Poly(ether ether ketone)/poly(aryl ether sulfone) blends: Melt rheological behavior

Dynamic rheological measurements were carried out on blends of poly(ether ether ketone) (PEEK)/poly(aryl ether sulfone) (PES) in the melt state in the oscillatory shear mode. The data were analyzed for the fundamental rheological behavior to yield insight into the microstructure of PEEK/PES blends. A variation of complex viscosity with composition exhibited positive-negative deviations from the log-additivity rule and was typical for a continuous-discrete type of morphology with weak interaction among droplets. The point of transition showed that phase inversion takes place at composition with a 0.6 weight fraction of PEEK, which agreed with the actual morphology of these blends observed by scanning electron microscopy. Activation energy for flow, for blend compositions followed additive behavior, which indicated that PEEK/PES blends may have had some compatibility in the melt. Variation of the elastic modulus (G') with composition showed a trend similar to that observed for complex viscosity. A three-zone model used for understanding the dynamic moduli behavior of polymers demonstrated that PEEK follows plateau-zone behavior, whereas PES exhibits only terminal-zone behavior in the frequency range studied. The blends of these two polymers showed an intermediate behavior, and the crossover frequency shifted to the low-frequency region as the PEEK content in PES increased. This revealed the shift of terminal-zone behavior to low frequency with an increased PEEK percentage in the blend. Variation of relaxation time with composition suggested that slow relaxation of PEEK retards the relaxation process of PES as the PEEK concentration in the blend is increased because of the partial miscibility of the blend, which affects the constraint release process of pure components in the blend. A temperature-independent correlation observed in the log-log plots of G' versus loss modulus (G) for different blend systems fulfilled the necessary condition for their rheological simplicity. Further, the composition-dependent correlations of PEEK/PES blends observed in a log-log plot of G' versus G showed that the blends are either partially miscible or immiscible and form a discrete-continuous phase morphology. (C) 2004 Wiley Periodicals, Inc.