The effect of the G-Layer on the viscoelastic properties of tropical hardwoods

John Paul Mc Lean (1) , Olivier Arnould (1) , Jacques Beauchêne (2) , Bruno Clair (1)

1 MAB - Mécanique de l'Arbre et du Bois
2 ECOFOG - Ecologie des forêts de Guyane

Context and aim : This study aimed to examine the effect of the tension wood G‐layer on the viscoelastic properties of wood. Methods : 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 Glayer, whilst the tension wood from the latter three had no Glayer. 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. Results : 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. Conclusion : 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.

Mots clés: G‐layer . Reaction wood . Tropical wood . Viscoelasticity

Domaines: Biomécanique [physics.med-ph]; Biomécanique [physics.med-ph]; Mécanique des matériaux [physics.class-ph]; Mécanique des matériaux [physics.class-ph]; Mécanique des structures [physics.class-ph]; Mécanique des structures [physics.class-ph]

John Paul Mc Lean, Olivier Arnould, Jacques Beauchêne, Bruno Clair. The effect of the G-Layer on the viscoelastic properties of tropical hardwoods. Annals of Forest Science, 2012, 69 (3), pp.399-408. ⟨10.1007/s13595-011-0164-1⟩. ⟨hal-00677460⟩