Study On The Preparation Of Polyacrylonitrile-Based Carbon Nanofibers Through Electrospinning

Many advanced technologies, such as are found in aerospace and renewable energy (e.g. windmill blade structures) have been relying on high performance fibers and their resulting composite materials. But growing concerns regarding energy efficiency and environmental threats are resulting in strong appeals from these industries for a new generation of carbon fibers, exhibiting ultra-light weight and higher performance. Polyacrylonitrile based carbon fibers have been commercialized for several decades. They possess the highest specific strength and specific modulus among all commercially available advanced reinforcing fibers. However, various of structural imperfections, such as nicks, cracks, small holes, pores and sheath/core structure, make high performance carbon fibers hard to prepare. Therefore, to develop a new generation of polyacrylonitrile based carbon fibers with enhanced performance, the fundamental approach has been to reduce the structural imperfections. In this study, polyacrylonitrile based nanofibers are produced by an electrospinning approach and through multi-step hot-stretching, stabilization and carbonization, then converted to carbon nanofibers. Carbon fibers with low imperfections were prepared through combinatorial approach of electrospinning and multi-step hot-stretching techniques. A new way to fabricate continuous high performance carbon fibers in the future was developed.Results of study reveal that a two-step cyclization consisting of intramolecular and intermolecular aspects occurs during stabilization in air. The intermolecular cyclization is initiated by oxygen and is associated with the degree of hot-stretching to the fibers. The resulting carbon nanofibers are highly aligned with quite smooth fiber suface, which has a mean roughness of 0.249 nm. Neither sheath/core structure nor fiber breakage can be found. Most part of resulting carbon nanofibers are turbostratic and the d-spacing of lattice fringe of carbon nanofibers was 0.347 nm. The number of graphic sheets range from 7-15. In the aspects of improving PEI electrical properties, the resulting carbon nanofibers could obviously increase dielectric constant and reduce electrical resistivity of materials and the effects are much better than carbon nanotubes.