Influence of water on the mechanical properties of wood investigated using X-ray and neutron scattering
The influence of water on the mechanical properties of wood has been investigated in situ using X-ray microdiffraction on tangential cuts and single fibres of pine earlywood. Simultaneously, the orientation and elongation of the cellulose crystallites inside the composite material has been monitored during tensile stretching experiments. The softening in the beginning of the macroscopic stress-strain curve of the samples with a moisture content above the fibre saturation point has been localised in the matrix surrounding the microfibrils, lining up along the direction of the external tension force. Interestingly, the strain-hardening close to rupture has been independent on water content, possibly due to the strong bonds, apparently unaffected by the water molecules, along the polymer chains. Additionally, the local dynamics of a flax fibre bundle in wet and dry state have been studied by means of inelastic neutron scattering showing a clear anisotropy for motions between 2 and 7 meV at 300 and 180 K originating from the changes in the less ordered regions accessible for water.