Mechanical analysis of elementary flax fibre tensile properties after different thermal cycles

Knowledge of the mechanical properties of biocomposite components, especially flax fibres, is of great interest for understanding reinforcement mechanisms. The aim of this work is to study the mechanical behaviour of flax fibres after different thermal treatments, representative of three thermoplastic composites process temperatures. Firstly, a specific analysis was conducted to identify the three different types of mechanical behaviours and study the fibre performances according to the thermal treatments. Secondly, the microfibrillar realignment process was carefully studied thanks to an analysis of the tangent Young's modulus - strain curves and of the stress at different phases of the loading. Then, to better understand the influence of the temperature, TGA experiments were carried out on flax fibres after the thermal cycles. We highlighted a significant decrease of the mechanical performances at 250 °C which could be explained by some evolutions of their mechanical behaviour induced by structural modifications of the cell walls.