Résumé
Over the past decades, a tremendous interest has been developed concerning plant fibre used to reinforce composite materials as these fibers show comparable mechanical properties and higher ecological benefits than synthetic fibres such as glass fibres. Environmental concerns are currently driving interest in the replacement of thermoset matrices by thermoplastic polymers and pave the way for recycling and composting as end-of-life routes for plant fibre composites. However, using thermoplastic polymers as a matrix involves long processing cycles at high temperature, which may negatively affect both structure and mechanical properties of plant fibres. In this work, structural evolution and mechanical behaviour of flax fibre cell walls were dynamically monitored in-situ by X-ray diffraction and nanoindentation from ambient to 230°C. A drop in local mechanical performance of flax cell walls, associated with structural evolution at different scales and changesin the biochemical composition, were noticed while increasing temperature. This work, proposing for the first time an in-situ investigation of the dynamic evolution in temperature of the flax cell wall properties, also highlighted the reversible behaviour of their crystalline structure and local mechanical properties, after cooling to room temperature