This study presents anatomical characteristics, mechanical properties, microfibril angles (MFAs) and Klason lignin contents of leaf-sheath fibrovascular bundles from 14 palm genera (18 species). Observed by light microscopy, all fibrovascular bundles consisted equally of thick-walled sclerenchyma fibers and vascular tissue, while the shape and localization of vascular tissues on the transverse sections varied among species. It was possible to group these fibrovascular bundles into 3 types based on the vascular tissue’s differences: type A – rounded in the central region; type B – angular in the marginal region; and type C – aliform in the central region. These three anatomical types of fibrovascular bundles showed some correlation with a current phylogenetic classification of palm species. Through mechanical tests, this research confirmed the correlation between diameter and mechanical properties of the fibrovascular bundles of palms; tensile strength and Young’s modulus showed a decreasing trend with increasing diameter. We clarified that this trend was due to a marked increase in the proportion of transverse sectional area comprised by vascular tissue with increasing diameter of fibrovascular bundles. The MFAs of fibrovascular bundles ranged from 10.3º to 47.1º, which were generally larger than those of non-woody plants, conifers, and broad-leaved trees. The Klason lignin contents of palm species were also high, ranging from 18.3% to 37.8%, with a mean value of 29.6%. These large MFAs and high lignin contents could lead to the long-term plastic deformation and relatively low tensile strength of palm fibrovascular bundles.
To assess the characteristics of tension wood (TW) in Trochodendron aralioides Sieb. et Zucc., seedling stems were artificially inclined at angles of 30° (TW- 30), 50° (TW-50), and 70° (TW-70) from the vertical. At all angles, the growth promotion was pronounced on the upper side of the inclined stems, where excessive tensile growth stress was observed. A gelatinous layer (G-layer) formed in the tracheids of TW. The cell wall structure of the tracheids in TW was S1 + G. The G-layer had a small pit aperture angle <10°. TW-50 showed larger tensile growth stress, a thicker G-layer area, and a smaller pit aperture angle of the Glayer than TW-30 and TW-70. Lower levels of Klason lignin and hemicellulose and higher levels of α-cellulose content were observed in TW-50. In addition, an increase in glucose content and a decrease in xylose content in holocellulose were observed in TW-50. Therefore, it can be concluded that the degree of TW varied with different inclination angles.
The anatomy and the physical, mechanical, acoustical and chemical properties of pernambuco wood (Caesalpinia echinata Lam.) were investigated to determine factors that could explain the different quality of sticks used in bow manufacture. Eighteen sticks were classified into four classes (A to D with A being the best) according to their potential quality for bow manufacture. Selection of samples was based on the experience of a bow maker and on some nondestructive tests. The A-class sticks had a lower frequency of vessels and rays and a higher percentage of fibers when compared to the other classes. They also had higher values of density, speed of sound propagation, modulus of elasticity and modulus of rupture. Klason lignin content was higher in the A-class sticks but the quantity of hydrosoluble and ethanol/benzene soluble extractives was lower. The values of density and speed of sound propagation obtained by nondestructive and destructive methods were similar showing the applicability of the former in the prior selection process of the sticks.
A theoretical model was built predicting the relationship between microfibril angle and lignin content at the Angstrom (Å) level. Both theoretical and statistical examination of experimental data supports a square root transformation of lignin to predict microfibril angle. The experimental material used came from 10 longleaf pine (Pinus palustris) trees. Klason lignin (n=70), microfibril angle (n=70), and extractives (n=100) were measured and reported at different ring numbers and heights. All three traits were strongly influenced by ring age from pith while microfibril angle and extractives exhibited more of a height effect than lignin. As such, the multivariate response of the three traits were different in the axial direction than the radial direction supporting that care needs to be taken when defining juvenile wood within the tree. The root mean square error of calibration (RMSEC) for microfibril angle of the theoretical model (RMSEC = 9.8) was almost as low as the least squares regression model (RMSEC = 9.35). Microfibril angle calibrations were also built from NIR absorbance and showed a strong likeness to theoretical and experimental models (RMSEC = 9.0). As a result, theoretical and experimental work provided evidence that lignin content played a significant role in how NIR absorbance relates to microfibril angle. Additionally, the large variation in extractives content coupled with sampling procedure proved important when developing NIR based calibration equations for lignin and microfibril angle.
