Study On Conductive Multiphase Polymer Composites Filled With Carbon Black

Conductive polymer composites have been extensively used in many fields of electronic, energy and chemical engineering. To ensure a high conductivity, conducting fillers are requested more loading, namely, a high content of the fillers in the composites. A typical example is that it is requested to add more than 20% conductive carbon black (CB) in the composite to form conducting network. However, high concentration of fillers results in some disadvantages for the composites, such as high melting viscosity, poor processability and mechanical properties. Hence, lowering the content of conducting filler in a composite is of importance for improving the properties of the composites.A series of ternary and binary conductive polymer composites of polypropylene (PP), the low density polyethylene (LDPE) and carbon black (CB) were prepared by melt-mixing method. Based on the concepts of double percolation, conductive composites with lower electrical percolation can be prepared. The morphology, crystallization, rheology and positive temperature coefficient (PTC) of the composites were discussed.Conductivity measurement indicates that the ternary composite CB/PP/LDPE has lower electrical percolation threshold than the binary composites of CB/PP or CB/LDPE. The reason is attributed to the fact that the majority of CB will be selectively located in the LDPE domains of the ternary blends. When the ratio of PP/LDPE is 8/2 (wt), the ternary composites exhibit a relative lower conductive threshold value (4.9%). Based on the SEM micrographs analysis, CB is found to be selectively located in LDPE domains. Meanwhile, the electrical threshold also depends on the adding sequence of the components. Rheological behavior of the multiphase composites exhibits a very strong shear thinning effect. At low frequencies, the rheological behavior of the composites shows dependence of frequency for <5.0 wt% CB filler. At high frequencies, the fraction of CB has a relative minor influence on the rheological behavior of the composites, indicating solid-like behavior, which suggests the formation of a network structure. The rheological percolation value is 2.66 wt%, which is significantly smaller than the electrical percolation (4.9 wt%). This can be explained that the CB distances required for rheological is smaller than the electrical percolation.PTC effect is related to the continuous phase transition, and PTC effect is believed to be a special critical phenomenon caused by the change in both temperature and the filler mass fraction. The PTC intensity for the ternary composites can be enhanced by comparing the ternary and binary composites. Based on the conductivity dependence of temperature with different CB mass fraction in ternary blends, it is obvious that during the PTC transition, the PTC intensity is higher with CB mass fraction around electrical percolation threshold than the other CB loadings.The addition of PP has an obvious influence on the crystallization of LDPE, indicating that CB selectively locates in LDPE domains. The critical value of CB for non-isothermal crystallization is 5 wt%. That is concerned the electrical percolation (4.9 wt%) of the conductive network in the composites. The ternary composites exhibit better mechanical properties than the binary ones.