The electrical resistivity and morphology of polypropylene/nylon (PP/Ny) immiscible blends incorporated with carbon black (CB) were studied. CB was found to be preferentially located in the Ny phase or upon the Ny/PP interface. Blends with a co‐continuous phase morphology depicted especially low resistivity values, due to a “double percolation” effect. The blend preparation sequence tends to affect the phase morphology, thus influencing the system's resistivity. Polymer polarity and crystallinity are important factors determining the blend's morphology, which relates directly to the electrical resistivity obtained.

This paper discusses the feasibility of the application of conductive immiscible polymer blends as sensor materials for detection of organic liquid solvents. Immiscible polymer blends of polypropylene (PP). nylon 6 (Ny6) and carbon black (CB) have been used to produce a series of electrically conductive b e n t s by a capillary rheometer process. In these immiscible blends, PP serves as a semi-crystalline matrix and Ny6 as the semi-crystalline dispersed phase. The enhancement of conductivity in these blends is due to the attraction of CB to Ny6 and localization of CB particles at the PP/Ny6 interface, giving rise to conductive networks. The dc electrical resistivity of extruded filaments, produced at different shear levels, is found to be sensitive to various organic liquid solvents. The shear rate at which the filaments are produced has an important effect on the PP/Ny6/CB filament's sensitivity. The compositions studied were close to the double-percolation structure believed to perform best as sensor materials. In addition, it seems that the PP/Ny6 interface plays a major role in the sensing process. Liquid contact/drymg cycling of the filaments indicates stabilization of the sensitivity change making the sensing process reversible.

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Immiscible polymer blends based on polypropylene/thermoplastic polyurethane (PP/TPU) are interesting host multiphase systems for the incorporation of low concentrations of conductive carbon black (CB) particles. The enhancement of conductivity (and the lower critical CB content for percolation) in the PP/TPU blend is achieved via double percolation, that is, structural and electrical. The CB particles form chainlike network structures within the TPU phase, which exhibit phase continuity of elongated particles within the PP matrix. Moreover, scanning electron microscopy and dynamic mechanical thermal analysis studies indicated that the incorporation of CB particles into the PP/TPU blend has a "compatibilizing" effect, resulting in an enhanced interaction between the two polymers. Extruded PP/TPU/CB filaments produced by a capillary rheometer process at various shear rates were examined as sensing materials for a homologous series of alcohols, that is, methanol, ethanol, and 1-propanol. All filaments displayed increasing resistance upon exposure to the various alcohols combined with excellent reproducibility and recovery behavior. An attempt is made to identify the dominant mechanisms controlling the sensing process in a CB-containing immiscible polymer blend characterized by a double-continuity structure. The interphase region, its quantity, and continuity played a significant role in the liquidtransport process. Blend composition, filaments' extrusion temperature, and production shear rate level were considered as significant parameters determining the structure and the resultant sensing properties.

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ABSTRACT:The structure/electrical resistivity relationship in CB-loaded immiscible HIPS/LLDPE blends was studied. Effects of CB content and location, dispersed polymer phase size and shape, dispersed phase viscosity, and processing procedures were examined. The elongated dispersed phase in CB-containing blends is essential for promoting conductivity in formulations prepared by melt mixing and compression molding. However, the same formulations proved highly resistive when injection-molded, due to orientation and excessive shearing.

Immiscible polymer blends based on high-impact polystyrene/ethylene vinyl acetate (HIPS/EVA) are interesting host multiphase systems for the incorporation of low concentrations of carbon black (CB). The conductive filler CB tends to accumulate preferentially within the EVA phase, forming segregated structures, and thus conductivity of the blends is only obtained when double percolation is realized. Material properties such as surface tension and crystallinity of the CB-containing polymer are found to influence filler distribution, accordingly affecting the electrical conductivity. A rheological-electrical method is presented, whereupon extrudates of CB-containing binary immiscible polymer blends are produced by a capillary rheometer, and the effect of shear level on the extrudates' structure and resultant resistivity is determined. A descriptive model was derived, illustrating the effect of shear on double percolation at various blend compositions. The flow behavior of the CB-containing compounds was studied in regard to the filler packing factor, m , and related to the electrical properties of the extrudates. Blend composition, CB content, and shear level were considered as significant parameters, determining the structure and the resultant electrical properties.

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