Enhancing mechanical properties and moisture durability of flax/polypropylene composite by plasma treatments

This work aims to enhance the mechanical properties and moisture durability of flax fiber-reinforced polypropylene composite by plasma treatments. Atmospheric pressure plasma activation, and plasma coating deposition using a hexamethyldisiloxane (HMDSO) monomer with pure N2 and a gas mixture of nitrogen (N2) and oxygen (O2) as carrier gas, were employed to modify the fiber surface in an open reactor. The surface properties were examined in terms of surface morphology, surface energy, and chemical composition. Flexural tests and moisture sorption tests were used to measure the mechanical properties and moisture absorption of the composites. Both N2 plasma activation and HMDSO-based plasma polymerization effectively enhanced the mechanical properties of the composites, attributed to increased surface roughness and improved chemical compatibility, respectively. The best mechanical performance was achieved with the HMDSO coating using pure N2 as the carrier gas, resulting in a 24% and 33% improvement in flexural strength and modulus at standard indoor humidity, respectively. While the HMDSO coating obtained with a 4.5% O2 admixture was less effective in enhancing the mechanical properties, it exhibited superior water resistance.Highlights Plasma treatments in an open reactor for natural fibers were explored. Exposure time of 90 s and power of 300 W is the optimal treatment parameter. Plasma coating with hexamethyldisiloxane enhanced the mechanical properties. Plasma coating with a silica-like structure enhanced the water resistance.