DYNAMIC-MECHANICAL BEHAVIOR AND INTERPHASE ADHESION OF THERMOPLASTIC (PEEK, PES) SHORT-FIBER COMPOSITES

The dynamic mechanical behavior of four thermoplastic composite system s is investigated between 50 and 250 degrees C. Poly(etheretherketone) (PEEK) and poly(ethersulfone) (PES) are reinforced with 0-30 wt. % sh ort glass (GF) and carbon fibers (CF) and then microstructurally chara cterized. Fiber length distributions and orientation in the injection molded samples are determined by quantitative optical microscopy and s canning electron microscopy (SEM) respectively. The mechanical damping (tan delta) and storage modulus (E') are studied for a given microstr ucture 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, i n contrast to carbon fibers, which are seen to adhere better to PEEK, glass fibers adhere better to PES. SEM observations of fractured surfa ces of composites corroborate the estimations about fiber-matrix adhes ion obtained by Dynamic Mechanical Thermal Analysis (DMTA).