Lignin is a complicated biopolymer which exists in the wood cell wall. Many model compounds that mimic substructures of lignin have been synthesized. They have been used and played an important role in the various fields of wood research. This paper summarizes the synthesis of lignin model compounds, and describes some examples of their use in wood research. In particular, this review focuses on recent progress in the synthesis of lignin model compounds. Furthermore, the synthesis of β-O-4 type artificial lignin polymers by the author is also briefly introduced.

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To promote the use of sugi woods, the information on the variation of wood properties is very important. Obi-sugi is a major group of sugi cultivars planted in Southern Kyushu. However there is no information on the variation of wood properties with height position in the stems of Obi-sugi trees. We examined in detail the difference between the wood properties at 5 m above ground (upper height position) and those at 1.5 m above ground (lower height position) of Obi-sugi cultivars. Obtained results were as follows : Mechanical properties in both mature and juvenile wood at the upper height position were higher than those at the lower height position in most cultivars. Radial variations of mechanical properties at the upper height position were larger than those at the lower height position in most cultivars. Microfibril angle of latewood tracheids (MFA) in both mature and juvenile wood at the upper height position was smaller than those at the lower height position in most cultivars. On the other hand, basic density and latewood tracheid length in both mature and juvenile wood at the upper height position did not differ from those at the lower height position in many cultivars. Higher mechanical properties at the upper height position were mainly the result of the decrease of MFA with height position. In addition, to examine the whole tree variation from top to bottom, we investigated the variation of wood properties of Obi-sugi trees at different height increments. The results suggested that longitudinal variations of mechanical properties were well explained by variations of MFA and basic density, and that height increment affected the mechanical properties and the longitudinal variation pattern of wood properties.

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We made timber portal frames composed of compressed LVL beam-to-column joints and steel column-to-base joints. The former used compressed LVL plates and compressed LVL pins and the latter used steel plates and compressed LVL pins/steel pins (B1/B2 type). In the moment applying test, the compressed LVL beam-to-column joints showed little initial-slip and good ductility, but the steel column-to-base joint showed large initial-slip and poor ductility. In the racking tests of timber portal frames, the moment was distributed to each joint by the ratio of the rotational rigidity, and the beam-to-column joints yielded first, followed by yielding of the column-to-base joints. The maximum resistance of the timber portal frame was decided by the resistance of the column-to-base joints, and also the failure mode was decided by the characteristic failure of the column-to-base joints. The allowable shear strength of B1 and B2 type timber portal frames was 8.0 kN and 11.9 kN respectively. The height of the inflection point of the timber portal frame calculated by Inayama's formula showed significant correlation with the experimental values calculated by the distribution of the degree of strain, and the resistance and the deformation could be predicted by this formula.

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Shear creep property of wooden I-beams of 235 mm depth and three flange sizes with Todomatsu (Abies sachalinensis) lumber and Karamatsu (Larix kaempferi) plywood was examined by bending creep tests with a 3.8 m span and shear creep tests with a 1.2 m span. Three replications of each flange size and each creep test were used and conditioned at 20°C and 65% RH. All creep tests were carried out under uncontrolled temperature and humidity. Bending loads were applied to each beam for 35 days. Each load was determined at a stress level of 33% of the average ultimate loads from static rupture tests of end-matching specimens. Test results and analyses showed that the average relative creep after 50 years load-duration (i.e., apparent bending creep factor) would be about 1.4 times the initial deflection of bending creep tests, and about 1.8 times the initial deflection of shear creep tests. This result indicated that creep deflection would be greater for the I-beams with a higher ratio of the shear component to the total deflection. A separation method of pure bending and shear creep factor was derived from two apparent bending creep factors of bending and shear creep tests. Using this method, it was predicted that the pure bending creep factor would be about 1.3 times the bending component of the initial deflection and the shear creep factor would be about 2.0 times the shear component. Simulation in various load conditions indicated that the prediction method of creep deflection using those separated creep factors would be practically applicable for reasonably calculating the creep deflection of I-beams in any condition.

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In order to develope a rational joint system in traditionally joined timber frame structures, we designed a new drift-pin joint composed of a steel pipe drift-pin with a glass-fibre-reinforced nylon (GFRP) plate inserted into a slit of the timber. Lateral resistance tests of the joint with a single drift-pin were conducted to evaluate the effects of dorift-pin shape on maximum and yield loads. These properties were compared with a common drift-pin joint with a steel plate. The joint with a nylon plate had 60% of the stiffness, 90% of the maximum load and 90% of the yield load as compared to a steel plate. Both nylon and steel plate joints with steel pipe drift-pins had 80% of the lateral strength of common drift-pins. Maximum and yield loads of nylon plate joints with steel pipe drift-pins under reversed cyclic loads were equivalent to those under monotonic loads, and no failure of nylon plate had occured under reversed cyclic loads at the yield resistance level after 150 cycles.

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A new drift-pin joint consisting of a glass-fibre-reinforced nylon (GFRP) plate inserted into a slit of the timber with steel pipe drift-pins was designed. In the previous report, basic shear properties of the joint with a single drift-pin were examined. In this report, various types of GFRP timber frame joints were subjected to tension and shear resistance tests, and strength properties were evaluated in comparison with those of traditional timber joints and metal connected timber joints. The estimated allowable strength of column-to-sill joints obtained by vertical pull-up tests was 15.3 kN. The value was higher than that of nailed joints with steel side plates (VP : Z marked connector) but the average value of initial stiffness was lower. The estimated allowable strength of girder-to-beam joints obtained by shear resistance tests was 20.7 kN. The value was lower than that of dovetail joints but average values of maximum load, initial stiffness, yield strength and ultimate strength were higher. The estimated allowable strength of column-to-girder joints in shear resistance tests was 28.1 kN. The result was affected by brittle failure due to fracture of GFRP plates and the value was lower than that of beveled dado joints, but average values of initial stiffness, yield strength and ultimate strength were higher.

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We investigated chemical characteristics of wood materials such as Abies sachalinensis sawdust and Acacia mangium mechanical pulp treated with an ionic liquid, 1-n-butyl-3-methylimidazolium chloride ([C₄mim] Cl). The residue from both Abies sachalinensis sawdust and Acacia mangium mechanical pulp treated with [C₄mim] Cl decreased with increasing temperature and time. The dissolution behavior of Abies sachalinensis sawdust and Acacia mangium mechanical pulp toward [C₄mim] Cl at 120°C was similar. On the other hand, FT-IR spectra of Abies sachalinensis sawdust treated with [C₄mim] Cl showed a decrease of the peak at 1050 and 896 cm^-1 from carbohydrates such as cellulose and hemicellulose in wood, and an increase of the peak at 1507 and 858 cm^-1 from the lignin. In addition, glucose in the Acacia mangium mechanical pulp treated with [C₄mim] Cl decreased rapidly, although the lignin contents increased. Thus, these results indicate that the dissolution rates of carbohydrates such as cellulose and hemicellulose in wood components are much faster than that of lignin. Consequently, the lignin is clarified to be concentrated in the residue by the dissolution of wood material in [C₄mim] Cl.

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