Phase behaviour and mechanical properties of epoxy resin containing phenolphthalein poly(ether ether ketone)

Blends of bisphenol-A-type epoxy resin(ER) and phenolphthalein poly(ether ether ketone) (PEK-C) cured with 4,4'-diaminodiphenylmethane (DDM) were studied using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM). The phase behaviour of the DDM-cured ER/PEK-C blends was greatly dependent on the curing condition and was affected by both the thermodynamic and kinetic factors. The homogeneous DDM-cured ER/PEK-C blends were obtained. The studies of DSC and Fourier-transform infrared (FTi.r.) spectroscopy indicate that there existed some unreacted oxirane rings of ER in the blends, and the curing reaction was incomplete even though the samples of the blends were further post-cured at 250 degrees C. Mechanical measurements show that incorporation of PEK-C slightly decreased both the fracture toughness (K-IC and G(IC)) and the flexural properties, presumably due to the reduced cross-link density of the epoxy network. SEM observation of the surfaces of fracture mechanical measurement specimens indicates the nature of brittle fracture for the plain ER and the blends. (C) 1997 Elsevier Science Ltd. All rights reserved.