Improving the properties of UD flax fibre reinforced composites by applying an alkaline fibre treatment

Present-day industry takes an interest in environment friendly materials, due to economic and ecological reasons. The use of natural materials in composite parts fits well into this picture: plant fibres that reinforce polymer matrices can replace glass fibres in many cases, although applications are often limited to non-structural parts. The poor interface in a non-treated natural fibre reinforced composite prevents the parts to be used to their full capacity. Consequently, this study concentrates on a simple but effective fibre treatment (i.e. alkalisation) that will enable a better adhesion between flax fibres and epoxy matrix. Parameters such as time and concentration are being optimised, in order to develop a continuous process for the treatment and resin impregnation of unidirectional flax fibre epoxy composites. This paper shows a clear improvement of the mechanical properties of the resulting material: e.g. a mild treatment in a 4% NaOH solution for 45 s will increase the transverse composite strength up to 30%.