Dramatic enhancements in toughness of polyimide nanocomposite via long-CNT-induced long-range creep

Super tough carbon nanotube (CNT) reinforced nanocomposites require both the unique interaction and effective stress transfer between CNTs and polymer chains. When CNT reinforced nanocomposites are stretched, the crack interfaces are usually bridged by CNTs, and energy can be absorbed during deformation before fracture and bring high toughness. However, developing super-tough CNT/polymer nanocomposites which can withstand high matrix deformation yet exploit the superior strength of CNTs is still a great challenge. In this contribution, an ultra-tough CNT/polyimide (PI) nanocomposite was fabricated by a facile in situ polymerization. Super-long vertically aligned CNTs were dispersed into N,N-dimethylacetamide, which is the feedstock for in situ PI polymerization. A long-CNT-induced three-dimensional, continuous, and heterogeneous network is formed to toughen the nanocomposites. By incorporating 0.27 wt% CNTs into a PI matrix, the tensile strength and elongation at break of the nanocomposites reached 156.4 MPa and 140%, respectively, which are 90% and 250% increased compared with the values of pristine PI. Thus, the toughness of the nanocomposites improved 470% and approached 127.4 J g ^-1, well exceeding state-of-the-art tough materials. The reinforcement mechanism reveals that robust tapered fibrils are formed around high-aspect-ratio CNTs to facilitate energy dissipation and enhance the energy absorbing capability. The length of CNTs and the interfacial bonding are important to initiate long-range creep and form robust heterogeneous tapered fibrils to toughen the nanocomposites. The CNT/PI composite film with high toughness, much improved electrical conductivity, as well as high thermal stability, and transparency, broadened their advanced applications in aerospace, aviation, buildings, bulletproof vests, and so on.