Mechanical Behavior and Carbon Nanotube/Matrix Interactions of Continuous Carbon Nanotube Yarns for Composite Applications

Carbon nanotubes (CNT) have shown very attractive mechanical properties, compared to current high-performance carbon fiber reinforcements. Recently, continuous CNT yarns (CNTy) have become commercially available and are becoming a promising choice as a reinforcement for composite applications. However, a fiber or yarn is only one piece of a puzzle that must work together in composite materials which is comprised of three key components – reinforcement, matrix, and the interface the reinforcement and matrix share. As such, CNTy materials must be proven to be effective not only as an individual constituent but its relationships with the matrix must be well characterized and understood. In this study, commercially available continuous CNTy and two modified versions with different their morphologies and mechanical performance were characterized. Results indicate that the neat CNTy variants could achieve specific strength of ~ 0.9 N tex-1. When the mechanical results were fit to statistical distributions, 2-parameter Weibull distribution can fit with a nearly 99% goodness-of-it. This indicates that a noticeable brittle failure mechanism to blame the large defects or voids existed in the CNTy materials. With the efforts to improve CNT packing and reduce large voids through high pressure compaction, we observed the specific tensile strength degradation from 0.838 to 0.337 N tex-1 suggesting that degree of alignment was the governing factor for mechanical integrity. Upon addressing the reinforcement properties, the interface was investigated. The commercially available continuous CNTy was modified using heat treatments and acid functionalization. The two treated CNTy and untreated CNTy were analyzed using dynamic contact angle tensiometry and Raman spectroscopy analysis. Two aerospace-grade resin systems were tested alongside to determine their surface tension polar and dispersive components. Together this information provides guidance for how to select CNTy/resin compatibility to maximize composite strength. Lastly, unlike carbon fiber, CNTy do not have a monolithic microstructure, so introducing resin between the CNTy bundles within the yarns aims maximize in-situ interaction subsequently improving mechanical performance. To investigate this effect, CNTy yarn microcomposites were fabricated, and a mechanical study like that of the neat CNTy was conducted. The results show that the combination of SCY/977-3 resin achieve the best mechanical properties over all tested combinations. These results conjointly agree with both the initial neat CNTy mechanical results and the CNTy/resin interface work. Jointly, this work provides a fundamental study of the CNTy materials and reveals great promise that CNTy potentially for reinforcement applications.