Dynamic mechanical behavior and interphase adhesion of thermoplastic (PEEK, PES) short fiber composites

The dynamic mechanical behavior of four thermoplastic composite systems is investigated between 50 and 250 degrees C. Poly(etheretherketone) (PEEK) and poly(ethersulfone) (PES) are reinforced with 0-30 wt. % short glass (GF) and carbon fibers (CF) and then microstructurally characterized. Fiber length distributions and orientation in the injection molded samples are determined by quantitative optical microscopy and scanning electron microscopy (SEM) respectively. The mechanical damping (tan delta) and storage modulus (E') are studied for a given microstructure in the context of the properties of the various constituents of composites. The quantitative analysis of the tan delta depression of composites at the glass transition temperature (T-g) is interpreted in terms of fiber-matrix interphase adhesion. This study reveals that, in contrast to carbon fibers, which are seen to adhere better to PEEK, glass fibers adhere better to PES. SEM observations of fractured surfaces of composites corroborate the estimations about fiber-matrix adhesion obtained by Dynamic Mechanical Thermal Analysis (DMTA).