The effect of using two stabilization temperatures and fixation process on preparation of carbon nanofibers

Carbon nanofibers (CNFs) are prepared from electrospun polyacrylonitrile (PAN) because of their high carbon content. Heat treatment (oxidative stabilization and carbonization) is necessary to convert PAN nanofibers into CNFs. The fixation of fibrous structure of polymer precursor during heat treatment is always considered as a problem. The aim of this work is to study the effects of two different stabilization temperatures and fixation on CNFs prepared from electrospun PAN nanofibers. In this study, we use two different stabilization temperatures (275 and 300 °C) to investigate the effect of temperature on the oxidation, cyclization, crosslinking, aromatization, and dehydrogenation processes that occur during the stabilization heat treatment. Further, we study the effect of electrospun sheet fixation during heat treatment on the fibrous structure of electrospun fibers and methods to prevent shrinkage and folding of the electrospun sheet. Fourier transform infrared spectroscopy revealed the effectiveness of stabilization at 300 °C when transforming PAN elctrospun nanofibers to CNFs. Raman spectroscopy showed that carbonization at 800 °C after stabilization at 300 °C lowers the R-value (I_D/I_G ratio) comparing with that stabilized at 275 °C which indicates increasing the amount of structurally ordered graphite crystallites relative to the disordered structure. Scanning electron microscopy (SEM) revealed that fixation process maintained a uniform fibrous structure for the stabilized sheets without shrinkage, whereas carbonization at 800 °C without fixation resulted in deformed and folded carbonized PAN with loss in the fibrous structure.