Mechanical properties of cellulose fibres and wood.: Orientational aspects in situ investigated with synchrotron radiation

Highly oriented native cellulose fibres ( flax) and softwood ( pine) have been investigated by means of X- ray diffraction. Local structural information was obtained by using X- ray microbeams. Tensile tests were performed in situ, revealing a change of orientation of cellulose microfibrils in materials with tensile strain. In flax fibres, the microfibrils rotate during the first percent of stretching, into a more parallel orientation with respect to the fibre axis. For wood, a decrease of orientation with the onset of strain hardening is found for the first time.