Effect of processing parameters on electrical resistivity and thermo-sensitive properties of carbon-black/styrene–butadiene–rubber composite membranes

Carbon-black-filled conducting composite membranes were prepared by using styrene–butadiene–rubber as matrices and incorporating with some organic crystals (2,6-di-tert-butyl-4-methyl phenol). A number of composite membranes exhibited a thermo-sensitive property which corresponded to a positive temperature coefficient (PTC) effect. It was found that processing parameters strongly affected the microstructure of composite membranes and in turn, the resistivity of membranes as well as their PTC characteristics. The effect of several main processing parameters, such as mixing parameters (temperature, time and nip gap) and vulcanization parameters (temperature, time and pressure), on the resistivity and PTC characteristic of composite membranes was investigated. The results obtained from resistivity measurements, DSC thermograms, SEM micrographs and X-ray diffraction patterns revealed that, by using optimized mixing and vulcanization parameters, the obtained composite membranes showed a microcrystal-embedded structure and their resistivity against carbon black content exhibited a tangible percolation behavior. It was also found that the PTC characteristics of some composite membranes prepared by optimized processing parameters appeared to be stable for an acceptable long term.