Optimization of interfacial adhesion and mechanical performance of flax fiber-based eco-composites through fiber fluorination treatment

Abstract

Natural fibers, such as flax, are more and more used as biobased reinforcement for eco-composites manufacturing but their natural polarity makes them incompatible with most polymers (mostly dispersive). Nowadays, treatments such as torrefaction are known to reduce the polarity of natural fibers and thus increase the mechanical performance of the reinforced composites. However, these treatments could harm fibers and limit the gain in performance. Thereby, the use of a controlled fluorination treatment allowed, via the grafting of fluorine on the fiber surface, to decrease the polarity of these fibers while maintaining an equivalent Young's modulus and limiting the reduction of at break performance to just ∼30 %. Therefore, by incorporating these fluorinated reinforcements in an epoxy matrix and by mechanically testing these composites, not only superior mechanical performances to those reinforced by raw fibers, but also superior to torrefied fiber-reinforced composites were measured, e.g.: the flexural modulus increased by 25 % after fluorination vs. 10 % after torrefaction and the flexural strain at break was enhanced by 10 % after fluorination vs. decrease by 35 % after torrefaction).