Synthetic resin adhesives such as formaldehyde-based resins have been used for manufacturing wood-based materials. However, in view of concern about global environmental problems and potential shortages of fossil resources, it is desirable to reduce the consumption of synthetic resin adhesives. Natural adhesives derived from bio-resources have been considered as alternatives to synthetic resin adhesives. Natural adhesives for wood are classified into saccharide-based, protein-based, aromatics-based, oil-based, natural rubber-based, and liquefied wood based-adhesives, etc. Several adhesives have been investigated in each group. Recent trends of natural wood adhesives are reviewed based on published research papers. Here I would like to summarize the kinds of natural substances, research methods, synthesis methods, resin properties, bond performance and evaluation methods.

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This review focuses on synthesis methods of cellulose derivatives, in particular, those of cellulose ethers, from viewpoints of regiocontrolled introduction of protective and functional groups, published over roughly a quarter of a century. Influence of regioselective functional groups of cellulose on performance is discussed with particular focus on methylcellulose derivatives, 2-O-methyl, 3-O-methyl, 6-O-methyl, 2, 3-di-O-methyl, 2, 6-di-O-methyl, 3, 6-di-O-methyl, and 2, 3, 6-tri-O-methyl celluloses. Synthesis methods for tri-O-alkyl celluloses (carbon numbers of alkyl chain = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14 and 18), and alternatingly 2-O- and 6-O-methylated celluloses are also summarized. In addition, regioselectively functionalized cellulose esters are described. Moreover, synthesis methods of cellulosic block copolymers with other polymer blocks and diblock cellulose ethers with regioselective functionalization patterns are summarized. New insights into structure-property relationships of methylcellulose with blocky structure to form thermoresponsive hydrogels are described in detail.

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Cross-laminated timber (CLT) panels consist of several layers of lumber stacked crosswise and glued together on their faces. CLT panels are excellently applicable for timber buildings as slabs for horizontal structural members. Live load and dead load on CLT panels cause internal shear stress. Distribution of internal shear stress in CLT panels is affected by the modulus of elasticity of parallel layers. Rolling shear stress occurs in cross layers under shear force applied to CLT panels. Generally rolling shear strength is lower than the shear strength parallel to the grain. Few data of rolling shear strength of lumber exist. Internal shear capacity of several types of CLT panels was predicted by calculating the distribution of internal shear stress from the experimental rolling shear strength of sugi lumber. To verify the calculated shear capacity of several types of CLT cross sections, asymmetric four-point bending tests were carried out. The experimental shear capacity was found to be 12% lower than the average value of the rolling shear strength model for the lumber of the shear zone and was 16% higher than the minimum value of rolling shear strength model.

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To establish adequate pre-treatment for preservation, the effects of the drying method on preservative penetration and dimensional changes in treated wood were investigated using sugi (Cryptomereia japonica D. DON) boxed-heart timber. The high-temperature setting method reduces the amount of wood preservative impregnated in sugi heartwood specimens, as compared with natural and conventional drying methods. In some specimens dried with the high-temperature setting method, remarkable dimensional changes were observed on specimens without kerf due to surface checks which developed on the treated specimens during the drying process. Therefore a few of those specimens failed to meet the JAS preservative penetration requirement for sawn timber, although their surfaces were incised to increase preservative penetration.

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