The development of a conductive carbon nanotube (CNT) network in CNT/polypropylene composite films during biaxial stretching

Two developing stages of conducting network in carbon nanotube (CNT)/polypropylene composite films were found during simultaneous biaxial (SIB) stretching and sequential biaxial (SEB) stretching. The electrical resistivity was first increased up to 1011 Ω cm with the extension of the films, regardless of the stretching modes. Once further stretched to 3.5 × 3.5, the SIB- and SEB-stretched films showed reduction of their resistivity of six and eight orders of magnitude, respectively. Microscopic observations revealed that specimens stretching in SEB mode promoted the elongation of CNTs and their clusters, which was apparently more effective for reconnecting adjacent particles and fabricating a new conducting network.