Enhancing Surface Activation in Unidirectional Carbon Fiber/Epoxy Composites through Low-Temperature Plasma

The physicochemical characteristics of carbon fiber reinforced polymer (CFRP) surfaces are critical for structural bonding. Achieving optimal adhesion remains challenging, as conventional treatments often involve aggressive chemicals or toxic residues. Plasma treatments offer an environmentally friendly alternative, inducing surface modifications such as increased roughness, enhanced hydrophilicity, incorporation of high-energy functional groups, and reactive sites formation. This study investigates argon, nitrogen, and oxygen plasma treatments on unidirectional carbon fiber/epoxy composites (CYCOM 5320-1) at varying power (20 and 50 W) and durations (600, 1200, 1800 s) to evaluate effects on surface activation, hydrophobic recovery, temporal stability, and bulk viscoelastic properties. Results show plasma effectively cleans and decontaminates surfaces while improving roughness and wettability. Argon plasma at low power and short duration increased roughness by ∼ 17% and enhanced existing functional groups. Nitrogen plasma at low power and longer durations increased roughness by 140% and introduced nitrogen-rich groups, improving wettability. Oxygen plasma produced the most substantial effects even at low power, with ∼200% roughness increase and incorporation of highly energetic oxygen-containing groups, favorable for structural adhesion. FTIR, XPS, SEM, and DMA analyses supported these findings, providing detailed insights into surface activation mechanisms.