Showing papers by "Masato Yoshida published in 2012"

Proposed supramolecular structure of lignin in softwood tracheid compound middle lamella regions

Abstract: Abstract The structure of lignin in the compound middle lamella (CML) of softwood tracheids differs from that in the secondary wall (SW) in regard to the content of condensed structures (5-5′-biphenyl, dibenzodioxocin and 4-O-5′-diphenyl ether). In an early stage of cell wall formation, random coarse networks composed of thin cellulose microfibrils (CMFs), hemicelluloses, and pectin are formed in the CML, then globular p-hydroxyphenyl/guaiacyl lignin (HG-lignin) is deposited quickly into the network. The globular lignin is assumed to be a micellar aggregate of oligolignols folded at the β-O-4 bond with their phenolic ends on the outer part of the aggregate. When 3D clusters of the globules are deposited on the preformed network of polysaccharides, further growth of the oligolignols by endwise addition of new monolignols is spatially limited, so frequent condensation occurs between growing aromatic ends of adjacent HG-oligolignols within the globule and between the wide contact boundaries of the 3D clustered globules to produce a highly condensed supramolecule in CML. In SW, the folded G-oligolignols are deposited slowly in the narrow tubular space surrounding thick CMFs coated with hemicelluloses. Condensation occurs mostly between adjacent growing ends of the oligolignols within the tubular aggregates. Spatial regulation of condensation of folded polylignols is one of the factors producing a different supramolecular structure for CML lignin than for SW lignin.

Mechanical interaction between cellulose microfibrils and matrix substances in wood cell walls induced by repeated wet-and-dry treatment

Abstract: We measured the lattice spacing of the cellulose in sugi (Cryptomeria japonica D. Don) and hinoki (Chamaecyparis obtusa Endl.) cell walls under wet and dry conditions. We gave all specimens repeated wet-and-dry treatments and tried to induce substantial changes in the microstructure of the wood cell wall. Macroscopic dimensions, measured using a micrometer, showed well-known behaviors, that is, shrinkage by drying and swelling by wetting, which were unaffected after the repeated wet-and-dry treatments in both longitudinal and tangential directions. On the other hand, lattice spacing, measured using an X-ray diffractometer, showed different results. In particular, d 200 lattice spacing expanded considerably with drying in the early stages of repeated wet-and-dry treatments. The d 200 lattice spacing in the dried specimen then became gradually smaller in the later stages, whereas no such dynamic change was observed in d 004 lattice spacing throughout the repeated wet-and-dry treatments. Once the d 200 lattice spacing in the dried specimen had become smaller after giving wet-and-dry treatments, it did not recover, even after soaking in distilled water for 1 month. These results suggest that repeated drying and re-swelling caused structural changes in the wood cell wall, specifically an interfacial separation between cellulose microfibrils and matrix substances.

Anatomical and chemical factors affecting tensile growth stress in Eucalyptus grandis plantations at different latitudes in Brazil

Abstract: The key to using planted Eucalyptus as timber lies in controlling the characteristic high tensile growth stress that often causes serious processing defects in sawn logs and lumber. In the present study, we investigated variations in the lon- gitudinal released strain (RS) of surface growth stress in stems of Eucalyptus grandis W. Hill ex Maiden planted in a wide range of latitudes in Brazil and established relationships between RS measurements and anatomical and chemical factors. Cellulose and lignin content, RS, and the microfibril angle (MFA) of the middle layer of the secondary wall (S2 layer) dif- fered among latitudes. The increase in cellulose content and decrease in MFA were correlated with the contractive value of RS, which explained the higher tensile growth stress in stems from high-latitude plantations where higher cellulose content and lower MFA were observed. To reduce processing defects due to tensile growth stress, the factors controlling MFA val- ues and cellulose content must be identified. Resume : Pour utiliser l'eucalyptus comme bois d'œuvre, la cle consiste a maitriser les fortes contraintes de tension caracte- ristiques liees a la croissance et qui causent souvent de graves defauts lors de la transformation des billes et du bois scies. Dans cette etude, nous avons examine la variation des deformations longitudinales (DL) dues au relâchement des contraintes de croissance en surface dans le tronc d'Eucalyptus grandis W. Hill ex Maiden plante sous un vaste eventail de latitudes au Bresil et nous avons etabli des relations entre les mesures des DL et les facteurs anatomiques et chimiques. La teneur en cel- lulose et en lignine, la valeur des DL et l'angle des microfibrilles (AMF) de la paroi S2 variaient selon la latitude. L'aug- mentation de la teneur en cellulose et la diminution de l'AMF etaient correlees avec la valeur contractile des DL, ce qui explique que les contraintes de tension liees a la croissance sont plus importantes dans les tiges provenant de plantations dont la latitude est plus elevee, ou une teneur en cellulose plus elevee et un AMF plus faible ont ete observes. Pour reduire les defauts dus a la transformation, il faut identifier les facteurs qui determinent l'AMF et la teneur en cellulose. (Traduit par la Redaction)