Electrospinning of single wall carbon nanotube reinforced aligned fibrils and yarns

Hoa Le Lam

doi:10.17918/etd-368

Commercial carbon fibers produced from a polyacrylonitrile (PAN) precursor have reached their performance limit. The approach in this study involves the use of single carbon nanotubes (SWNT) with an ultra-high elastic modulus of approximately ~1 TPa and tensile strength of ~ 37 GPa at a breaking strain of ~6 % to reinforce PAN. In order to translate these extraordinary properties to a higher order structure, the need for a media to carry and assemble the SWNT into continuous fibers or yarns is necessary. Effective translation of properties can only be achieved through uniform distribution of SWNT and their alignment in the fiber axis. This has been one of the major challenges since SWNTs tend to agglomerate due to high van der Waals attraction between tubes. It is the goal of this study to develop dispersion technique(s) for the SWNT and process them into aligned fibers utilizing the electrospinning process. The electrospun nanofibers were then characterized by various techniques such as ESEM, Raman microspectroscopy, HRTEM, and tensile testing. Composite nanofibers containing various contents of SWNT up to 10 wt. % with diameter ranging from 40 - 300 nm were successfully electrospun through varying the polymer concentration and spinning parameters. The inclusion of SWNTs and their alignment in the fiber axis were confirmed by Raman microspectroscopy, polarized Raman and HRETEM. The failure mechanism of the nanofibers was investigated by HRTEM through fiber surface fracture. A two stage rupture mechanism was observed where crazing initiates at a surface defect followed by SWNTs pulling out of the PAN matrix. Such mechanisms consume energy therefore strengthening and toughening the fibers. Mechanical drawing of the fiber prior to heat treatment induced molecular orientation resulting in oriented graphite layers in the carbonized fibers. This study has established a processing base and characterization techniques to support the design and development of SWNT reinforced PAN-derived carbon nanofibers. The encouraging results from this study suggest a promising pathway to produce the next generation of high performance CNT reinforced carbon nanofibers. This would help in translating of the remarkable properties of SWNT to macroscopic applications, thus filling the dimensional and properties gap between nanoscopic and macroscopic structures.

Electrospinning of single wall carbon nanotube reinforced aligned fibrils and yarns

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Electrospinning of single wall carbon nanotube reinforced aligned fibrils and yarns

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