Effect of dynamic cross-linking on melt rheological properties of polypropylene/ethylene-propylene-diene rubber blends

Study of melts rheological properties of unvulcanized and dynamically vulca nized polypropylene (PP)/ethylene-propylene-diene rubber (EPDM) blends, at blending ratios 10-40 wt %, EPDM, are reported. Blends were prepared by mel t mixing in an internal mixer at 190 degrees C and rheological parameters h ave been evaluated at 220 degrees C by single screw capillary rheometer. Vu lcanization was performed with dimethylol phenolic resin. The effects of (i ) blend composition; (ii) shear rate or shear stress on melt viscosity; (ii i) shear sensitivity and flow characteristics at processing shear; (iv) mel t elasticity of the extrudate; and (v) dynamic cross-linking effect on the processing characteristics of the blends were studied. The melt viscosity i ncreases with increasing EPDM concentration and decreased with increasing i ntensity of the shear mixing for all compositions. In comparison to the unv ulcanized blends, dynamically vulcanized blends display highly pseudoplasti c behavior provides unique processing characteristics that enable to perfor m well in both injection molding and extusion. The high viscosity at low sh ear rate provides the integrity of the extrudate during extrusion, and the low viscosity at high shear rate enables low injection pressure and less in jection time. The low die-swell characteristics of vulcanizate blends also give high precision for dimensional control during extrusion. The property differences for vulcanizate blends have also been explained in the light of differences in the morphology developed. (C) 2000 John Wiley & Sons, Inc.