Development of conductive polyimide/polysulfone composites as positive temperature coefficient materials

Abstract

For positive temperature coefficient (PTC) applications of electrically conductive composites, volume resistivity at room temperature of lower than 104 Ω.cm is one major requirement. Conductive polyimide (PI) PTC with the above level of conductivity value can be achieved by a use of carbon black (CB) as conductive filler. For materials with PTC, there is a change in resistance related to temperature. In order to reduce the amount of CB used in the PTC composites, one of well-known methods is to introduce another polymer into a polymer to generate immiscible blends. When the conductive filler is dispersed in one polymer phase, a system of double percolation with minimal filler content can be achieved. When heating the conductive composite beyond the glass transition temperature, the conductive state of the system changes to insulated state. In this research, conductive composites in materials with PTC are prepared by polymerization between PI and polysulfone (PSF) at a ratio of 100/0 to 10/90 by weight, using CB with loading from 0 to 20% by weight. From the study, it is found that polymer blends between PI/PSF behaved as partially miscible in nature. The blends evidently provided a reduced percolation threshold by 90% with the obtained greater electrical conductivity values than those of the CB-filled PI composites. Considering the volume resistivity of the conductive composite with the change in temperature, it is found that the behavior is PTC material at a temperature range of 180 to 200 oC. Optical microscopic has been used to verify the preferential location of the conductive CB particles in PI domains rather than in the PSF domains. Moreover, the obtained tensile and thermal properties of conductive composites were also found to provide the values meet those standards. The results, therefore, revealed the potential to apply the obtained PTC composites in electronic applications.