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The delayed recovery of the longitudinal length in biomechanically pre-stressed wood, specifically tension wood with a conspicuous gelatinous layer in the cell wall structure, was generally induced by hygrothermal treatment. However, hygrothermal treatment should not be the sole method to induce delayed recovery in tension wood. In order to broaden our understanding of the mechanism underlying delayed recovery, tension wood of Quercus serrata was treated by drying and subsequent rewetting over many times. Interestingly, the longitudinal deformation over repeated drying and subsequent rewetting treatments (dry-wet treatments) was identical to the response of the tension wood during repetitive hygrothermal treatments. Hence, the longitudinal delayed recovery in pre-stressed tension wood was concluded to be induced not only by hygrothermal treatment but also by the dry-wet cycles. [ABSTRACT FROM AUTHOR]

Increasing interest in understanding tension stress generation in tension wood with fibres having a gelatinous layer (G-layer) has focused attention on the specific role of this layer. To distinguish its contribution from those of other wall layers, the G-layer of wood sections was isolated by ultrasonication. The aim of this study was to assess the effect of sectioning and of the ultrasonic treatment on the mesoporosity of tension wood using nitrogen adsorption-desorption analysis. The results showed that the process of isolating the G-layer using ultrasonication strongly affects its mesoporosity. Most damage was found to occur during sectioning rather than as a result of the 15-min ultrasonic treatment. [ABSTRACT FROM AUTHOR]

A reconstruction of historical timber structures requires precise diagnostics of mechanical properties of particular structural members, which would subsequently underlie a reliable plan of the reconstruction. Mechanical properties of wood are determined most exactly using destructive techniques, but often they cannot be used in historical constructions. This calls for using nondestructive or semi-destructive techniques that are still reasonably exact, not too invasive and can be profitably used in situ. This work examines a new nondestructive diagnostic tool that enables to determine strength and stiffness parameters of wood parallel to the grain in situ. The function of the instrument was verified using standard compression tests parallel to the grain that correlated with the instrument well ( r = 0.92). Complicated stress state in the drilled hole was examined by contact finite element analysis and revealed high contribution of longitudinal elastic moduli in force measurement ( r = 0.96). [ABSTRACT FROM AUTHOR]

The carbonization characteristics of tension wood (TW) and compression wood (CW) from Paulownia tomentosa and Pinus densiflora branch woods, respectively, were investigated and compared to those of opposite wood (OW) and lateral wood (LW). The carbonization was conducted at 400, 600, and 800 °C. Heating values, pH, char yields, cell wall structures, and combustion characteristics were different in TW and CW, whereas only little differences were found among reaction wood, OW, and LW. The heating values of TW charcoal were lower than those of CW charcoal at 400 and 600 °C, while the pH of TW charcoal was higher than that of CW at all carbonization temperatures. The char yields of CW were the highest among all the samples at all carbonization temperatures. Furthermore, the TW charcoal was more thermally stable than CW charcoal. SEM observations revealed significant differences in the cell wall structures of the woods before and after carbonization. The gelatinous layer in TW disappeared, and the helical cavities and intercellular spaces in CW persisted throughout the carbonization process. The cell wall structures of the wood samples became smooth and amorphous as the carbonization temperature increased. [ABSTRACT FROM AUTHOR]

When a green wood specimen is hygrothermally treated, it often shows dimensional changes in the longitudinal and transversal directions, which is called hygrothermal recovery of wood. Hygrothermal recovery of tension wood is assumed to be behind the unusual contraction of gelatinous layer along the longitudinal axis. This study investigated whether hygrothermal recovery of tension wood was temperature-dependent. Hygrothermal treatment at 80, 100 and 120 °C was given to green Quercus serrata tension wood, and longitudinal and tangential dimensions were recorded. In the longitudinal direction, the trend line obtained after 10 times of 10-min hygrothermal treatments at respective temperatures unraveled that it was comprised of initial recovery and continuum contraction at 100 and 120 °C, but no initial recovery was recognized at 80 °C. In the tangential direction, both the initial and the continuum deformations were expansive, and initial recovery was smaller at 80 °C. The results of multiple comparison test revealed that the parameters characterizing the trend line differed significantly among three temperature sets. Further, the result highlighted the existence of breakage of hygrothermal recovery mechanism at temperature between 80 and 100 °C. [ABSTRACT FROM AUTHOR]

