Layered silicate nanocomposites based on various high-functionality epoxy resins: the influence of cure temperature on morphology, mechanical properties, and free volume

This paper investigates the relationship between cure temperature, morphology, and mechanical properties of di-, tri-, and tetrafunctional high-performance, epoxy layered-silicate nanocompoaites. Wide-angle X-ray analysis (XRD) was carried out at different stages of cure to monitor organoclay exfoliation kinetics. It was found that some (small) degree of conversion was required to obtain significant intercalation. The nanocomposite morphology was also probed using transmission electron microscopy, XRD, and positron annihilation lifetime spectroscopy. The bifunctional DGEBA resin gave better exfoliation than the resins of higher functionalities. This is attributed to better catalysis of the intragallery reaction by the organo-ions which reside within the galleries. Higher cure temperatures were also found to improve clay delamination and simultaneously increased toughness and modulus in case of the DGEBA- and TGAP-based materials. Free volume properties did not vary significantly between resins or with cure temperature and generally followed the rule of mixtures, although there was a suggestion that the presence of clay leads to increased free volume. This was consistent with decreased glass transition temperatures upon addition of layered silicate, ascribed to disruption, and decreased cross-link density in interfacial regions of clay and epoxy matrix.