Unsaturated polyester composites reinforced with flax fibers: effect of cold plasma and autoclave treatments on mechanical and permeation properties

In composite materials, fibers used as reinforcements are usually synthetic fibers such as glass. Since several years, for economic and environmental reasons, there has been an increasing interest in using plant fibers in composite systems. In this work, polyester composites reinforced by flax fibers submitted to helium cold plasma and/or autoclave treatments were investigated by means of water permeation measurements and mechanical tests. The analysis of the permeation and mechanical results has shown that plasma treatment improves fiber/matrix adhesion while autoclave treatment reduces water solubility in the fibers. For reinforced composites, therefore, autoclave treatment is more efficient in terms of water permeability and plasma treatment gives better stiffness in terms of mechanical properties. However, autoclave treatment followed by plasma treatment on flax fibers is recommended to obtain a good compromise for increasing both moisture resistance and stiffness of reinforced composites.