The Anisotropic Shrinkage of Wood. A Theoretical Model

Barber, N. F.; Meylan, B. A.

doi:10.1515/hfsg.1964.18.5.146

Cited by 120 publications

(55 citation statements)

References 6 publications

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“…Afterward, Okuyama and his associates accumulated experimental data that positively demonstrated Wilson's suggestion. They developed a more sophisticated theory, called ''unified hypothesis'' [79,80], that incorporated the reinforced matrix mechanism originally proposed by Barber and Meylan [81]. It was later formulated by Yamamoto and coworkers, who applied the reinforced matrix theory to multi-layered cylinders as homogenized models of xylem fibers [82], i.e., softwood tracheid or hardwood normal fiber (CML ?…”

Section: The Unified Hypothesismentioning

confidence: 99%

Tree growth stress and related problems

et al. 2017

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Tree growth stress, resulted from the combined effects of dead weight increase and cell wall maturation in the growing trees, fulfills biomechanical functions by enhancing the strength of growing stems and by controlling their growth orientation. Its value after new wood formation, named maturation stress, can be determined by measuring the instantaneously released strain at stem periphery. Exceptional levels of longitudinal stress are reached in reaction wood, in the form of compression in gymnosperms or higher-than-usual tension in angiosperms, inspiring theories to explain the generation process of the maturation stress at the level of wood fiber: the synergistic action of compressive stress generated in the amorphous ligninhemicellulose matrix and tensile stress due to the shortening of the crystalline cellulosic framework is a possible driving force. Besides the elastic component, growth stress bears viscoelastic components that are locked in the matured cell wall. Delayed recovery of locked-in components is triggered by increasing temperature under high moisture content: the rheological analysis of this hygrothermal recovery offers the possibility to gain information on the mechanical conditions during wood formation. After tree felling, the presence of residual stress often causes processing defects during logging and lumbering, thus reducing the final yield of harvested resources. In the near future, we expect to develop plantation forests and utilize more wood as industrial resources; in that case, we need to respond to their large growth stress. Thermal treatment is one of the possible countermeasures: green wood heating involves the hygrothermal recovery of viscoelastic locked-in growth strains and tends to counteract the effect of subsequent drying. Methods such as smoke drying of logs are proposed to increase the processing yield at a reasonable cost.

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Section: The Unified Hypothesismentioning

confidence: 99%

Tree growth stress and related problems

et al. 2017

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“…in longitudinal direction [18], by 1.9-3.3% in the transverse direction, by 2.3-3.2% in the longitudinal direction, by 14.5-18.2% in area and by 12.4-17.3% in height in humidity cycles of 50-78-21% [13]. Apart from the arrangement of the polymers, another explanation for the anisotropic swelling of fibers was the ''reinforced matrix hypothesis'' [71,177,178]. In this hypothesis, the lignin-hemicellulosic matrix is assumed to shrink isotropically and to work like a skeleton in the secondary wall, whereas the cellulose microfibrils are assumed not to shrink during desorption.…”

Section: Single Fiber Hygroexpansionmentioning

confidence: 99%

Factors affecting the hygroexpansion of paper

Lindner

2017

J Mater Sci

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Paper is a widely used packaging material and is nowadays regaining importance, e.g., as bio-based and biodegradable material. Moreover, new technologies such as polymer-fiber composites, printed electronics and the deep drawing of paper are developing. The process stability and also the resulting quality of paper converting processes such as coating, metallization, printing, and the printing of electronics are highly affected by the hygroexpansion of paper. In order to reduce production instability and to choose and develop paper substrates with ideal characteristics, critical parameters need to be known. This paper offers an extensive overview of those parameters, starting at a molecular and microscopic level with the effect of the constituents and morphology of single fibers, before moving on to paper contents, chemical modifications and additives and finally concluding with paper production and fiber network modification. It was found that the major influences are single fiber sorption, inter-fiber contacts, microfibril angle, fiber morphology (length, width, curliness) and fiber orientation. This review gives new ideas and insights for technologists working in research, development and production optimization of paper-based products.

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“…En revanche, la mise en évidence sur les grandis élagués à 50 % de retraits négatifs (donc d'expansion du bois lorsque le taux d'humidité diminue) ne doit pas surprendre outre mesure car le phénomène a déjà été mentionné pour d'autres espèces (Anonyme, 1960-HANN, 1969; BARBER et MEYLAN (1964) ont même prouvé mathématiquement, en partant d'un modèle théorique, que de tels retraits négatifs pouvaient se produire lorsque, à un angle important d'insertion des microfibrilles sur l'axe de fibres, s'ajoute un rapport élevé entre les modules d'élasticité de la partie cristalline et de la partie amorphe de la couche moyenne de la membrane secondaire; lorsque la zone non cristalline a une forte teneur en eau, son module d'élasticité est faible et, par suite, le rapport précité croît, entraînant la possibilité de retraits négatifs; l'observation faite sur les arbres élagués concorde assez bien avec cette théorie, puisqu'on peut admettre que l'enlèveront d'une partie importante de la couronne vivante a pour effet de réduire l'évapo-transpiration, donc d'augmenter la teneur en eau du bois.…”

Section: -Commentairesunclassified

Influence de l'élagage de branches vivantes sur la structure des accroissements annuels et sur quelques caractéristiques du bois de Douglas et de Grandis

Polge¹,

Keller²,

Thiercelin³

1973

Ann. Sci. forest.

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RÉSUMÉUn élagage sévère a pour effet de réduire la progressivité du passage du bois initial au bois final et d'augmenter la densité moyenne, la densité maximale annuelle, la densité minimale annuelle, ainsi que le nombre et l'ampleur des doubles cernes.La rétractibilité est accrue dans le sens tangentiel et dans le sens radial, mais légèrement diminuée dans le sens longitudinal.D'une façon générale, pour un même taux d'élagage, les effets sont plus marqués sur le Grandis que sur le Douglas.

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The Anisotropic Shrinkage of Wood. A Theoretical Model

Cited by 120 publications

References 6 publications

Tree growth stress and related problems

Tree growth stress and related problems

Factors affecting the hygroexpansion of paper

Influence de l'élagage de branches vivantes sur la structure des accroissements annuels et sur quelques caractéristiques du bois de Douglas et de Grandis

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