Structural heartwood characteristics for Prosopis laevigata (Humb. & Bonpl. ex Willd.) M.C. Johnst., including a histometrical evaluation, were obtained by light microscopy coupled with a digitised image analysis system. The growth ring boundaries of the semi-ring-porous or diffuseporous wood are often marked by a marginal parenchyma band. Average fibre length is 975 μm, the fibres are thick-walled with a single cell wall thickness of 13 μm on average. Average diameter of the vessels which are arranged in non-specific patterns differs significantly between earlywood (116 μm) and latewood (44 μm). The topochemical distribution of lignin and phenolic deposits in the tissue was investigated by means of scanning UV microspectrophotometry (UMSP). Thereby, in heartwood tissue the deposition of extractives in vessels, pit canals, parenchyma cells, fibre lumina and partly also in the S2 layers of the fibres was detected. Monosaccharides were qualitatively and quantitatively determined by borate complex anion exchange chromatography. Holocellulose content is between 61.5 and 64.7% and Klason lignin content between 29.8 and 31.4%. Subsequent extraction of the soluble compounds was performed with petrolether, acetone/water and methanol/water by accelerated solvent extraction (ASE). Total extractives content in heartwood ranges between 14 to 16% on a dry weight basis. Major compounds in acetone/water extracts were identified as (-)-epicatechin, (+)-catechin and taxifolin, and quantitatively determined by liquid chromatography (RP-HPLC-UV).
The fiber bundles from the lignified leaf sheath of windmill palm (Trachycarpus fortunei) are widely used as natural fibers for various products, and exhibit excellent durability. In this study, the cell wall of windmill palm fibers was characterized using transmission electron microscopy, high resolution field emission scanning electron microscopy, and polarized light microscopy, and chemical analysis to measure lignin content. It was found that (1) the secondary wall was composed of just two layers, outer (equivalent to S1, 0.65 ± 0.12 μm) and inner (equivalent to S2, 1.28 ± 0.30 μm) ones, with a high ratio of S1 to the whole cell wall thickness; (2) the microfibrils of the S1 are orientated in an S-helix (MFA, 127.0° ± 2.0), and those of the S2 in a Z-helix (MFA, 43.7° ± 2.2); and (3) the Klason lignin content of fiber bundles was very high (nearly 40%). It is suggested that these structural and chemical features of windmill palm fibers are involved in their mechanical properties such as high flexibility and elasticity, and also related to their high durability.
We examined the effects of polyphenols on the analysis of lignin by histochemical methods, namely, the Mäule color reaction coupled with microspectrophotometry and ultraviolet microspectrophotometry, in wood of Eucalyptus camaldulensis and E. globulus. Thin sections and wood meals were extracted with solutions of alkali at different concentrations. The amounts of alkali-soluble extractives increased with increasing concentrations of NaOH. By contrast, there was no clear correlation between amounts of Klason lignin and the concentration of NaOH. The visible-light absorption spectra of cell walls of all woody tissues from both species changed after alkali extraction. In particular, the spectra of cell walls of vessel elements changed considerably, even when only a dilute solution of alkali was used. Ultraviolet absorption spectra did not show clear changes after extraction with alkali. These results indicate that polyphenols in cell walls affect the results of histochemical analysis. Therefore, a preliminary extraction with alkali, namely, extraction with a 1% solution of NaOH, is needed to assess the precise distribution of lignins in the cell walls of Eucalyptus wood by histochemical methods. The cell walls of wood fibers of Eucalyptus camaldulensis contained both guaiacyl and syringyl units and those of vessel walls contained mostly guaiacyl units. However, the cell walls of wood fibers in Eucalyptus globulus contained mainly syringyl units, while those of vessel elements contained both guaiacyl and syringyl units. Syringyl-type polyphenols, which have spectra similar to those of syringyl-type lignins, were found in the cell walls of wood fibers and vessel elements and in cell corners among wood fibers in both species of Eucalyptus.