NASA’s Langley Research Center scientists have developed a process for fabricating carbon nanotube (CNT) structural nanocomposites that brings CNT-based composites closer to realizing their potential for structural applications. Conventional methods fail to properly wet CNTs within the epoxy matrix due to high resin viscosity, resulting in poor infiltration and reduced load transfer between the CNTs and matrix. The NASA process — resistive heating-assisted epoxy infiltration (RHAEI) — uses the CNTs’ electrical resistance to generate heat, which reduces epoxy resin viscosity for greater CNT wetting and adhesion. Mechanical properties are significantly improved compared to conventional methods. NASA’s process has been demonstrated to offer 50% improvement in strength and elastic modulus, with mechanical properties competitive with structural carbon fiber composites.
Carbon nanotubes show promise for a wide range of structural applications due to their outstanding mechanical, electrical, and thermal properties. However, taking advantage of these properties requires fabricating them in composite form, i.e., CNTs embedded in a solid matrix material and comprising at least 50% of the composite. NASA’s invention addresses the need to create strong and stable adhesion between CNTs, and between CNTs and the matrix, through improved infiltration of the CNTs by the epoxy resin.
RHAEI involves application of a low voltage to reduce resin viscosity for improved resin infiltration, followed by a higher voltage for rapid curing. With improved wettability and adhesion of the epoxy on the CNTs, the resulting CNT-reinforced composite offers a 50% improvement in mechanical performance compared to those manufactured with conventional thermal curing. Using CNT tapes for reinforcement, tensile properties of ~700 MPa/g/cc specific strength and ~70 GPa/g/cc specific modulus have been attained.