No abstract

Octamethyl-POSS-HDPE nanocomposites were prepared by the melt mixing route. The rheological and viscoelastic behavior of HDPE-octamethyl-POSS nanocomposites was investigated with a strain-controlled rheometer and dynamic mechanical analysis (DMA). The rheological results show that while at lower filler concentration (0.25-0.5 wt %) POSS particles act as lubricant and reduce the complex viscosity of the nanocomposites, at higher concentrations, viscosity increases. POSS remains miscible in HDPE at lower concentrations and lower temperatures used in the study; however it starts aggregating at higher concentrations and higher temperatures. The presence of POSS particles causes gelation in HDPE matrix at concentrations higher than 5 wt % possibly due to the segregated particle-particle interaction. The storage modulus shows an increase at lower POSS concentrations but decreases at higher POSS concentrations. The R-transition temperatures shift to higher values at low POSS concentrations and is attributed to restriction of the movement of HDPE chain segments in the intercrystalline regions due to the presence of POSS macromers around the crystallite boundaries. The effect of POSS on morphology of HDPE was studied with X-ray diffraction and DSC techniques. It was observed that while POSS does not interfere with the crystallization of HDPE, it crystallizes itself into nanocrystals.

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This paper investigates the relationship between cure temperature, morphology, and mechanical properties of di-, tri-, and tetrafunctional high-performance, epoxy layered-silicate nanocomposites. 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.