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Journal ArticleDOI

Shrinkage of the gelatinous layer of poplar and beech tension wood

01 Jan 2001-Iawa Journal (Brill)-Vol. 22, Iss: 2, pp 121-131
TL;DR: In this article, the authors showed that longitudinal shrinkage is much greater in the gelatinous layer than in other layers of beech and poplar tension wood than in normal wood, due to mechanical interactions of cell wall layers.
Abstract: Macroscopic longitudinal shrinkage of beech and poplar tension wood is higher than in normal wood. This shrinkage is the result of mechanical interactions of cell wall layers. SEM observation of cut, dried surfaces showed that longitudinal shrinkage is much greater in the gelatinous layer than in other layers. AFM topographic images of the same cells, both in water and in air-dry conditions, confirm this result. Measurements on sections indicate around 4.7% longitudinal shrinkage for the G layer.

Summary (1 min read)

Longitudinal shrinkage in wood

  • Like all other wood properties, hygroexpantion presents a very important anisotropy.
  • The knowledge of the wood cell structure, as a multi-layer fibre composite, allows the modelling of the longitudinal shrinkage.
  • A high local level of growth stress is always related to presence of tension wood (Trénard & Guéneau 1975; Sassus 1994).
  • Finally a last superficial planning is done manually with a brand new razor blade in order to produce a nice transverse surface, the sample being always kept in moist condition.

Scanning electron microscopy

  • Both in poplar and beech, one cell is observed with two angle of view, at first perpendicular to the surface and then tilted 70° from that direction (Fig. 8).
  • The x coordinate is given directly by the first image while the y coordinate can be calculated with equation 1 using both images (Fig. 7).
  • These topographic profiles allow measurements of differential shrinkage between cell wall layers.
  • Thin sections Several poplar cells were observed after drying.
  • Mean measurements of differential restraint between G layer and compound middle lamella (CML) are 1.99 µm for a face, 1.83 µm for the other and 3.82 µm for the sum of faces.

Atomic force microscopy

  • The profile in water (Fig. 11 A') shows that there is already a small retract of Glayer before drying.
  • The profile in water after 2 hours in 80°C water (Fig. 11 B') shows very few additional retract of G-layer before drying.
  • The profile in air-dry conditions (Fig. 11 C') confirms the presence of a more important shrinkage in G-layer than in other layers.
  • After the blade moving, due to recovery of these different stress states, softer and thinner layers lay above stiffer ones like the G-layer.
  • Again, it can be argued that this separation allows a more complete release of growth stress in the G-layer, so that, this further differential shrinkage is another expression of growth stress only.

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Shrinkage of the Gelatinous Layer of Poplar and Beech
Tension Wood
Bruno Clair, Bernard Thibaut
To cite this version:
Bruno Clair, Bernard Thibaut. Shrinkage of the Gelatinous Layer of Poplar and Beech Tension Wood.
IAWA Journal, Brill publishers, 2001, 22, pp.121-131. �10.1163/22941932-90000273�. �hal-00004542�

