Ultrahigh strength and modulus of polyimide-carbon nanotube based carbon and graphitic fibers with superior electrical and thermal conductivities for advanced composite applications

Development of carbon fibers (CFs) with high strength and high modulus for structural applications in CF-reinforced polymer (CFRP) industry has been a challenge. Herein, we propose a method for manufacturing highly oriented polymer–carbon nanotube (CNT) composite fibers having high strength (4.8 ± 0.2 GPa), modulus (390 ± 48 GPa), and electrical conductivity (5.75 ± 0.84 MS m-1) by a liquid crystalline wet-spinning process. The use of chlorosulfonic acid (CSA) as a solvent for CNTs and polyimide (PI) promotes dispersion and enables the production of high-performance composite fibers. In addition, the functional groups of PI in composite fibers improve the interfacial shear strength with epoxy resin without sizing additives by 72% compared to that of CNT fibers. Carbonization and graphitization of the composite fibers with an optimal ratio of PI (30%) and CNT cause significant improvement in their mechanical (tensile strength; 6.21 ± 0.3 GPa and modulus; 701 ± 47 GPa) and thermal properties (496 ± 38 W m−1 K−1) by reducing voids and improving orientation. We believe that the polymer–CNT composites and their CFs with high strength and high modulus would be the next-generation CFs for aerospace and defense industry.