The effect of the G‐layer on the viscoelastic properties of tropical hardwoods
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Context and aim
This study aimed to examine the effect of the tension wood G‐layer on the viscoelastic properties of wood.
Tension wood and opposite wood samples were obtained from six French Guianese tropical rainforest species (Sextonia rubra, Ocotea guyanensis, Inga alba, Tachigali melinoni, Iyranthera sagotiana and Virola michelii); the tension wood of the former three of these species had a G‐layer, whilst the tension wood from the latter three had no G‐layer. Tensile dynamic mechanical analysis (DMA) was performed on green never dried wood samples in the longitudinal direction with samples submerged in a water bath at a temperature (30°C) and frequency (1 Hz) representative of the conditions experienced by wood within a living tree. Then, DMA was repeated with samples conditioned to an air-dried state. Finally, samples were oven-dried to measure longitudinal shrinkage.
Tension wood did not always have a higher longitudinal storage (elastic) modulus than opposite wood from the same tree regardless of the presence or absence of a G‐layer. For the species containing a G‐layer, tension wood had a higher damping coefficient and experienced a greater longitudinal shrinkage upon drying than opposite wood from the same species. No difference was found in damping coefficients between tension wood and opposite wood for the species that had no G‐layer.
It is proposed that the different molecular composition of the G-layer matrix has an influence on the viscoelasticity of wood, even if a biomechanical gain is not yet clear. This study shows that rheological properties and longitudinal shrinkage can be used to detect the presence of a G‐layer in tension wood.
KeywordsDMA G‐layer Reaction wood Tropical wood Viscoelasticity
This project was supported by the French National Research Agency (ANR05 BDIV 012 04–WOODIVERSITY) and a joint project JSPS-CNRS. We thank Professor Yamamoto, K. Abe and J. Ruelle (Nagoya University, Japan) for help in field measurements and sample collection; Soepe Koese for sample preparation at the CIRAD facility in Kourou (French Guyana); and Professor Philip Harris (University of Auckland, New Zealand) for discussions about cell wall compositions. Finally, Gilles Camp from LMGC, University of Montpellier 2, is gratefully acknowledged for building the water bath and other necessary additions to the DMA apparatus.
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