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CHAPTER 4 4. CONCLUSIONS This thesis research established fabrication-structure-properties relationships to realize strong carbon nanofibers from PAN precursors and to identify factors that currently limit the ultimately possible tensile properties of this class of nanofibers. Chapter 2 presented the experimental methods and procedures while Chapter 3 discussed the results of this research following the objectives and experimental approaches outlined in Chapter 1. Experiments for PAN nanofibers conducted in the past by this group were used to identify the optimum electrospinning conditions for PAN nanofibers with improved molecular orientation and homogeneous cross-section. With this information as the basis, carbon nanofibers derived from optimized PAN nanofibers were produced with smooth surfaces and uniform diameters along their length. These nanofibers were straight, which is an advantage compared to VGCNFs, which, due to their waviness, do not provide appreciable stiffening to stiff polymer matrices at strains less than 1 - 2%. Individual CNFs with diameters between 150 - 500 nm were tested for their mechanical properties and TEM images of CNFs were obtained to identify the formation of randomly oriented turbostratic carbon crystallites at different carbonization temperatures. It was found that the crystallite size increased with carbonization temperature and was key in tuning the mechanical properties of the CNFs. The tensile strength and the elastic modulus of the CNFs were 6 and 3 times larger than previously reported as a result of selecting appropriate conditions for PAN electrospinning, stabilization and carbonization. The homogenous CNF cross-section 39PDF Image | HIGH STRENGTH CARBON NANOFIBERS DERIVED FROM ELECTROSPUN POLYACRYLONITRILE
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