Positive temperature coefficient of resistivity (PTCR) characteristics of poly(styrene‐co‐acrylonitrile) copolymer (SAN)/stainless steel (SS) powder (80 wt %) composites prepared by melt‐mixing method has been investigated with reference to SAN/carbon black (CB) composites. The SAN/CB (10 wt %) composites showed a sudden rise in resistivity (PTC trip) at 125°C, above the glass transition temperature ( T g ) of SAN ( T g ≈ 107°C). However, the PTC trip temperature of SAN/SS (80 wt %) composites appeared at 94°C, well below the T g of SAN. Addition of 1 phr of nanoclay increased the PTC trip temperature of SAN/CB (10 wt %) composites to 130°C, while SAN/SS (80 wt %)/clay (1 phr) nanocomposites showed the PTC trip at 101°C. We proposed that the mismatch in coefficient of thermal expansion (CTE) between SAN and SS played a key role that led to a disruption in continuous network structure of SS even at a temperature below the T g of SAN. The dielectric properties study of SAN/SS (80 wt %) composites indicated possible use of the PTC composites as dielectric material. DMA results showed higher storage modulus of SAN/SS composites than the SAN/CB composites.
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Kar et al. (2011) studied this question.
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