Carbon fibres treatment by atmospheric cold plasma: A green opportunity for their functionalization

• Atmospheric cold plasma activates both CF and sizing. • Air-generated plasma gradually modifies CF surface towards hydrophilicity. • Nitrogen-generated plasma quickly induces super-hydrophilicity. Carbon fibres (CFs) are considered as one of the most important components in composite materials. Their lightweight and mechanical properties make them suitable for obtaining high-quality reinforced composites. Moreover, when a composite material is designed, the best interaction fibre-hosting matrix needs to be pursued. CFs, on the other hand, suffer from poor surface reactivity due to the lack of reactive functional groups and need to be functionalized and adequately protected from mechanical stresses by adding a protecting sizing layer. The present work investigates the innovative application of atmospheric cold plasma generated in air or in nitrogen for the direct systems (CF and sizing) functionalization with polar groups. The use of plasmas does not require additional chemical reactants and appears as a sustainable and green procedure. The surface functionalization, as well as the partial sizing removal, are demonstrated by several complementary analytical techniques (IR, TGA, XPS, SEM, AFM, and wettability WCA tests) on differently treated samples. The obtained outcomes appear without similar comparison in literature. It is proved the achievement of the polar oxygen- and nitrogen containing functional group’s introduction as well as the full water wettability obtained in 20 minutes of air plasma or in only 1 minute of nitrogen plasma treatment, without any evident damage of the substrates. The effectiveness of nitrogen-plasma in a very low exposure time and the graduality of the air-plasma treatments can be properly exploited for the environmentally friendly CFs functionalization without additional chemical reactants.