PEEK polymer filled with PTFE particles (PTFE/PEEK) is widely used in ad-vanced tribological composites for modern rotating and reciprocal machinery. De-sign, manufacturing and tribological evaluation of the composite require clear un-derstanding of high-temperature dynamic mechanical behavior of the material sys-tem. In this paper, a comprehensive study is reported on determination of elevated-temperature dynamic mechanical behavior of the PTFE/PEEK composite. The study involves combined experimental investigation and theoretical modeling and analysis of PTFE/PEEK microstructure and morphology, transition states and dy-namic mechanical properties up to 250°C (373°F). Optical and SEM micrographs of the PTFE/PEEK composite reveal microstructure features of PTFE particulates in the PEEK matrix. Crystallinity of the PEEK matrix in the composite is found to change slightly whereas crystallinity of the PTFE phase decreases significantly with the increase of the PTFE volume fraction. The PTFE/PEEK exhibits multiple transi-tions during temperature excursion with its glass transition appearing near 150°C (302°F) and a secondary transition at room temperature. High-temperature dynamic mechanical behavior of the composite is determined; its thermoelastic modulus de-creases with increasing temperature and drops dramatically by orders of magnitude at glass transition but loss modulus and tanδ increase with temperature, reaching their maxima at T_g. The amount of PTFE addition significantly affects composite thermomechanical properties: at high temperature near and above its glass transition, increasing the PTFE volume fraction raises the composite tanδ but decreases ther-moelastic and loss moduli, but below T_g, increasing the PTFE phase decreases both, with the most significant reduction at a low PTFE volume fraction. The results are of significant importance in understanding the fundamental nature of transitions and elevated-temperature dynamic mechanical behavior of the PTFE/PEEK composite and also provide a foundation for a subsequent study of friction and wear resistance of the modern tribological composites.
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