SHRINKAGE OF THE GELATINOUS LAYER OF
POPLAR AND BEECH TENSION WOOD
by
Bruno Clair & Bernard Thibaut
LMGC – Bois, Université Montpellier II, CC 081, Place E. Bataillon,
34095 Montpellier, France (e-mail: clair@lmgc.univ-montp2.fr).
Published in IAWA Journal, Vol. 22 (2), 2001: 121–131
SUMMARY
Macroscopic longitudinal shrinkage in beech or poplar tension wood
is higher than in normal wood. This shrinkage is the result of cell
walls layers mechanical interactions. In order to complete the basic
data with a view to modelling the cell wall, we are interested in
shrinkage differences between cell wall layers and especially of G-
layer in poplar and beech. Wood samples in green condition are cut
with a razor blade, and then dried before observation. SEM
observation shows longitudinal shrinkage much more important in
gelatinous layer than in other layers. AFM topographic images of
same cells, both in water and in air-dry conditions, confirm this result.
Measurements on thin sections allow quantitative results around 4.7 %
longitudinal shrinkage for G-layer.
Key words: cell wall, gelatinous layer, shrinkage, tension wood.
INTRODUCTION
Longitudinal shrinkage in wood
Like all other wood properties, hygroexpantion presents a very important
anisotropy. Between green condition and ovendry condition, shrinkage ranges from
0.05 % to 0.3 % in longitudinal direction, 3 % to 6 % in radial direction and from
6 % to 12 % in tangential one (Skaar 1988). According to these values, the
hygroexpension in axial direction is not apparently a problem for the user. However,
two cases exist when longitudinal shrinkage starts to be more important: in reaction
wood (tension wood of angiosperms and compression wood of gymnosperms) and
juvenile wood (Skaar 1988). In these two types of wood, axial shrinkage can reach
1 % or more (Nepveu 1994). For these woods, shrinkage value cannot be considered
as negligible, because wood beams have generally their longer distances in axial
direction. These important differences can be explained by the wood fibre structure.

2 IAWA Journal,
From wood fibre structure to shrinkage modelling
The knowledge of the wood cell structure, as a multi-layer fibre composite, allows
the modelling of the longitudinal shrinkage.
One of the first models, which is still a reference, is the Barber and Meylan 's
one (1964) refined by Barber (1968). This model considers that the cell wall is
reduced to S
2
layer. S
2
layer is described like an amorphous hygroscopic matrix in
which are imbedded parallel crystalline microfibrils which act to restrain
hygroexpention in the direction parallel to their axes (Fig. 1) (Cave 1972a). Thus,
microfibril angle is the determinant factor of longitudinal shrinkage. Low angle of
microfibril in relation to axial direction induces low axial shrinkage (like in normal
wood) and high angle allows a higher shrinkage (like in juvenile or compression
wood). Later, other models integrating other components properties (cellulose,
hemicellulose and lignin), changes in matrix behaviour during drying and
introducing the different cell wall layers have been proposed to refine this first
theory (Barrett et al. 1972; Cave 1972b, 1978; Sassus 1998; Gril et al. 1999;
Yamamoto 1999).
Matrix Microfibrils Woody mater
Fig. 1: schematic representation of the "reinforced matrix" (Sassus 1998)
These models give a good understanding of macroscopic axial shrinkage for
different values of microfibril angle, for normal, compression and juvenile wood.
However, they cannot explain the behaviour of tension wood with gelatinous
layer. In fact, in G layer, microfibril angle is very low or nil (Chaffey 2000), even
when macroscopic longitudinal shrinkage is high (Clarke 1937; Chow 1946; Sassus
1998). Norberg and Meier (1966) had isolated portion of G layer and said that they
do not show high longitudinal shrinkage. The G layer is generally loosened from S
2
layer and this latter one is very thin in tension wood. So these authors and Boyd
(1977) assume that in that case, longitudinal shrinkage is produced by S
1
layer, G
layer being unable to prevent it.
MATERIAL AND METHODS
One poplar (Populus cv I4551) and one beech (Fagus sylvatica L.), were chosen for
this study. These species are known to have characteristic tension wood with G layer
and a high macroscopic axial shrinkage.
Populus cv I4551
During the growing period, a young one year old poplar tree in a container is tilted
35° from the vertical. At the end of that period, the stem has nearly regained its
verticality by producing tension wood on the upper side (Fig. 2). Wood sample
taken from this tension wood zone have characteristic anatomical features
presenting a large amount of fibre with G layer and very thin S
2
layer (Fig. 4 A).

