| Phase continuity development and co-continuous morphologies are highly influenced by the nature of the interface in immiscible polymer blends. Broadly, the interfaces can be classified as binary compatible, binary incompatible, and ternary compatible type. This thesis evaluates morphology, continuity development and cocontinuity in polymer blends of low interfacial tension, i.e. binary compatible type of interface. The effect of dynamic crosslinking on the continuity and cocontinuity is also examined.; Besides considerable commercial significance, an ultra-low interfacial tension between ethylene-propylene-diene terpolymer (EPDM) and polypropylene (PP) makes this system an ideal model for such investigations. Using the harmonic mean equation, the value of interfacial tension between these materials is estimated to be 0.3 mN/m at a melt blending temperature of 190°C. Overall, EPDM/PP blends of viscosity ratios from 0.1-17.0, elasticity ratios from 0.1-29, and matrix shear stresses from 11.7-231.4 kPa were prepared by melt mixing in an internal mixer. The blend components are shown to be completely immiscible with each other after cooling from the melt.; In EPDM/PP blends of low to medium viscosity ratios (0.2-5.0), using scanning electron microscopy (SEM) and atomic force microscopy (AFM) it is shown that the dispersed phase is distributed very uniformly and forms very fine domains, only of a few hundred nanometers in diameter. Contrary to current belief, by selectively dissolving the matrices it is shown that the dispersed phase in this blend system actually exists in the form of stable nano-fibers of about 50-200 nm in diameter. An analysis of thread break-up times from Tomotika theory also supports the notion of highly stable dispersed fiber formation.; With an increase is composition of minor phase, these fibers are shown to coalesce at crossover points to develop continuity. Thus, the system achieves cocontinuity by fiber-fiber coalescence. The continuity development for both the blend components is studied. In all these experiments, whenever it was necessary to dissolve the PP phase without dissolving the EPDM phase, the EPDM phase was irradiation crosslinked after melt blending. A highly symmetrical and identical continuity development with respect to mid-composition is observed at these low to medium viscosity ratios. In fact, a single master curve for the continuity development can be drawn for these blends. The particle sizes are also observed to be insensitive to the variations in viscosity ratio; however, an 8-fold variation in the shear stress has an effect. (Abstract shortened by UMI.)... |
