The objective of this study was to investigate the processability, mechanical properties, and electrical properties of carbon black‐filled ethylene‐vinyl acetate (EVA) copolymers with different melt flow indexes (MFIs) and vinyl acetate (VA) contents. The effects of carbon black on maximum temperature, equilibrium torque, equilibrium viscosity, and work energy were characterized in a Haake torque rheometer. These properties were found to increase with an increase in carbon black concentration. MFI was found to be the important factor in determining processing properties of the three different EVA resins. Mechanical properties, including tensile modulus, tensile strength at break, and elongation at break were evaluated and the results showed that tensile modulus was dominated by VA content. MFI was the primary factor influencing tensile strength and elongation at break. Volume and surface resistivity of blends were also studied. EVA with higher MFI and higher crystallinity provided a lower percolation concentration. Bound polymer could be used to explain the differences in viscosity and percolation between EVAs at different molecular weights. © 2000 John Wiley & Sons, Inc. Adv Polym Techn 19: 132–139, 2000

The objective of this study was to investigate the processability, mechanical properties, and electrical properties of carbon black-filled ethylenevinyl acetate (EVA) copolymers with different melt flow indexes (MFIs) and vinyl acetate (VA) contents. The effects of carbon black on maximum temperature, equilibrium torque, equilibrium viscosity, and work energy were characterized in a Haake torque rheometer. These properties were found to increase with an increase in carbon black concentration. MFI was found to be the important factor in determining processing properties of the three different EVA resins. Mechanical properties, including tensile modulus, tensile strength at break, and elongation at break were evaluated and the results showed that tensile modulus was dominated by VA content. MFI was the primary factor influencing tensile strength and elongation at break. Volume and surface resistivity of blends were also studied. EVA with higher MFI and higher crystallinity provided a lower percolation concentration. Bound polymer could be used to explain the differences in viscosity and percolation between EVAs at different molecular weights.

The objective of this study was to investigate the electrical conductivity of polypropylene (PP)/Carbon Black (CB) blends, Ethylene-Vinyl Acetate (EVA)/CB blends, and ternary blends of PP, EVA, and CB. PP/CB and EVA/CB blends were prepared in a Haake rheometer. Both volume and surface resistivities of PP/CB blends showed a percolation around 4 wt % CB. PP/EVA/CB blends were made by compounding a 30/70 CB/EVA blend with PP in a Brabender twin screw extruder to maintain a constant ratio between EVA and CB. The conductivity of PP/EVA/CB samples showed a dependence on processing history. Both volume and surface resistivity of the samples extruded once showed only a small decrease between 3 and 7.5 wt % CB. After three extrusions the resistivity of 3 wt % CB increased substantially and the resistivity of 7.5 wt % CB decreased slightly. The samples extruded three times had a lower standard deviation. Calculated surface tension indicated that CB preferentially distributed in EVA phase.Multiple pass in the twin screw extruder decreased phase size and accounted for the change of resistivity.

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