TEMPERATURE DEPENDENCES OF ELECTRICAL CONDUCTIVITY IN CARBON BLACK FILLED POLYMER BLENDS

Abstract

The dispersion state of carbon black (CB) in polymer blends which are incompatible with each other and temperature dependences of electrical conductivity of these composities were studied. The electrical conductivity of composities was measured as a function of temperature in heating and cooling cycles. It was found that CB distributes unevenly in each component of the polymer blend. This uneven distribution of fillers in polymer blend matrices has much effect on the electrical conductivity of composites and their temperature dependences. The extent of PTC (Positive Temperature Coefficient of resistivity) of composites depends on the blend ratio of filler rich phase and dispersion state of CB in this phase. The electrical conductivity of CB filled crystalline polymer blends composed of high density polyethylene (HDPE) and polypropylene (PP) shows a prominent PTC below melting temperature and rapid decrease (NTC) above it at particular blend ratio of HDPE. However, the electrical conductivity of CB filled crystalline and amorphous polymer blend, i.e., HDPE/PMMA (poly (methyl methacrylate)) does not show such a large temperature dependences of conductivity at same blend ratio of HDPE. This prominent temperature dependence of conductivity is due to the changes of inter-conductive domain-gap of filler rich phase (HDPE), accompained with thermal expansion of another crystalline polymer, PP.