Hidefumi Yamauchi

Bending characteristics of bamboo (Phyllostachys pubescens) with respect to its fiber–foam composite structure

The bending properties of split bamboo culm were compared with those of spruce and beech wood specimens. The bamboo allowed large flexural deformation since its outer layer retains the tensile stress while the softer inner layer undergoes large compressive deformation. The results suggested that the combination of the fiber-rich outer part and the compressible inner part was responsible for the flexural ductility of split bamboo. To clarify the compressible nature of the inner part of bamboo, the longitudinal surfaces of the bamboo and wood specimens were microscopically observed before and after a large longitudinal compression. Although the wood specimens showed serious and localized buckling, the inner part of the bamboo specimens showed no such visible buckling. In the latter case, the foam-like parenchyma cells absorbed the large compressive deformation by their microscopic buckling and simultaneously, the alignment of sclerenchyma fibers was maintained by the surrounding parenchyma matrix. The flexural elasticity of the bamboo was compared to that of the wood in respect of remaining strain during cyclic bending tests. No clear difference was recognized between their remaining strains. This fact indicated that the bamboo was not so flexible elastically, although its fiber–foam combination and intelligent fiber distribution improve flexural ductility.

Development of binderless fiberboard from kenaf core

Binderless fiberboards with densities of 0.3 and 0.5 g/cm3 were developed from kenaf core material using the conventional dry-manufacturing process. The effects of steam pressure (0.4–0.8 MPa) and cooking time (10–30 min) in the refining process, fiber moisture content (MC) (10%, 30%), and hot-pressing time (3–10 min) on the board properties were investigated. The results showed that kenaf core binderless fiberboards manufactured with high steam pressure and long cooking time during the refining process had high internal bond (IB) strength, low thickness swelling (TS), but low bending strength values. The binderless fiberboards made from 30% MC fibers showed better mechanical and dimensional properties than those from air-dried fibers. Hot-pressing time was found to have little effect on the IB value of the binderless board at the refining conditions of 0.8 MPa/20 min, but longer pressing time resulted in lower TS. At a density of 0.5 g/cm3, binderless fiberboard with the refining conditions of 0.8 MPa/20 min recorded a modulus of rupture (MOR) of 12 MPa, modulus of elasticity (MOE) of 1.7 GPa, IB of 0.43 MPa, and 12% TS under the optimum board manufacturing conditions.

Passive impregnation of liquid in impermeable lumber incised by laser

Square lumber specimens of laser-incised Douglas fir (Pseudotsuga menziesii Franco) were treated with steam before dipping. Two types of steam (saturated steam and superheated steam), three steam-injection times (5, 10, and 20 min), four different time intervals (moving time) between steam treatment and dipping (immediate, 3, 10, and 30 min), and four different dipping times (0.5, 1, 3, and 12 h) were used in the study. The maximum absorption was 480 kg/m3 when saturated steam was injected for 20 min and the specimen was immediately dipped into liquid for 12 h. Samples treated with this condition not only absorbed the maximum amount of liquid but also penetrated over 83.4% and 87.3% of the total area along and across the grain, respectively. The optimum conditions were then applied to laser-incised sugi (Cryptomeria japonica D. Don) and Japanese larch (Larix leptolepis Gordon) where the absorption of liquid was 415 and 187 kg/m3, respectively. It was shown that initial moisture content below the fiber saturation point was good for passive impregnation. The absorption of liquid and its distribution in wood indicates that it can be a good preservative treatment method for impermeable woods.

Design and pilot production of a “spiral-winder” for the manufacture of cylindrical laminated veneer lumber

A new spiral-winder was developed for continuous manufacturing of cylindrical laminated veneer lumber (LVL), and a suitable resin adhesive for this cylindrical LVL manufacturing system was investigated. This phase was followed by trial manufacturing and evaluation of cylindrical LVL with the optimum resin adhesive identified. The results are summarized as follows. (1) The shortest gelation time was recorded with a mixture of two commercial resorcinol based resins (DF-1000 and D-33) at a weight ratio of 25∶75. (2) Bath temperature had a remarkable effect on the gelation time of the adhesive mix. (3) High bonding strength was recorded by 25∶75 DF-1000/D-33 adhesive mix at a high press temperature despite a short pressing duration. Based on the results of items (1) to (3), 25∶75 DF-1000/ D-33 is recommended for use in the new spiral-winder. (4) The mechanical properties of cylindrical LVL could be improved by using 25∶75 DF-1000/D-33 with wider veneer width and longer pressing time. (5) The mechanical properties, especially the modulus of rupture, of the cylindrical LVL manufactured require further improvement for practical structural application.

Durability of isocyanate resin adhesives for wood V: changes of color and chemical structure in photodegradation

The effect of ultraviolet (UV) light irradiation on the color and chemical structure of water-cured polymeric diphenylmethane diisocyanate (PMDI) was investigated using a UV long-life fade meter. Control treatment was performed without UV light irradiation using a thermohygrostat for comparison. Two kinds of resin were used in this study: that to which only water had been added, and resin to which a small amount of polyol and water had been added. In addition, lauan (Shorea spp.) wood was used as a reference. The photodegradation of the resins over a period of up to 300 h was observed using a colorimeter and Fourier transform infrared (FT-IR) spectroscopy. When the resins were treated with UV light, the color difference (ΔE*ab) of the resins increased signifi cantly in a short time, and then reached a near-constant value. For lightness, L* decreased rapidly for a few hours and then decreased gradually. The color darkened compared with that of the wood used. When treatment was performed without UV light irradiation, ΔE*ab and ΔL* of the resins showed negligible change. Based on the results of FT-IR analysis, severe degradation such as cleavage of the main chemical bond was hardly observed under UV light irradiation irrespective of the type of resin.

