Kyoko Shimizu, Kristoffer Malmos, Susie-Ann Spiegelhauer, Jens Hinke, Allan Hjarbæk Holm, Steen Uttrup Pedersen, Kim Daasbjerg, Mogens Hinge
In this work, a number of diazonium tetrafluroborates, i.e. 4-nitrobenzene (NB), 4-benzoylbenzene (BP), benzene, and 4-(2-aminoethyl)benzene (AEB) diazonium salts, were electrografted and applied as primers on stainless steel (SS) surfaces to test the resulting bond strength and durability of a polyetheretherketone (PEEK) coating. Lap shear test was used to assess both initial adhesion of PEEK to SS with and without primer, and the durability of these joints after immersion in boiling water. Subsequently, the loci of failure were determined by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) analyses. Of the four primers investigated, only the NB gave improved initial strength as well as higher durability of the coating after boiling water treatment. In general, a strongly diminishing effect on the adhesion strength due to water penetration along the PEEK/SS interface followed by corrosion of the metal surface was found.
Failure modes of the coated samples varied for the NB primer from cohesive failure close to the PEEK/primer interface under dry condition, to partly interfacial failure at the primer/SS interface after immersion into the boiling water for 5 h, while complete interfacial failure was found in the BP and the AEB primer cases.