Résumé
This chapter aims to illustrate the correlation in the effect of free surface energy modification of natural fibers on the mechanical behavior of bio-based composites. It has been proved that enhancing the wettability of flax fibers by liquid epoxy resin implies a lower porosity amount in composites. The main outcome of multiscale consideration is that even if elementary fibers and yarns are embrittled and interface properties at the microscale are lowered by a thermal or chemical surface energy modification, the mechanical behavior of composites manufactured by liquid composite molding can be improved. Some questions are still open on the methodology to optimize treatments, especially on the scale at which the treatment is applied (yarn or fabric). The extension of those considerations to biocomposites with thermoplastic matrices should be done in the upcoming years to manufacture sustainable and circular composites.