Surface Analysis of Polymers Treated by Remote Atmospheric Pressure Plasma

The surfaces of high-density polyethylene (HDPE), poly(methyl methacrylate) (PMMA), and polyethersulfone (PES) were treated with a low-temperature, atmospheric pressure oxygen and helium plasma. The polymers were exposed to the downstream afterglow of the plasma, which contained primarily oxygen atoms and metastable oxygen molecules (1Δg O2), and no ions or electrons. X-ray photoelectron spectroscopy (XPS) of HDPE revealed that 20% of the carbon atoms were converted into oxidized functional groups, with about half of these being carboxylic acids. Attenuated total reflection infrared spectroscopy of all three polymers was obtained in order to determine the types of functional groups formed by atmospheric plasma exposure. It was found that the polymers were rapidly oxidized with addition of alcohols, ketones, and carboxylic acids to the carbon backbone. Chain scission occurred on HDPE and PMMA, while on PES the aromatic groups underwent ring-opening and insertion of carboxylic acid.