Tuning of structural/functional feature of carbon fibers: New insights into the stabilization of polyacrylonitrile

Abstract

The transformation mechanisms from linear polyacrylonitrile (PAN) to ladder structure during stabilization is still controversial. Here, the thermal stabilization mechanism of PAN in nitrogen and air are investigated by variable temperature infrared spectrometry (VTIR), Solid-state (ss) NMR spectroscopy and the density functional theory (DFT). Our results show that the stabilization process of PAN under air is initiated via oxidation reaction, followed by the cyclization and dehydrogenation reaction. Furthermore, during the stabilization of PAN in nitrogen, a new intermediate structure with longer conjugation than the final isolated pyridine ring structure is proposed. Subsequently, we optimized the atmosphere of stabilization process according to the evolution of molecular structure. Consequently, compared with the traditional approach of heat treatment in air, pretreating the precursor fibers in nitrogen at a relative low temperature are shown to improve the char yield by 14.6%, and increase the thermal conductivity by 663%.