Effect of low‐pressure plasma processing parameters on the surface topography of a CF/PEEK composite for adhesive bonding

Abstract In recent decades, thermoplastic matrix fiber composites have become attractive for many modern aerospace structural applications. However, their adhesive bonding remains challenging, so it is essential to study surface pre‐treatments to improve their potential for adhesive bonding. In this study, an aerospace‐grade carbon fiber reinforced poly ether ether ketone composite, which was adhesively bonded with a structural epoxy‐film adhesive, has been investigated. The composite adherends were pre‐treated using low‐pressure oxygen plasma across a range of processing parameters. The treated surfaces were analyzed using scanning electron microscopy, X‐ray photoelectron spectroscopy, and contact angle analysis to characterize the surface topography, chemistry, and wettability of the composite after the different levels of treatment. A plasma treatment power of 180 W for a duration of 5 min was shown to provide the best results in surface characterization and single‐lap‐shear joint testing. Compared to the traditional thermosetting composites, a lower power or/and shorter duration of the plasma treatment was sufficient to achieve good adhesion for the thermoplastic composites. A nano‐etching effect induced by relatively long treatment times was observed, which contributed to the formation of nano‐grooves on the surface of the adherends without exposing fibers on the surfaces. Highlights A plasma treatment improves the adhesive performance of the CF/PEEK composite. Better adhesion is due to enhanced surface activation and nano‐etching. The optimized parameter for better SLS strength is 180 W for 5 min. A lower power or shorter duration of PL is sufficient for TPCs than TSCs.