Clair G layer shrinkage 3
35°
Fig. 2: Recovery of the verticality of a poplar stem after the container have been
tilted 35°. Tension wood is produced on the upper side.
Fagus Sylvatica (L.)
A 150 years old tree was chosen after measurement of peripheral growth stresses at
breast height level on the standing tree, on eight positions around the trunk. This tree
was typical of a strongly dissymmetrical distribution of growth stresses (Fig. 3). A
high local level of growth stress is always related to presence of tension wood
(Trénard & Guéneau 1975; Sassus 1994). Wood sample were taken around the
highest values of growth stress (Z position on Fig. 3). In spite of large G layer in the
fibre cell wall, S
2
layer remains thicker than in poplar wood (Fig. 4 B).
0
50
100
150
200
250
0 45 90 135 180 225 270 315
angular position of trunk periphery (in degree)
DRLM (µm)
selected beech typical low stressed beech
II
I
Z
Fig. 3: Growth stress measurement on standing beech tree, on 8 angular positions of
trunk periphery. I: tree with regular low levels of growth stress, II: tree with a zone
(Z) of very high tensile growth stress.
Fig. 4: SEM observation of poplar (A) and beech (B) with gelatinous layer (G)
(also indicated S
2
layer) (Scale bar: 20 µm)
Tension
Wood
A
B
G
S
2

4 IAWA Journal,
Wood samples were stored in green condition before further processing into small
blocks or thin sections.
Massive blocks
Wood sticks (2 cm in longitudinal direction, section 5 x 5 mm²)
are cut up by splitting in order to guarantee a good axial direction. Sticks were then
cut to obtain 5 mm size cubes. Finally a last superficial planning is done manually
with a brand new razor blade in order to produce a nice transverse surface, the
sample being always kept in moist condition.
Thin sections
Transverse sections, 80 µm thick, were cut under water drop with a
microtome equipped with disposable razor blade. These sections were glued on the
edge with fibre direction parallel to support, in order to allow observations on
transverse sections on both sides of the sample.
Scanning electron microscopy
Massive blocks or thin sections are dehydrated with absolute ethanol, passed to
critical point and coated (300 Å of platinum) before observation. Thus, observations
are made in oven dry condition with a Cambridge S360 Scan Electron Microscope
(Fig. 5).
The tilting of receptor allows to obtain images of a same object for different view
angles.
Fig. 5: SEM images of poplar: A massive bloc, B thin section; scale bars: 100 µm.
Atomic force microscopy
Smaller massive blocks (500 x 500 x 500 µm
3
), prepared the same way as before,
are observed in their transversal section in water and in air-dry condition. Four states
are studied: green condition, green condition after 2 hours in 80°C water, air-dry
conditions, wet conditions after air-drying. Atomic Force Microscope (Dimension
3100, Nanoscope IIIa, Digital Instruments) was used to obtain topographic images
of a 50 x 50 µm² area (around 10 cells). The same cells are observed successively in
these conditions (Fig. 6).
A B

Citations
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TL;DR: This review presents a model of gelatinous-fibre organization and stresses the unique character of the gelatinous layer as a separate type of cell-wall layer, different from either primary or secondary wall layers.
Abstract: Gelatinous fibres are specialized fibres, distinguished by the presence of an inner, gelatinous cell-wall layer. In recent years, they have attracted increasing interest since their walls have a desirable chemical composition (low lignin, low pentosan, and high cellulose contents) for applications such as saccharification and biofuel production, and they have interesting mechanical properties, being capable of generating high tensional stress. However, the unique character of gelatinous layer has not yet been widely recognized. The first part of this review presents a model of gelatinous-fibre organization and stresses the unique character of the gelatinous layer as a separate type of cell-wall layer, different from either primary or secondary wall layers. The second part discusses major current models of tensional stress generation by these fibres and presents a novel unifying model based on recent advances in knowledge of gelatinous wall structure. Understanding this mechanism could potentially lead to novel biomimetic developments in material sciences.

197 citations


Cites background from "Shrinkage of the gelatinous layer o..."

  • ...Further, in atomic force microscopy analyses of cut surfaces of tension wood (kept under water to avoid drying effects) Clair and Thibault (2001) observed pronounced longitudinal shrinkage of the G-layer relative to S-layers, corresponding to a 4.7% strain, which is much greater than the recorded…...

    [...]

