Simultaneous enhancements in electrical conductivity and toughness of selectively foamed polycarbonate/polystyrene/carbon nanotube microcellular foams

Electrically conductive polycarbonate/polystyrene/carbon nanotube (PC/PS/CNT) ternary nanocomposites are prepared by blending with styrene-maleic anhydride copolymer as their compatibilizer. Interestingly, CNTs are selectively distributed in PC phase in the PC/PS/CNT nanocomposites. After foaming with supercritical carbon dioxide as the foaming agent, most cells preferentially localize in the readily foamed PS phase; whereas, few cells appear in the PC matrix. Therefore, a selectively foamed morphology consisting of electrically conductive PC/CNT continuous phase and the foamed PS dispersed phase is well constructed. Due to the selective localization of CNTs, the PC70/PS30/CNT nanocomposite foams with PC as the matrix exhibits a much lower conducting percolation threshold of 0.35 vol% than the PC30/PS70/CNT nanocomposite foams with foamed PS as the matrix (0.94 vol%). The high electrical properties of the PC70/PS30/CNT foams are attributed to the conducting network of CNTs within the continuous PC matrix and the volume-exclusion effect of the preferentially foamed PS dispersed phase. More interestingly, PC70/PS30/1%CNT nanocomposite foam also exhibits much higher mechanical properties than PC30/PS70/1%CNT nanocomposite foam and a significant increase of 245% in notched Izod impact strength is achieved in relative to its bulk counterpart due to the toughening effect of the foamed PS particles.