt-100, the measured perforator values are corrected to a common moisture content (MC) of 6.5% using an established equation proposed by Jann and Deppe (1990). The correction factor of Jann and Deppe (1990) is based on the assumption that particle- and fibreboards change their perforator values to the same extent regardless whether increasing or decreasing the moisture content in the range of 3 ≤ u ≤ 9%. Application of this correction factor to particle- and fibreboards of higher moisture content than 6.5% can lead to biased corrected results in favour of low emission. The corrected values can also lead to paradoxical relation between the perforator values and emission in the low-emission region.     

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.     

Chemical and physical changes required for producing dimensionally stable wood-based composites

Summary High temperature (240°C) contact treatment was shown to be a very effective method of stabilizing panels bonded with heat resistant adhesive. Chemical analyses of post treated boards indicate that chemical changes of the wood components due to contact heat treatment were negligible. The results support the concept that high temperature post treatment of boards at temperatures above the softening points of lignin and carbohydrate components, caused plastic flow in situ which relieved internal stresses built up during hot pressing. Consequently, springback in wood-based composites diminished leaving panels much more stable than conventional products. Also, dimensionally stable wood-based composites had a better inherent ability to withstand severe exposure conditions than the regular boards.The authors wish to thank G. Bastien and B. S. Lethbridge for technical assistance. One of the authors (W.S.) is grateful to the Fonds zur Förderung der wissenschaftlichen Forschung, Vienna, Austria for financial support (Proj. No. J0128C)     

Digital X-ray analysis of density distribution characteristics of wood-based panels

Twelve commercial nominal 4 × 8 ft.² (1,200 × 2,400 mm²) wood-based panels, Medium Density Fiberboard, Particleboard, Oriented Strand Board and Plywood, were scanned for horizontal density distribution using a high resolution and accuracy digital X-ray system. Density distribution at a size of grid cell varying from 0.5 × 0.5 to 12 × 12 in.² (12.7 × 12.7 to 304.8 × 304.8 mm²) was analyzed based on the X-ray scanned images of the panels. Detailed density distribution characteristics of the four types of wood-based panels are presented in this research. Comparisons of density variation are carried out between different panel types and between different spatial resolutions (i.e. sizes of grid cells). Results of analysis and comparison in density distribution are presented in different forms with industrial as well as academic implications.