Journal ArticleDOI
TL;DR: Measurements show that mesoporosity is high in tension wood with a typical thick G-layer while it is much less with a thinner G- layer, sometimes no more than normal wood.
Abstract: The mechanism for tree orientation in angiosperms is based on the production of high tensile stress on the upper side of the inclined axis. In many species, the stress level is strongly related to the presence of a peculiar layer, called G-layer, in the fibre wall. The structure of G-layer has been recently described as a hydrogel thanks to N2 adsorption-desorption isotherms of supercritically dried samples showing a high mesoporosity (pores size from 2 to 50 nm). This led us to revisit the concept of G-layer that was until now only described from anatomical observation. Adsorption isotherms of both normal wood and tension wood have been measured on six tropical species. Measurements show that mesoporosity is high in tension wood with typical thick G-layer while it is much less with thinner G-layer, sometimes no more than normal wood. The mesoporosity of tension wood species without G-layer is as low as in normal wood. Not depending on the amount of pores, the pore sizes distribution are always centred around 6-12 nm. These results suggest that, among species producing fibres with G-layer, large structural differences of G-layer exist between species

196 citations


Cites methods from "Shrinkage of the gelatinous layer o..."

  • ...In previous research, the structure of the G-layer has been described as possessing gel-like characteristics: large shrinkage (Clair and Thibaut, 2001; Fang et al., 2007) and high rigidification during drying (Clair et al....

    [...]

  • ...In previous research, the structure of the G-layer has been described as possessing gel-like characteristics: large shrinkage (Clair and Thibaut, 2001; Fang et al., 2007) and high rigidification during drying (Clair et al., 2003)....

    [...]

Journal ArticleDOI
TL;DR: It is proposed that, during cellulose crystallization, a part of the xyloglucan is trapped inside the crystal, inducing longitudinal tensile stress within it; another part of it is accessible and present between the G-layer and the outer wall layers.

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Abstract: The institutionalized separation between form, structure and material, deeply embedded in modernist design theory, paralleled by a methodological partitioning between modeling, analysis and fabrication, resulted in geometric-driven form generation. Such prioritization of form over material was carried into the development and design logic of CAD. Today, under the imperatives and growing recognition of the failures and environmental liabilities of this approach, modern design culture is experiencing a shift to material aware design. Inspired by Nature’s strategies where form generation is driven by maximal performance with minimal resources through local material property variation, the research reviews, proposes and develops models and processes for a material-based approach in computationally enabled form-generation. Material-based Design Computation is developed and proposed as a set of computational strategies supporting the integration of form, material and structure by incorporating physical form-finding strategies with digital analysis and fabrication. In this approach, material precedes shape, and it is the structuring of material properties as a function of structural and environmental performance that generates design form. The thesis proposes a unique approach to computationally-enabled form-finding procedures, and experimentally investigates how such processes contribute to novel ways of creating, distributing and depositing material forms. Variable Property Design is investigated as a theoretical and technical framework by which to model, analyze and fabricate objects with graduated properties designed to correspond to multiple and continuously varied functional constraints. The following methods were developed as the enabling mechanisms of Material Computation: Tiling Behavior & Digital Anisotropy, Finite Element Synthesis, and Material Pixels. In order to implement this approach as a fabrication process, a novel fabrication technology, termed Variable Property Rapid Prototyping has been developed, designed and patented. Among the potential contributions is the achievement of a high degree of customization through material heterogeneity as compared to conventional design of components and assemblies. Experimental designs employing suggested theoretical and technical frameworks, methods and techniques are presented, discussed and demonstrated. They support product customization, rapid augmentation and variable property fabrication. Developed as approximations of natural formation processes, these design experiments demonstrate the contribution and the potential future of a new design and research field. Thesis Supervisor: William J. Mitchell Title: Alexander Dreyfoos Professor of Architecture and Media Arts and Sciences Department of Architecture, MIT

