Friction induced mechanochemical and mechanophysical changes in high performance semicrystalline polymer

By using X-ray photoelectron spectroscopy (XPS) and Fourier transform Raman (FT-Raman) spectroscopy, the worn specimens of polyetheretherketone (PEEK) tested under unlubricated sliding friction and wear conditions at a consta nt sliding speed were investigated in order to reveal mechanochemically and mechanophysically induced structural changes of polymer as well as wear me chanisms on a molecular scale. Chain scission was found on the worn surface layer. The results suggest that oxidation was the major mechanochemical re action that followed the chain scission on the top surface. Evidence for ch ain branching or even crosslinking in bulk materials was also presented. Mo reover, two-stage loading dependencies were found for both surface and subs urface in the bulk as revealed through wear rate measurement and wear debri s analysis. It was proved that a thermo-activation of polymer segments may be responsible for the transition in the dependence of structure on load. T he results of the present work also provide a method (based on spectral ana lyses) that can be used for studying micromechanisms accounting for shear d eformation and failure. (C) 1999 Elsevier Science Ltd. All rights reserved.