Ring Opening of Aromatic Polymers by Remote Atmospheric-Pressure Plasma

An atmospheric-pressure oxygen and helium plasma was used to treat the surfaces of polyetheretherketone, polyphenylsulfone, polyethersulfone, and polysulfone. Water-contact-angle measurements, mechanical pull tests, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy were used to analyze the change in polymer properties. Plasma treatment converted all the materials from a hydrophobic to a hydrophilic state in a few tenths of a second. The adhesive bond strength was increased from 1.1 to 3.8 plusmn 1.0 MPa for polyetheretherketone and from 0.6 to 1.3 plusmn 0.2 MPa for polyphenylsulfone. XPS revealed that plasma treatment oxidizes between 7% and 27% of the aromatic carbon atoms on the polymer surfaces and converts them into aldehyde and carboxylic acid groups. The degree of oxidation was highest for polyetheretherketone, where the fraction of surface carbon atoms attributable to carbonyl (ketone and aldehyde) and carboxylic acid groups increased from 5% to 11% and from 0% to 19%, respectively. It is concluded that the O atoms generated in the atmospheric-pressure plasma oxidize and open the aromatic rings available on the polymer chains and that this is responsible for the increased adhesion.