Additive manufacturing of conductive and high-strength epoxy-nanoclay-carbon nanotube composites

Additive Manufacturing has increased our ability to fabricate complex shapes and multi-material structures. Epoxy is excellent as the base for structural composite materials. Furthermore, carbon nanotube (CNT) is an outstanding filler due to its unique properties and functionalities. Here, conductive epoxy-nanoclay-CNT nano composite structures were fabricated by direct-write 3D printing. In this process, 3D-printable composite inks were synthesized by incorporation of nanoclay and different concentrations of CNTs - 0.25, 0.5, and 1 vol%, 0.43, 0.86, and 1.7 wt% - in epoxy. CNTs were found to significantly improve the electrical and mechanical properties. Rheological characterization of the inks revealed a shear-thinning behavior for all the nanocomposite inks and an increase in the complex viscosity, storage, and loss moduli with the incorporation of CNTs. The CNT concentration of 0.5 vol% was found to be the optimum condition for enhancement of mechanical properties; an average increase of 61%, 59%, and 31% was measured for flexural strength, flexural modulus, and tensile strength, respectively, compared to the 3D printed epoxy-nanoclay nanocomposite structures. The electrical conductivity of 2.4 x 10(-8) and 2.2 x 10(-6) S/cm was measured for the nanocomposites containing 0.5 and 1 vol % CNTs, respectively. Multi-scale characterization of the morphology revealed partial alignment of CNTs in the direction of printing, CNT pull-out and breakage at the fracture surfaces, and nano-scale interactions of the constituents, all of which contribute to the superiority of the nanocomposite with CNTs. The findings show the promise of this ink material and printing method for various applications such as aerospace structures and electronics.