Effect of Atmospheres on Stabilization of Polyacrylonitrile Fibers

The effect of atmospheres on stabilization of polyacrylonitrile (PAN) fibers was studied by free shrinkage experiments, Fourier transform infrared spectrometer (FT-IR), elemental analysis, metallographic microscope and tensile testing analysis. FT-IR spectra and elemental analysis of heat treated PAN fibers showed that three main reactions took place, namely cyclization, dehydrogenation and oxidative reactions in oxygen-containing atmospheres. Two main reactions took place, namely cyclization, dehydrogenation reactions in pure nitrogen. The shrinkage indicated that there was crosslinking reaction in oxygen-containing atmospheres. The shrinkage also showed that the chemical shrinkage increased with the increase of oxygen contents in atmospheres. Atmospheres had a sizeable effect on the skin-core structure and tensile strength. When oxygen contents in atmospheres were 20%, 50%, 70% and 100%, the thickness of the outer rings of the skin-core structure increased quickly. The core area continued to decrease and finally almost disappeared. Also, PAN fibers which were stabilized in pure nitrogen did not have skin-core structure. In the oxygen contents which were 20%, 50%, 70% and 100%, the tensile strength decreased quickly. The tensile strength of stabilized PAN fibers in nitrogen was not the lowest.