Physical Properties of Industrially Produced Carbon Nanotube Yarns for Use in Structural Nanocomposites

Abstract

Industrially-produced carbon nanotube (CNT) networks are a promising base for producing high-performance, continuous CNT nanocomposites, motivating widespread use in research and application development. Floating catalyst chemical vapor deposition (FCCVD) is a highly scalable, widely adopted approach for synthesis of CNT networks; however, FCCVD can yield networks with organic impurities which complicate their characterization and processing. Herein, we analyze two varieties of FCCVD-synthesized commercial (MIRALON®) CNT yarn to explore the effects of densification and purification as they relate to forming infiltrated polymer composites. First, the fluid permeabilities and porosities of neat roving and aggressively chemically-stretched CNT yarns (CSYs) are estimated and compared to gas adsorption studies, which suggest high-tenacity CSYs are largely impermeable, leading to dry-core composites. Next, the presence and effects of oxygen-rich amorphous carbon impurities in the CSYs are identified and found to exist at the scale of CNT bundles, where the amorphous carbon behaves like a hygroscopic polymer matrix in a composite. Removal of the amorphous carbon phase results in a 130%-increase in BET specific surface area and a statistically significant reduction in tensile properties. We discuss challenges in estimating yarn alignment and crystallinity resulting from these factors, and place our results in context of past studies analyzing intrinsic organic coatings in FCCVD-synthesized networks.