Characterization of composites with aligned carbon nanotubes (CNTs) as reinforcement

Abstract

Carbon nanotubes' (CNTs) superlative combination of electrical, thermal, and especially mechanical properties make them ideal candidates for composite reinforcement. Nanocomposites and hybrid composite architectures employing traditional advanced composites and CNTs offer significant potential mechanical and multifunctional performance benefits. CNT/polymer composites and two different hybrid architectures are experimentally investigated in this work. A novel process for rapidly growing dense, long, high-quality aligned CNT forests is employed. The first architecture is comprised of aligned fibers with CNTs grown radially on their surface. For the second architecture, dense forests of vertically aligned CNTs are placed between the plies of a laminate, in the through-thickness direction. Fundamental issues related to realizing hybrid composite architectures are investigated experimentally: wetting of the CNTs by commercially available polymers for the different architectures, effective reinforcement of the polymer matrices due to the addition of CNTs, and retention of mechanical (stiffness and strength) properties of the fibers after the CNT growth process.

(cont.) Wetting of CNT forests by several commercial polymers (including a highly-viscous epoxy) is demonstrated at rates conducive to creating a fully-dispersed CNT/matrix region for the two hybrid architectures previously described. Direct measurements of the mechanical properties of nanocomposites are reported for the first time in the literature. Increases in the Young's modulus of the polymer as high as 220% with just 2% volume fraction of aligned CNTs are observed. Equivalent reinforcement had been obtained previously by other authors with 5% volume fraction of randomly oriented CNTs. Single-fiber tension tests indicate no mechanical degradation (stiffness and strength) for alumina fibers undergoing the CNT growth process. Preliminary results on the fabrication of the two hybrid architectures are also presented. All the experimental results presented in this work indicate that hybrid CNT/composite architectures are feasible and future work focuses on mechanical and multifunctional property characterization of these and other hybrid architectures, and scaling to a continuous CNT growth process.