(378a) Mechanism for Surface Activation of Aromatic Polymers with Atmospheric Pressure Plasmas

An atmospheric pressure oxygen and helium plasma was used to treat the surfaces of polyetheretherketone, polyphenylsulfone, polyethersulfone, and polysulfone. These aromatic polymers were exposed to the afterglow of the plasma, which contained oxygen atoms, and to a lesser extent metastable oxygen (¹D_g O₂) and ozone, for periods of time ranging from 0 to 2.5 seconds. All the materials were converted from a hydrophobic state with an initial water contact angle of 85±5° to a hydrophilic state with a final water contact angle of 13±2°. It was found that this surface treatment increased the bond strength to several different adhesives by as much as 4 times. Analysis of the surface composition by x-ray photoelectron spectroscopy revealed that plasma treatment oxidized between 7% and 27% of the aromatic carbon atoms on the polymer surfaces, and converted them into aldehyde and carboxylic acid groups. The most dramatic effect was evidenced by polyetheretherketone, where the amount of surface carbon attributable to carbonyl (ketone and aldehyde) and carboxylic acid groups increased from 5% to 11% and from 0% to 19%, respectively. It was concluded that the oxygen atoms generated by the atmospheric pressure plasma insert into the double bonds on the aromatic rings, forming a 3-member epoxy ring, which subsequently undergoes ring opening, and further oxidation to yield an aldehyde on one end of the 6-C-atom-chain and a carboxylic acid on the other end of the chain. The experimental results as well as a detailed description of the reaction mechanism will be presented at the meeting.