The interrelation between morphology, resistivity, and flow properties of carbon black-containing HIPS EVA blends

Immiscible polymer blends based on high-impact polystyrene/ethylene vinyl a cetate (HIPS/EVA) are interesting host multiphase systems for the incorpora tion of low concentrations of carbon black (CB). The conductive filler CB t ends to accumulate preferentially within the EVA phase, forming segregated structures, and thus conductivity of the blends is only obtained when doubl e percolation is realized. Material properties such as surface tension and crystallinity of the CB-containing polymer are found to influence filler di stribution, accordingly affecting the electrical conductivity. A rheologica l-electrical method is presented, whereupon extrudates of CB-containing bin ary immiscible polymer blends are produced by a capillary rheometer, and th e effect of shear level on the extrudates' structure and resultant resistiv ity is determined. A descriptive model was derived, illustrating the effect of shear on double percolation at various blend compositions. The flow beh avior of the CB-containing compounds was studied in regard to the filler pa cking factor, phi(m), and related to the electrical properties of the extru dates. Blend composition, CB content, and shear level were considered as si gnificant parameters, determining the structure and the resultant electrica l properties. (C) 1999 John Wiley & Sons, Inc.