ABSTRACT:The mechanical properties of blends of isotactic polypropylene (PP) and poly[ethylene-co-(vinyl acetate)] (EVA) are studied under tension at several temperatures (from -30• C to room temperature). The morphology and thermal properties are given attention at every stage of the stretching process. To improve the impact resistance of the blends, poly[propylene-graft-(maleic anhydride)] (PPMA) and hydroxylated EVA (EVAOH) are used as compatibilizers. The domain size of the dispersed phase decreases with compatibilizer content, improving the impact resistance of the blends. This is accompanied with changes in the morphology of such systems. C

The slip flow of the polypropylene (PP)/poly[ethylene-co-(vinyl acetate)] (EVA) system was studied in a capillary rheometer for shear rates of 40 -1000 s Ϫ1 at four temperatures. Three dies made of aluminum with a length/diameter (L/D) ratio of 15 and diameters of 1.59, 1.19, and 0.79 mm provided the flow data. Calculations of the slip velocity by the Mooney method showed power-law behavior with the stress. Blends were prepared at various proportions of PP and EVA for observation of the variation of the slip velocity for different compositions and temperatures. Direct microscopic observations of the slip layer on extruded samples showed domains of the dispersed phase unevenly distributed between the slip layer and the core and provided estimates of the thickness of the layer adjacent to the capillary wall. Results showed that the viscosity in the slip layer was 10 -100 times lower than that in the bulk for the same value of the shear stress. In terms of the extrapolation length, the development of the slip layer was the result of different disentanglement dynamics of the molecules in the slip layer in comparison with those in the bulk.

Polyethylene terephthalate (PET) and polyethylene 2, 6 naphthalene dicarboxylate (PEN) nanocomposites were prepared by an extrusion process with organic‐modified montmorillonite clay. The steady‐state viscosity of all blends diminished as compared to the system with no clay added. A rheological study was conducted to know more about the complex structure formed by the polymer matrix‐clay interactions. Instantaneous stress relaxation curves are presented for the PEN, PEN‐PET and PET‐PEN‐1phr clay systems. A Fourier Transform (FT) frequency response was obtained from the relaxation curves and compared to the linear oscillatory data, which lead to an extended frequency region. The results were modeled by a rheological equation of state which accounts for the formation‐destruction dynamics of the microstructure during flow. Relaxation time spectra are presented and compared for both rheological tests, namely, instantaneous stress relaxation and linear oscillatory flow. Additional studies using scanning electron microscopy (SEM) are presented, which reveal the presence of a slip layer in capillary flow for the system with added clay.

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Several polypropylene–ethylene vinyl acetate (PP/EVA) copolymers with compositions ranging from 90/10 to 10/90 PP/EVA were prepared and characterized in terms of their morphology by transmission and scanning electron microscopy, and their mechanical properties were also studied. The results show a wide range of spatial structures which correlate well to the corresponding measurements of elastic modulus of the blends.