Thermo-compression forming of flax fibre-reinforced polyamide 6 composites: influence of the fibre thermal degradation on mechanical properties

The thermal degradation of plant-based fibres at high temperature is a main issue when manufacturing vegetal fibres/thermoplastic composites due to the high melting point of engineering polymers such as polyamide 6 (PA6). This paper aims at investigating the influence of the thermo-compression forming process parameters, such as the temperature and consolidation time, on the mechanical properties of continuous flax fibre-reinforced PA6 composites. Woven fabric flax/PA6 composites were prepared by compression moulding using a film-stacking process under different consolidation conditions according to a two-factor Doehlert design of experiments. Tensile and flexural properties were assessed. A second-order polynome was used to correlate the processing parameters and the mechanical properties (i.e. stiffness, strength and strain at break). Fracture mode changes with the consolidation conditions. The weakening of the fibres and eventually of the composite performances was ascribed to the increase in flax fibre thermal degradation.