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Abstract: Summary • A cinnamoyl-CoA reductase 1 knockout mutant in Arabidopsis thaliana was investigated for the consequences of lignin synthesis perturbation on the assembly of the cell walls. • The mutant displayed a dwarf phenotype and a strong collapse of its xylem vessels corresponding to lower lignin content and a loss of lignin units of the noncondensed type. Transmission electron microscopy revealed that the transformation considerably impaired the capacity of interfascicular fibers and vascular bundles to complete the assembly of cellulose microfibrils in the S2 layer, the S1 layer remaining unaltered. Such disorder in cellulose was correlated with X-ray diffraction showing altered organization. • Semi-quantitative immunolabeling of lignins showed that the patterns of distribution were differentially affected in interfascicular fibers and vascular bundles, pointing to the importance of noncondensed lignin structures for the assembly of a coherent secondary wall. • The use of laser capture microdissection combined with the microanalysis of lignins and polysaccharides allowed these polymers to be characterized into specific cell types. Wild-type A. thaliana displayed a two-fold higher syringyl to guaiacyl ratio in interfascicular fibers compared with vascular bundles, whereas this difference was less marked in the cinnamoyl-CoA reductase 1 knockout mutant.

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Cites background from "Shrinkage of the gelatinous layer o..."

  • ...It is interesting to note that similar shrinkage of the gelatinous layer of fibers from tension wood, in which the lignin content is very low, also occurs in the same conditions of dehydration (Clair & Thibaut, 2001; Fig....

    [...]

References
More filters
Journal ArticleDOI
TL;DR: After considering both earlier evidence and the present results, it was concluded that the gelatinous layer has neither a honeycomb nor a homogeneous texture, as has been suggested, but that it consists of concentric lamellae of cellulose microfibrils.
Abstract: Pronounced tension wood from four North-American hardwood species has been examined by light and electron microscopy. Delignified fibers were also studied. The gelatinous layer was in all cases loosely attached to S2 but varied considerably in thickness within each species and was in one case terminated towards the lumen by a layer resembling S3. A terminal lamella was not observed. After considering both earlier evidence and the present results, it was concluded that the gelatinous layer has neither a honeycomb nor a homogeneous texture, as has been suggested, but that it consists of concentric lamellae of cellulose microfibrils. In the absence of hemicelluloses and lignin, the microfibrils are probably bound together less firmly than they are in other cell wall layers. The gelatinous layer is more readily separated from the remainder of the cell wall by mechanical forces than by chemical reagents.

82 citations

Journal ArticleDOI
TL;DR: Barber and Meylan as mentioned in this paper showed that wood shrinkage is intimately connected with the micro-fibril angle (the angle between the microfibrils in the 82 layer and the longitudinal axis of the cell).
Abstract: Introduction In a previous paper, Barber and Meylan (i) brought evidence to show that the amounts by which wood shrinks as it is dried is intimately connected with the microfibril angle (the angle between the microfibrils in the 82 layer and the longitudinal axis of the cell). The relation is not a simple one. Thus, shrinkage in length tends to be small, 0.2 per cent or less, if the microfibril angle is less than 20°, and may even be negative when the angle is near 30°, but becomes large and positive when the angle exceeds 40°. Thus, in a recent paper Meylan (6) reports longitudinal shrinkage exceeding 5 per cent when the microfibril angle is 50°; the longitudinal shrinkage then exceeds the transverse shrinkage. The longitudinal shrinkage, therefore, is by no means linearly proportional to the microfibril angle, though the two appear to be intimately related. Barber and Meylan (i) proposed a theoretical model to account for this connexion. The model is of course a highly idealised representation of a cell of wood, but since it succeeds in predicting many of the features of shrinkage it would seem useful as a guide to further study. The theoretical model pictures the wall of the wood cell as consisting of a matrix of amorphous substances that can lose water and consequently shrink in volume. In the absence of any constraint it is assumed that this material would show equal contractions in all directions. Embedded in the wall, however, are numerous long thin crystals of cellulose, the microfibrils, all lying approximately in the same direction. The theory supposes that these microfibrils would not tend to change in length as a result of loss of water. They therefore act as a constraint; when the matrix loses water and shrinks in volume, the microfibrils elastically resist any change in their length. Consequently the matrix material, as it shrinks in volume is deformed in shape to an extent that depends on the relative values of the rigidity of the matrix and the stiffness in extension of the microfibrils. The cell consequently shows different shrinkages in the longitudinal and transverse directions. This theory evidently attempts a macroscopic rather than a molecular view of the shrinking process. No attempt is made to say why the matrix should decrease in volume when it loses water, and the theory does not attempt to account for the well-known hysteresis of shrinkage by which the form of wood depends not only on its moisture content but also on its past history

