ADHESION OF CRYSTALLINE POLYPHENYLETHERETHERKETONE (PEEK) IN METAL-TO-METAL JOINTS

The characteristics of melt-crystallized polyphenyletheretherketone (P EEK) as an adhesive for steel-to-steel joints have been investigated. Interfacial chemistry, which plays an important role in determining wh ether adhesion will be poor or good at PEEK/steel interfaces, involved the following reactions. Oxygen-catalysed deformation of PEEK in air led to a low rate of crystallinity, which gave poor adhesion to the st eel surfaces. The enrichment of Fe2O3 by extensive oxidation of the in terfaces also created an undesirable boundary region, thereby indicati ng that failure occurs cohesively through this weak Fe2O3 layer. X-ray photoelectron spectroscopy (XPS) data suggest that there is no chemic al interaction of well-crystallized PEEK with Fe2O3 at the top surface of steels. In contrast, in nitrogen, interfacial Fe- and Cr-O-C compl exes, formed by a charge transfer between elemental Fe or Cr in steel and oxygen in the ketone groups (C = O) of crystallized PEEK, contribu ted significantly to strengthening the PEEK-to-steel bonds.