Maintaining electrical conductivity of microcellular MWCNT/TPU composites after deformation

Along with stretching ability, maintaining good electrical conductivity has become one of the most desirable properties for the next-generation electronics. Although various fabrication methods have been suggested, the greatest obstacle is their feasibility for large-scale production with low cost. In this study, highly stretchable and conductive MWCNT/TPU composite foams were fabricated by an industrially viable technique, melt compounding followed by supercritical fluid treatment and physical foaming. It was demonstrated that the introduction of a microcellular structure can significantly suppress increase in the electrical resistance with stretching. The 3.1 vol% MWCNT/TPU composite exhibited electrical conductivity of 9.5 × 10−4 S/cm, which reduced to 1.7 × 10−5 S/cm with 100% stretching. The creation of 26% void fraction increased the conductivity to 1.9 × 10−3 S/cm and assisted in maintaining a constant level of the electrical conductivity with 100% stretching. This is attributed to the localized deformation around the cells. Since the deformation is localized around the cells, the filler interconnections away from the cells are less deformed, and hence can maintain a high level of electrical conductivity. It was further found that the effect of localized deformation enhances the elongating ability of the MWCNT/TPU composites. This study shows that the generation of a microcellular structure offers a very effective way of fabricating highly stretchable and conductive polymeric materials for future electronics.