Modeling of a cylindrical laminated veneer lumber II: a nonlinear finite element model to improve the quality of the butt joint

The use of low-grade logs to build spirally wound laminated veneer lumber (LVL) has been studied and improved from the point of view of the gluing process, fiber orientation angle, and end joint of the LVL. The butt joint appears to be the fracture point when the column is submitted to a compressive or bending load. Owing to the complexity of cylindrical LVL, we used a finite element method to simulate the mechanical behavior of part of its wall. This part was small enough to be considered flat but was representative of the structure, especially in the area of the butt joint. This allowed us to test the validity of different settings of the parameters involved in the manufacturing process. To feed data for this model, we used the results established for the linear and nonlinear behavior of raw hinoki in Part I of this series of articles. We then used this numerical model to improve the quality of the butt joint by testing different settings of the joint. We show that reducing the butt joint gap under 0.5 mm, which requires only a few changes in the production line, provides an important increase in the modulus of upture and nonnegligible improvement of the modulus of elasticity compared to that for a ≥ 1 mm butt joint gap.

Modeling of a cylindrical laminated veneer lumber I: mechanical properties of hinoki (Chamaecyparis obtusa) and the reliability of a nonlinear finite elements model of a four-point bending test

The weak point of cylindrical laminated veneer lumber (LVL) when its structure, used as a column in buildings, is submitted to compressive or flexural loads is the butt joint. To improve the understanding of the behavior of this complex structure, a finite elements analysis was used, which required linear and nonlinear mechanical properties to be input in the model. This article is the first of a series of reports concerning the determination of such properties, in this case hinoki (Chamaecyparis obtusa), which has been chosen for the purpose of the study. We used various methods to establish the elastic coefficients, viscoelastic parameters in three orthotropic directions, and plastic behavior in a direction parallel to the grain. As there are few references about the mechanical properties of this species, even in the elastic domain, we had to use a statistical model based on density to discuss the results obtained in the elastic domain. Then a finite element method model of a standard four-point bending test was set up to verify that the nonlinear mechanical models used for computation give accurate results that match those of the experiments.

Compression behaviors of acetylated wood in organic liquids. Part II. Drying-set and its recovery

Unmodified and acetylated cedar wood specimens were swollen in various liquids and dried under radial compression. Two stress relaxation processes were observed during drying, and the second process observed below the fiber saturation point was responsible for the drying-set and the temporary fixation of compressive deformation. The fixed shape of acetylated wood was partly recovered by soaking it in water and toluene and completely recovered in acetone. The effective shape fixation and recovery of toluene-swollen samples implied that the intermolecular hydrogen bonding was not necessary for the drying-set of acetylated wood. The degree of shape recovery was not explained by initial softening, while the acetylated wood always exhibited greater recoverability than unmodified wood. Although 85% stiffness was lost after large compression set and recovery of unmodified wood, such a stiffness loss was limited to 39% when the acetylated wood was processed with organic liquids. This indicated that the swelling of the hydrophobic region in the acetylated wood was effective in preventing mechanical damage due to large compressive deformation.

Preservative Leaching from Copper Azole–Treated Lumber: A Comparison between the Full-Cell Method and the Passive-Impregnation Method

This study investigated the leaching of copper azole (CA-B) preservative, according to JIS K 1571 standard, from sundri (Heritiera fomes Buch.-Ham.) lumber treated by full-cell and passive-impregnation methods. Although the preservative retention was similar for both methods, penetration was higher with the passive-impregnation method (66%) than with the full-cell method (43%). Further, it was found that the leaching of preservative was significantly higher in wood treated by the full-cell method (1.18%) than by the passive-impregnation method (0.92%).

Compression behaviors of acetylated wood in organic liquids. Part I. Compression in equilibrium conditions

The radial compression behaviors of acetylated cedar wood were measured in various liquids. The compressive Young’s modulus (E) of acetylated wood was reduced by soaking in water, toluene, and acetone, but it was always greater than that of water-swollen unmodified wood at the same swelling level. The behaviors of acetone-swollen unmodified wood were similar to those of acetylated wood rather than those of water-swollen unmodified wood. These results indicated that the swelling of hydrophobic wood components had a lesser influence on the E of wood than the water-swelling of unmodified hydrophilic components. After large compression (ε > 45%), a part of the strain remained unrecovered because of irreversible mechanical deformation. Since the remaining strain was smaller in the wood specimens indicating greater stress relaxation, it was assumed that the viscoelastic deformation of amorphous matrix components is important for lesser irreversible deformation and effective shape recovery of wood. In contrast with water-swollen unmodified wood, the acetylated wood and acetone-swollen unmodified wood exhibited greater shape recovery despite their relatively higher E. This suggested that the swelling of hydrophobic wood components reduced the viscosity of the matrix rather than its elasticity, resulting in more effective shape recovery with lesser softening.