Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Wood has a hierarchical structure involving several levels of organisation. The stiffness of wood relies on its capacity to transfer mechanical stress to its stiffest element at the lowest scale, namely crystalline cellulose. This study aims at quantifying to what extend crystalline cellulose contributes to wood stiffness depending on its moisture content. The crystal strains of cellulose were measured using X-ray diffraction on wet and dry specimens of spruce, based on a previously published methodology. The comparison between crystal strain and macroscopic strain shows that, during elastic loading, cellulose strain is lower than macroscopic strain. The means ratio of crystal/macroscopic strain amounts 0.85 for dry specimens and 0.64 for wet specimens. This strain ratio cannot be explained just by the projection effect due to the difference in orientation between cellulose microfibrils and cell wall, but results from deformation mechanisms in series with cellulose. Analysis shows that this series contribution represents a non-negligible contribution to wood compliance and is strongly moisture-dependent. This contribution amounts 9% for dry specimens and 33% for wet specimens, corresponding to a 4-fold increase in compliance for the series contribution. The origin of these strains is ascribed to mechanisms involving bending or shear strain at different scales, due to the fact that reinforcing element are neither perfectly straight nor infinitely long.
ISSN: 0266-3538

hal-01425031
https://hal.archives-ouvertes.fr/hal-01425031
https://hal.archives-ouvertes.fr/hal-01425031/document
https://hal.archives-ouvertes.fr/hal-01425031/file/Art_Almeras_al_Contribution_cellulose_moisture-dependent_elastic_behavior_2017.pdf
DOI : 10.1016/j.compscitech.2016.11.025

Éditeur(s) : HAL CCSD
Résumé : International audience
The hierarchical architecture of biopolymers induces remarkable behaviour. Wood mechanical properties mainly originate from the organization of wood tissue and interactions of cellwall components. The respective contribution on components inside those networks occurs at nanometric scale and still challenging to investigate in-situ. X-ray scattering techniques are now used as a routine technique to investigate internal organization of material components. For that purpose large-scale synchrotron facilities like ESRF offer leading X-ray sources capabilities (large energy range, high brilliance, high intensity, dedicated setups). ESRF's ID13 beamline serves high spacial resolution scanning setups to expertise in elastic scattering of monochromatic X-rays. Since analytical description of the scattering signal of cellulose have been well describe wood material benefit wide range of exposure conditions and sample environment. During this conference, we will present our achievements based on transverse sections of poplar specimens exposed to micrometric beam (1.2 μm side, 12.6 keV energy) to reveal crystalline cellulose distribution within wood tissue and to nanometric beam (100 nm side, 12 6 keV energy) to map the evolution of cellulose orientation within double cell wall over combined Wide-Angle (WAXS) and Small-Angle (SAXS) X-ray Scattering configuration. Within those setups hygrometric sample environment and stretching solicitations will be approached based on-going developments.
COST FP0802 Workshop 'Micro Characterisation of Wood Material'
Edimbourg, United Kingdom

hal-01113298
https://hal.archives-ouvertes.fr/hal-01113298