Evolution of the crystalline structure and cyclization with changing tension during the stabilization of polyacrylonitrile fibers

Abstract

ABSTRACTThe effects of tension on the crystalline structure and cyclization of polyacrylonitrile fibers during stabilization were investigated. The degree of cyclization was measured by Fourier transform infrared spectroscopy and differential scanning calorimetry. The crystalline structure was characterized by wide‐angle X‐ray diffraction. When the fibers were heat‐treated at temperatures between 175 and 218°C, the tension mainly affected the cyclization in the amorphous regions through changes in the spatial distance of the chain segments; this led to a relatively higher cyclization degree under moderate tension. When the temperatures ranged from 226 to 232°C, the reactions extended to the crystalline regions. The chemical bonds became greater in the cross section of the fibers, and this was caused by cyclization structures formed in the former stage. Therefore, the optimum tension was higher than in the prior temperature range. At higher temperatures ranging from 238 to 270°C, a crosslinked structure formed, so the optimum tension increased continually. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42182.