The 3D macromolecular structure (supramolecular structure, SMS) of lignin in different morphological regions of the cell wall is widely diverse in many respects: (1) type and frequency of monomer (p-hydroxyphenyl(H)-, guaiacyl(G)- and syringyl(S)-propane) units, (2) type and frequency of inter-unit bonds, (3) shape, size, and (4) linkages between lignin and polysaccharides. This diversity is found also in different kinds of cells of different plant species. The causes of the complicated heterogeneity of lignin SMS can be understood reasonably well from the viewpoints of evolutionary biology and polymer chemistry: “ontogenesis recapitulates phylogenesis”, and growing of lignin SMS is controlled by the supply of monolignols and polymerization conditions provided by previously deposited polysaccharides. The first land plants emerged with lignified vascular tissue having excellent capabilities in conduction of aqueous material and mechanical support of the plant stem and branches. Lignin played a multifunctional role in making the tracheid wall hydrophobic and mechanically strong, and very defensive against biodegradative microbes by formation of structurally heterogeneous SMS. A cluster of globular HG lignin consisting of condensed oligolignols effectively protects weak β-O-4′ bonds located inside the lignin SMS from biodegradation by exogenous enzymes or other active agents. For Pteridophyta and gymnosperms, the first dominant vascular plants with HG lignin, this resulted in longevity of huge plants and slow alternation of generations around the Carboniferous period. Changes of the environment on earth promoted the evolution of angiosperms in which multifunctional tracheids differentiated into conduction-specialized vessels and support-specialized fibers. The excessively strong defense function of HG lignin became moderate in less condensed SG lignin, and the weakened defense rendered cell walls of angiosperms biodegradable easily after plant death to provide space for growing of young plants and frequent alternation of generations. Lignin in Gramineae containing ester-bonded ferulic and p-coumaric acids is highly biodegradable. Thus, angiosperms with lignin of appropriate defense function evolved by the ready adaptability to environmental change on earth through frequent gene conversion. Additional factors promoting evolution of lignin structure are proposed.

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Wari-kusabi Joints (Japanese traditional mortise-tenon joints with wedges) have been used as wooden structure joints in Japan. The pull-out resistance mechanism of the joint which connects post to beam was analyzed and modeled based on mechanical theory. The load-deformation curves in pull-out tests of mortise-tenon joints were influenced by resistance of compressive strain inclined to the grain and friction between post and beam. We proposed a mechanical model including these factors. The load-deformation curves in the elastic and plastic region could be estimated; initial stiffness K, and yield point deformation δ_y were calculated by proposed design formula.

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Particleboards were manufactured from high-moisture raw particles using a radio-frequency press which has both hot-press heating and radio-frequency heating, and the properties of the boards were analyzed. The pressing time was at least 8 min and the internal bond strength was 0.192 MPa when the boards were manufactured using only hot press heating without radio-frequency heating. However, a reduction in pressing time to just 3 min and an increase in internal bond strength to 0.440 MPa was possible when the board was manufactured using the radio-frequency press. Using the radio-frequency press caused the temperature of the inside of the boards to rise sharply and this resulted in a great reduction in pressing time and an increase in internal bond strength. Moreover, the pressing time was reduced to 2.5 min and the internal bond strength was increased to 0.552 MPa by installing an air-injection device on the radio-frequency press. Further reduction of pressing time and increase in internal bond strength were achieved by air injection. As a result, it was clarified that the internal bond strength of the boards could be achieved even when the binder resin content was reduced by approximately 25%.

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The optimal conditions of compression processing in a short time and with low energy using hot-pressing to improve surface hardness of Sugi (Cryptomeria japonica) was investigated. In this study, after boards of Sugi of sapwood and heartwood were conditioned to approximately 10 and 25% of moisture content (MC) and compressed at temperatures of 20 to 140°C with 6 cycles of compression processing including 5 minutes pressing and 1 minute unloading, they were evaluated by recovery of compressive deformation by springback, density profile in the radial direction, observation by Scanning Electron Microscope (SEM) and Brinell hardness. From these results, the optimal condition of compression processing in this study was approximately 10% of MC, and pressing temperatures above 100°C for sapwood and at 100°C for heartwood. Density and hardness of the surface on compressed woods were kept at a high level after planer treatment. Since boards generally contain both sapwood and heartwood, the optimal condition of compression processing is considered approximately 10% of MC and at 100°C of pressing temperature. Long-term dimensional stability was not considered because compressed board is assumed to be painted right after compression processing.

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Lateral impact vibration is a simple method for diagnosing the wood quality inside a standing tree. The product d·f of the resonance frequency f of the vibration or the sound of an impacted tree stem and the stem diameter d serves as the index of the diagnosis. To study the effect of the weight of hammers on the detection of f, 21 large sample trees from among nine species were impacted by eight types of hammers (ranging in weight from 101 to 3250g). It was possible to determine f for all sample trees. Therefore, it was confirmed that this method can also diagnose the wood quality of large standing trees using the index d·f. The frequency peaks tended to be prominent in lower frequency ranges upon impact with heavier hammers. The relationship between the weight of the hammers and the power of detecting f was studied. The results indicated that the power tended to be higher with an increase in hammer weight (R²=0.54-0.99). These results show that in the diagnosis of large living trees by the lateral impact vibration method, heavier hammers were more suitable for detecting the resonance frequency f. In addition, the adequate hammer weight for practical use was discussed, considering both lightness and the power of detecting f.

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