76 citations


"Shrinkage of the gelatinous layer o..." refers background in this paper

  • ...One of the first models, which is still a reference, is the Barber and Meylan 's one (1964) refined by Barber (1968)....

    [...]

Journal ArticleDOI
TL;DR: In this paper, a relation describing the shrinkage properties of a fiber-composite is applied to a multilayered thin-walled model of wood, with the theory developed it is possible to specify shrinkage with respect to moisture content, as well as with factors involved in cell-wall geometry and composition.
Abstract: A relation describing the shrinkage properties of a fibre-composite is applied to a multilayered thin-walled model of wood. With the theory developed it is possible to specify shrinkage with respect to moisture content, as well as with factors involved in cell-wall geometry and composition. However, until more is known of the properties of the water-reactive matrix component of the composite it is only practicable to describe shrinkage with respect to the geometrical and compositional factors at the moisture-content of the stress free state.

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TL;DR: In this paper, a study on the shrinkage of wood representing the wide range of morphology variation in leaning trees was carried out on 13 trees of Eucalyptus regnans, one tree of Sieberi and four of Pinus radiata, and specimens taken at close intervals around the circumference of each stem.
Abstract: This is a study on the shrinkage of wood representing the wide range of morphology variation in leaning trees It involved 13 trees of Eucalyptus regnans, one of Eucalyptus sieberi and four of Pinus radiata, and specimens taken at close intervals around the circumference of each Data indicated a systematic modulation, between extremes at upper and lower sides of each stem, in longitudinal growth strains, relative proportions of thin, medium and thick-walled fibres, microfibril angle in the S2 layer of these, and both Klason and acid-soluble lignin content Analyses indicated that the microfibril angle in S2 was a prime factor in influencing both longitudinal and volumetric shrinkage reactions; proportion of thick-walled fibres in the tissue, thickness of S2 relative to S1, and variations in lignification also were involved Unusually thick-walled fibres were associated with visco-elastic strain recovery effects, which could form a substantial part of dimensional changes apparently attributable to shrinkage

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Journal ArticleDOI
TL;DR: In this paper, the reinforced-matrix hypothesis offered by Barber and Meylan (1964) was reformulated by using a multi-layered wood fiber model, and the formula describing the dynamical behavior of swelling and shrinking wood fiber was derived.
Abstract: The anisotropic mechanism of wood swelling and shrinkage was investigated theoretically. The reinforced-matrix hypothesis offered by Barber and Meylan (1964) was reformulated by using a multi-layered wood fiber model, and the formula describing the dynamical behavior of swelling and shrinking wood fiber was derived. For modelling, the moisture content changes were taken into consideration as an explicit parameter. It is expected to predict the anisotropic swelling and shrinking process of wood dynamically and quantitatively, as well as to initiate elucidating the interaction between the moisture and cell wall components on the basis of the present model. Some concrete calculations will be demonstrated in the following report, and the results will be compared with the experimental ones.

52 citations


"Shrinkage of the gelatinous layer o..." refers background in this paper

  • ...…other components properties (cellulose, hemicellulose and lignin), changes in matrix behaviour during drying and introducing the different cell wall layers have been proposed to refine this first theory (Barrett et al. 1972; Cave 1972b, 1978; Sassus 1998; Gril et al. 1999; Yamamoto 1999)....

    [...]