A Study on Structural Characterization of Thermally Stabilized PAN Precursor Fibers Impregnated with Ammonium Bromide before Carbonization Stage

Abstract

Thermal-oxidative stabilization of polyacrylonitrile (PAN) fiber pretreated with ammonium bromide (NH4Br) was performed in the air atmosphere at temperatures between 200 and 250 degrees C for periods of 5 to 75 min in a multistep approach. The study demonstrates that the NH4Br incorporation is highly effective in accelerating nitrile group cyclization by reducing the time required to form a thermally stable structure. After 60 min of the multistep stabilization, NH4Br incorporated and stabilized PAN was entirely thermally stable, infusible, and non-burning. XRD analysis showed the conversion of the pristine PAN molecular structure from a laterally ordered condition to a very disordered amorphous structure by crosslinking and aromatization process. Infrared analysis indicated rapid and concurrent aromatization and dehydrogenation reactions assisted by the formation of oxygen-containing functional groups. With the progression of the stabilization period, TGA thermograms revealed a comparative increase in thermal stability, as directed by the continuous rise of carbon yield. By decreasing the required time for the stabilization process of PAN fiber, the use of NH4Br impregnation is expected to enhance carbon fiber productivity at a reduced cost considerably.