Tension wood, when kiln-dried, is likely to deform hugely, which is probably caused by a gelatinous layer of the gelatinous fiber. To elucidate the mechanism behind the deformation of tension wood during kiln-drying, the strains experienced by tension wood during a hygrothermal treatment that is akin to an early stage of kiln-drying were investigated. Normal wood elongated along the longitudinal axis after the first treatment and leveled off with repetitive treatments. During the first treatment, tension wood contracted significantly along the longitudinal axis, followed by small subsequent contractions, which occurred during successive treatments. This characteristic hygrothermal behavior of tension wood correlated with the areal ratio of the gelatinous layer. One of the possible reasons why tension wood behaves differently was thought to be particular behavior of gelatinous layer. This finding will contribute to the development of appropriate seasoning method for tension wood by clarifying the mechanism behind the deformation of the gelatinous layer. [ABSTRACT FROM AUTHOR]

Mechanical tests on micro-samples were performed in the three material directions in normal, opposite, and tension wood collected from a poplar tree. Two custom micro-devices were designed and built in the laboratory to test samples under pure tension in the transverse direction and under 4-point bending conditions in the longitudinal direction. Both devices were designed to handle samples with a small transverse section (a few square mm), which allowed to select zones with homogenous anatomical features. The results indicate a very high longitudinal stiffness in tension wood (up to 35 GPa compared to an average of 18 GPa for normal wood). Considering wood density, the value represents a specific modulus that is nearly 70 % crystalline cellulose. However, tension wood is slightly less stiff in the tangential and radial directions (1,150 vs. 1,500 MPa for normal wood in the radial direction and 430 vs. 530 MPa in the tangential direction). [ABSTRACT FROM AUTHOR]

Using confocal microscopy, tracheid wall organisation was investigated with pontamine fast scarlet 4B (P4B), a cellulose-specific stain that fluoresced red following green excitation. P4B fluorescence was present throughout unlignified walls (cambium, ray cells, resin canals and parenchyma cells) and in two concentric bands around opposite and compression wood tracheids. Scanning electron micrographs demonstrated these bands as the S1 and S3 layers of normal wood, and the S1 and inner S2 layers of compression wood. Fluorescence was also strongly dependent on the polarisation of the excitation light, a phenomenon referred to as bifluorescence. Compared to two other cell wall stains, Congo red and calcofluor white, P4B showed a higher specificity for the S1 and S3 layers and increased bifluorescence. These results suggest that P4B is an ideal tool with which to investigate the orientation of cellulose microfibrils in the S1 and S3 layers of the tracheid wall. [ABSTRACT FROM AUTHOR]

Growth strains were measured in situ in nine trees of three species from a French Guiana tropical rainforest in a clearly active verticality restoration process. The aim was to detect tension wood within the samples. Wood specimens were cut in the vicinity of the growth strain measurements in order to determine the microfibril angle and some mechanical and physical properties. As suspected, tensile growth strain was much higher in tension wood zones, as shown by the slightly higher longitudinal modulus of elasticity. Conversely, tension wood showed reduced compression strength. Longitudinal shrinkage was much higher in tension wood than in opposite wood. Clear relationships between the microfibril angle and longitudinal properties were noted in comparison (i) with those observed in gymnosperm compression wood and (ii) with expected relationships from the organization of wood fibres cell wall structure. [ABSTRACT FROM AUTHOR]

Abstract  The behaviour of longitudinal shrinkage was investigated in the corewood of a swept, 17-year-old New Zealand radiata pine stem. Wood categories in terms of normal wood, mild compression wood and severe compression wood were identified microscopically using autofluorescence of lignin. Average longitudinal shrinkage was collated according to corewood location and wood category within corewood in the leaning and the vertical parts of the stem, and then maximum radial difference of longitudinal shrinkage within growth ring was examined. The results show that the average longitudinal shrinkage is significant (2.4%) in the corewood of the leaning part of the stem. Among wood categories, severer compression wood displays the highest (2.9%) average longitudinal shrinkage. In the context of this study, growth rings may consist of one of three types of wood: (1) only normal wood; (2) a single compression wood type; and (3) mixed-type wood. Where multiple compression woods co-existed with normal wood, the maximum radial difference of longitudinal shrinkage within the growth ring was found to be 4.0%. A strong correlation (R 2 = 0.90) between average MFA and average longitudinal shrinkage suggests a significant influence of the average MFA on average longitudinal shrinkage across the three growth ring types. [ABSTRACT FROM AUTHOR]