(114e) Fundamental Process Parameters and Fiber Formation Mechanisms in Wet-Spinning of Carbon Nanotube Fibers

The mechanical and electrical properties of neat carbon nanotube fiber (CNTF) produced from solutions of pristine CNTs in chlorosulfonic acid are rapidly improving. CNTF is on track to be the strongest synthetic fiber by the end of the decade, and it already surpasses high performance carbon fibers and polymeric fibers in flexibility and electrical/thermal conductivities. As properties begin to exceed those of widely adopted materials (polyaramids, polypropylene, polyethylene, etc.), process cost and environmental efficiency need to be competitive to bring the technology to market. While some research efforts have focused on the impact of the CNT material on CNTF properties, many details of the processing conditions that lead to optimal CNTF properties have not been reported, nor have the mechanisms which limit the formation of CNTF under different conditions. It is understood that CNT solution concentration and spin-line throughput are two primary efficiency determining variables, but the impact of these variables on the spinning window (the range of parameters over which certain grades of CNTF are able to be produced) for the wet spinning process have not yet been thoroughly studied. Here, we seek to define and understand the experimental spinning windows to identify which process parameters govern optimal CNTF properties. We studied the impact of extrusion and take-up parameters, CNT solution concentration, and coagulation conditions on the CNTF properties to determine viable spinning windows. To gain insight and understanding to correlate rheological properties with spinning windows, we measured the viscosity and shear rate behavior of CNT solutions using capillary rheometry. Additionally, we used in-line microscopy on the spinning system to visualize the phenomena occurring at the exit of the spinneret, including die swell, coagulation rate, and mechanisms of filament formation and stability. Finally, we identify the most important factors for CNTF properties and spinning efficiency, and we propose a path forward for efficient production of high-quality CNTF.