Polymer composites filled with conductive particles such as metal, carbon black (CB) and nanotube (CNT) exhibit electro conductivity, and their resistivity significantly increases with raising temperature. Particularly, semicrystalline polymer composites possess superior electro conductivity and positive temperature coefficient (PTC) effect, because conductive particles effectively connect by localizing in the amorphous phase and disconnect by a greater volume expansion near the melting point. In this study, we quantitatively analyzed the PTC effect of various composites consisting of semi-or non-crystalline polymers filled with metal or carbon particles by calculating their filler contents considering thermal volume expansion rate and degree of crystal, as a guideline for design of sensor and circuit protection devices. The revised filler content at room temperature, φ (R.T.) of poly (vinylidene fluoride) (PVDF) / nickel, CB and CNT as semicrystalline polymer composites became higher than the amount of filler loading in preparation and drastically decreased as temperature increased. In contrast, φ (R.T.) of poly (methyl methacrylate)(PMMA) / CB and CNT as noncrystalline polymer composites gradually decreased with temperature. The rate of the revised filler content at PTC, φ (PTC) and φ (R.T.) at various amounts of filler loading in preparation was a constant value in each composite, and φ (PTC) / φ (R.T.) values of PVDF / Ni, PVDF / CB,PVDF / CNT. PMMA / CB and PMMA / CNT were 0.93, 0.78, 0.74, 0.95 and 0.96, respectively. These values indicate the filler content necessary to occurring PTC effect. In comparison of each φ (PTC) / φ (R.T.) value, semicrystalline polymer and carbon filler systems were lower. The results well represent the effect of particle localization in the amorphous phase of semicrystalline polymer and strong interaction of carbon nanofillers for the PTC characteristics.

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