Chemical characterization of bulk steel-bulk fluoropolymer interfaces

Understanding the parameters that influence the strength of the interfacial adhesion between a metal and a polymer is of extreme importance for many industrial applications. It has been observed that the mechanical behavior of steel/fluoropolymer (S/F) interfaces is highly dependent on the chemistry of the interface. In this work, the chemical composition of a S/F interface is studied in an attempt to understand the relationship between the steel and the fluoropolymer and it's affect on the bond strength. Since the actual interface is quite thin, new sample preparation techniques were developed to expose the interface without introducing artifacts. Using these sample preparation techniques detailed morphological studies of the interface were performed using Scanning Electron Microscopy (SEM), which showed that the S/F interface exhibits significant roughness that may enable mechanical anchoring to occur in the interface. To determine the chemical composition of the interface, and the binding states of fluorine and carbon across the interface, Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS) characterization techniques were used, respectively. Both SEM and AES indicated the presence of an oxide layer on the metal of approximately 200 nm. Additionally, XPS revealed the presence of metal fluorides at the interface, and suggested that both metal fluoride formation and the metal oxide layer are necessary for a strong S/F bond, however more studies are required to completely understand the effect of metal oxides and metal fluorides on bond strength.