SF6 Plasma Surface Modification of Flax Fibers for Improved Adhesion in Polypropylene Composites

Flax fibers have attracted growing interest in the automotive industry as an eco-friendly reinforcement for polymer composites. However, their limited interfacial compatibility with hydrophobic matrices is detrimental to adhesion, a key factor in the composite mechanical behavior. To address this issue, this study investigates the surface modification of flax fibers using sulfur hexafluoride (SF<inf>6</inf>) plasma. The proposed treatment promotes fiber surface hydrophobization while preserving their bulk properties. The effect of SF<inf>6</inf> plasma treatments on flax fiber adhesion to polypropylene (PP) blends containing post-consumer material is thoroughly examined. The analysis, conducted using scanning electron microscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, and infrared spectroscopy, reveals that the plasma treatment induces the etching of amorphous substances present in the fibers, including amorphous cellulose, hemicelluloses, and lignin. Plasma etching in combination with fluorination significantly enhances the adhesion of flax fibers to the PP blend matrix. Notably, the treated fibers exhibit improvements in tensile strength (9%) and elastic modulus (25%) compared to untreated fibers. These findings highlight the potential of SF<inf>6</inf> plasmas as an effective pretreatment method for natural fiber composite reinforcements.