This paper presents the rheology and morphology of immiscible polymer blends compatibilized by a polymer reaction at the interface. Nylon-6 was melt blended in a twin screw extruder with several different grades of maleated polypropylene at 10 and 20 wt %. The extent of polymer reaction at the interface is varied by varying the extent of maleation of polypropylene and affects the phase morphology differently at different phase volume fractions. The rheology of the reactive blends is fit to the Palierne theory to infer values of the equilibrium interfacial tension. The equilibrium interfacial tension of the reactive blends is reduced in proportion to the extent of maleation of the polypropylene. In blends with more reaction product, another mechanical property of the interface is required to fit the low-frequency data well.

The structure of nanocomposites produced by melt-mixing polypropylene and 5 wt % of organically modified layered silicates with varying amounts of different maleated polypropylene compatibilizer grades has been analyzed with X-ray diffraction, transmission electron microscopy (TEM), and melt rheology. The extent of delamination in different nanocomposites has been quantified from analysis of several TEM images for each specimen by a product of the single particle volume fraction and the intrinsic viscosity of such particles. This measure correlated directly with the low shear relative viscosity of the molten composites (relative to the silicate free mixture of polypropylene and compatibilizer). The results also indicate that the acid number alone is not a good predictor of compatibilizer effectiveness, i.e., the amount required for exfoliation. The molar ratio of functional groups to compatibilizer chains is found to be a better parameter for ranking compatibilizer effectiveness than the acid number, which is a weight ratio. With higher values of the molar ratio, lower concentrations of compatibilizer are required for significant exfoliation. With the highest molar ratio compatibilizer, an optimum compatibilizer concentration of about 10 wt % leads to a composite with the most exfoliated structure.

No abstract

This work presents new results on using organoclay with an appropriate polymeric compatibilizer as rheology-modifying additives for extrusion foaming of a linear polypropylene (PP), which by itself does not display strain hardening in extensional flow of the melt. The uniaxial melt-extensional viscosity behavior of several nanocomposites prepared with varying ratio of bound maleic anhydride to clay as well as varying compatibilizer molecular weight was investigated. A chemicalblowing agent was used at a fixed concentration for foaming these nanocomposites in a single-screw extruder. Among nanocomposites with similar levels of clay dispersion or intercalation, the ones that displayed significant strain hardening in the melt state along with slower crystallization led to extruded PP nanocomposite foams with smaller cell sizes and greater cell density by reducing cell coalescence. This was achieved with as little as 3 wt% organoclay and a high-molecular weight

SUMMARYA continuation method has been used with a ÿnite element grid and a geometric perturbation to compute two successive symmetry breaking ow transitions with increasing Reynolds number in ow of generalized Newtonian uids through a sudden planar expansion. With an expansion ratio of 16, the onset Reynolds number is particularly sensitive to small geometric asymmetry and the critical Reynolds numbers for the two successive ow transitions are found to be very close. These transitions are delayed to higher onset Reynolds numbers by increasing the degree of pseudoplasticity. This trend is observed experimentally as well in this work and may be attributed to the competing e ects of shear thinning and inertia on the size of the corner vortex before the symmetry breaking ow transition. After the second transition with an expansion ratio of 16, the two large staggered vortices on opposite walls occupy most of the transverse dimension so that the core ow between the vortices appears as a thin jet oscillating along the ow direction. This is more pronounced for the pseudoplastic liquid. After the second transition, the degree of ow asymmetry at a given location downstream of the expansion plane is larger for the pseudoplastic liquid than for the Newtonian liquid at comparable Reynolds numbers. The last feature is also evident in the experimentally observed velocity proÿles.