Effect of Reactive Gas Composition and Duty Cycle in Low-Pressure DC-Pulsed Plasmas on the Surface Oxidation of Nitrile Rubber.

Nitrile rubber (NBR) is widely used in components across several industrial sectors due to its properties that are suitable for engineering applications. Surface-environment interactions often limit performance, which depends critically on surface characteristics, especially barrier properties for sealing and membrane applications. This study investigates the effects of low-pressure direct-current pulsed plasma treatment in O2/Ar atmospheres on NBR surfaces to generate oxidized layers. Samples were treated at duty cycles of 30% and 70% with oxygen contents of 20% (low) and 80% (high). Nanoindentation post-treatment revealed increased surface contact stiffness, while differential scanning calorimetry (DSC) confirmed unchanged bulk properties. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy indicated the incorporation of oxidized groups and reduced C-H signals. The highest duty cycles (70%) improved sputtering species production, and the highest oxygen content (80%) enhanced O ion creation and surface oxidation, as evidenced by optical emission spectroscopy (OES) and X-ray photoelectron spectroscopy (XPS). XPS depth profiling showed a rising oxidation profile (oxygen implantation) at the treated surface. Based on a plasma-surface interaction mechanism, the condition with 80% oxygen and 30% duty cycle yields the highest surface oxidation level. It potentially enhances barrier properties, contributing to plasma-parameter optimization for tailored NBR surface modifications.